Magnetic neutron scattering in Y-type hexagonal ferrite crystals, studied by the author in 1968-1971 and presented in the article showed that the entire density of the so-called magnetic moments of Fe<span style=&q...Magnetic neutron scattering in Y-type hexagonal ferrite crystals, studied by the author in 1968-1971 and presented in the article showed that the entire density of the so-called magnetic moments of Fe<span style="white-space:nowrap;"><sup>3+</sup></span> ions can significantly shift from the position of their nuclei. As result of these shift the structure in form of the chain magnetic spiral is realized in ferrite lattice. The noted shifts of the “magnetic moments” served as the basis for the author’s assumption that these “moments” are “fig sheets” behind which the magnetic poles (magnetic charges) real existing in the shells of atoms are hidden. In this case, the scattering of neutrons is carried out by magnetic charges, and not theoretical surrogates in the form of magnetic moments. In addition to participating in atomic structures, magnetic charges populate potential conduction zones in conductors, where they are exist in compositions of magnetic dipoles. Under the influence of an external magnetic field, a polarization of magnetic dipoles is realized in the conductor, the field strengths of which are directed against the external magnetic field. It is these dipole magnetic fields that are responsible for such a well-known physical phenomenon as diamagnetism. Under the conditions of noted polarization of magnetic dipoles the author managed to perform mechanical separation of magnetic charges in pairs ±g and to charge experienced bodies (metal plates) by the magnetic charges of one sign. The fact of such a charging was detected through magnetostatic interaction between magnetic charges on the plates using highly sensitive torsion balances. This experiment is presented in detail in this article. The results of these experiments, as well as subsequent experimental and theoretical studies of the author, which, in general composition, were carried out from 1968 to the present, showed that magnetic charges are real structural components of the atoms and substance. So, for example, the atomic shells are not electronic but electromagnetic. The main reason that real magnetic charges were <span style="font-family:Verdana;">“</span><span style="font-family:Verdana;">buried alive” in the existing physical theories is the physics of their confinement in substance forces of which, in its rigidity, is many times greater than the electron confinement forces.</span>展开更多
We examine the electronic and magnetic structures of iron telluride KFe2Te2 using first-principle calculations. We demonstrate that the ground state of this compound is in bicollinear antiferromag- netic order with Fe...We examine the electronic and magnetic structures of iron telluride KFe2Te2 using first-principle calculations. We demonstrate that the ground state of this compound is in bicollinear antiferromag- netic order with Fe local moments (- 2.6 μB) that are ferromagnetically aligned along a diagonal direction and antiferromagnetically aligned along the other diagonal in the Fe-Fe square lattice, sim- ilar to the alignment discovered in the parent compound of superconductor α-FeTe. This bicollinear antiferromagnetic order results from the interplay among the nearest, next-nearest, and next-next- nearest neighbor exchange interactions, which are mediated by Te 5p orbitals. This finding may aid our understanding of the interplay between magnetism and superconductivity in the family of iron-based materials.展开更多
The mononuclear radical anionic complex [1-N-methyl-1,10-phenanthrolium][Ni(dmit)2](dmit = 1,3-dithiole-2-thione-4,5-dithiolate) with a new countercation has been prepared and its crystal structure was determined ...The mononuclear radical anionic complex [1-N-methyl-1,10-phenanthrolium][Ni(dmit)2](dmit = 1,3-dithiole-2-thione-4,5-dithiolate) with a new countercation has been prepared and its crystal structure was determined by X-ray crystallography at 298 and 80 K. In the mononuclear radical anionic complex, the nickel ion assumes a slightly distorted square-planar geometry. There are two and three kinds of intermolecular interactions between adjacent mononuclear radical anionic complexes in the crystal at 298 and 80 K, respectively(i.e., Models A and B at 298 K; and Models C, D and E at 80 K). The variable-temperature magnetic moments indicate a strong antiferromagnetic interaction between the adjacent mononuclear radical anionic complexes, and the theoretical calculations reveal that the stronger antiferromagnetic coupling strength at lower temperature should be contributed to the larger overlap integrals between the short contact atoms. This study is the first to reveal the mechanism of stronger magnetic coupling strength at lower temperature for a mononuclear radical anionic nickel complex with dmit as the ligand.展开更多
The crystal structures and magnetic properties of novel Eu TrGa3-r (T=Pd, It, Rh) in termetallic compounds are investigated by using powder x-ray diffraction and magnetic measurements. EuTrGa3-r crystallizes in orth...The crystal structures and magnetic properties of novel Eu TrGa3-r (T=Pd, It, Rh) in termetallic compounds are investigated by using powder x-ray diffraction and magnetic measurements. EuTrGa3-r crystallizes in orthorhombic structure with space group of Cmcm and Z = 4. There are four kinds of nonequivalent 4c crystal positions in EuTrGaa-r unit cell, which are occupied by 4Eu, 4GaⅠ, 4(GaⅡ, T) and 4GaⅢ, respectively. EuTrGa3-r ex- hibits the complex magnetic states in low-temperature regime, with the three-, two- and one-antiferromagnetic transitions occurring for T=Ir, T=Rh and T=Pd, respectively. It might be due to the Kondo effect: a localized antiferromagnetic interaction of the isolated impurity spins with the surrounding conduction electrons at low-temperature regime.展开更多
The reaction of Co^II ions with 1,4-bis(imidazol)butane(bimb) or 1,4-bis(triazol)butane(bitb) in the presence of ClO4^-, respectively affords two CoII coordination complexes, namely {[Co(bimb)3]·2ClO4}n...The reaction of Co^II ions with 1,4-bis(imidazol)butane(bimb) or 1,4-bis(triazol)butane(bitb) in the presence of ClO4^-, respectively affords two CoII coordination complexes, namely {[Co(bimb)3]·2ClO4}n(I) and {[Co(bitb)3]·2ClO4}n(II). Single-crystal X-ray analysis indicates that both complexes I and II show the same α-Po topological structures. However, complex I exhibits a 2-fold interpenetrating network, while complex II features a 3-fold interpenetrating network. In addition, solid-state properties such as thermal stabilities and magnetic properties of two complexes were also investigated.展开更多
The competition between different magnetic structures in hole-doped Fe-pnicitides is explored based on an extended five-orbital Hubbard model including long-range Coulomb interactions.Our results show that the stabili...The competition between different magnetic structures in hole-doped Fe-pnicitides is explored based on an extended five-orbital Hubbard model including long-range Coulomb interactions.Our results show that the stabilized magnetic structure evolves with increasing hole doping level.Namely,the stripe antiferromagnetic phase dominates at zero doping,while magnetic structures with more antiferromagnetic linking numbers such as the staggered tetramer,staggered trimer,and staggered dimer phases become energetically favorable as the hole density increases.At a certain doping level,energy degeneracy of different magnetic structures appears,indicating strong magnetic frustration and magnetic fluctuations in the system.We suggest that the magnetic competition induced by the hole doping may explain the fast decrease of the Neel temperature TNand the moderately suppressed magnetic moment in the hole doped Fe-pnicitides.Moreover,our results show a sign reversal of the kinetic energy anisotropy as the magnetic ground state evolves,which may be the mechanism behind the puzzling sign reversal of the in-plane resistivity anisotropy in hole-doped Fe-pnicitides.展开更多
Large-scale magnetic structures are the main carrier of major eruptions in the solar atmosphere. These structures are rooted in the photosphere and are driven by the unceasing motion of the photospheric material throu...Large-scale magnetic structures are the main carrier of major eruptions in the solar atmosphere. These structures are rooted in the photosphere and are driven by the unceasing motion of the photospheric material through a series of equilibrium configurations. The motion brings energy into the coronal magnetic field until the system ceases to be in equilibrium. The catastrophe theory for solar eruptions indicates that loss of mechanical equilibrium constitutes the main trigger mechanism of major eruptions, usually shown up as solar flares, eruptive prominences, and coronal mass ejections (CMEs). Magnetic reconnection which takes place at the very beginning of the eruption as a result of plasma instabilities/turbulence inside the current sheet, converts magnetic energy into heating and kinetic energy that are responsible for solar flares, and for accelerating both plasma ejecta (flows and CMEs) and energetic particles. Various manifestations are thus related to one another, and the physics behind these relationships is catastrophe and magnetic reconnection. This work reports on recent progress in both theoretical research and observations on eruptive phenomena showing the above manifestations. We start by displaying the properties of large-scale structures in the corona and the related magnetic fields prior to an eruption, and show various morphological features of the disrupting magnetic fields. Then, in the framework of the catastrophe theory, we look into the physics behind those features investigated in a succession of previous works, and discuss the approaches they used.展开更多
Densities and various magnetic parameters (susceptibility, saturation magnetization, saturation isothermal remanent magnetization and intrinsic coercivity) were measured for 20 representative rock samples of different...Densities and various magnetic parameters (susceptibility, saturation magnetization, saturation isothermal remanent magnetization and intrinsic coercivity) were measured for 20 representative rock samples of different lithologies from the Archean Kongling amphibolite to granulite facies terrain of the Yangtze craton. Metasedimentary rocks and tonalitic trondhjemitic granodioritic granitic (TTGG) gneisses show that values of susceptibility κ and saturation isothermal remanent magnetization SIRM are higher than those of amphibolites and gabbros. The felsic gneisses have averages of κ =(1 163±375)×10 -6 SI, SIRM =(18.23±8.38) A/m and R 1=0.083 3± 0.005 7 and the metasedimentary rocks κ =(1 236±823)×10 -6 SI, SIRM =(20.70±10.91) A/m and R I=0.071 4±0.025 2. In contrast, mafic rocks have average κ =(764±316)×10 -6 SI, SIRM = (10.46±3.94)A/m and R 1=0.036±0.009 4, and are dominated by a mixed paramagnetic and ferrimagnetic behavior. Thermal magnetic analyses indicate that magnetite and maghemite of low coercivity are the major carriers of remanent magnetism in the metaclastic sedimentary rocks and TTGG gneisses. The amphibolite and gabbro contain minor amounts of magnetite and pyrrhotite. Magnetism of metaclastic sedimentary rocks and TTGG gneisses is highly heterogeneous; variation coefficients of κ and SIRM are as high as 67 % and 53 % for the former and 32 % and 46 % for the latter. Mineral compositions suggest that biotite may be responsible for the higher magnetism of the metasedimentary rocks. The highest variations in κ, SIRM and R I exhibited by metasedimentary rocks can also be interpreted by their largest absolute variations in biotite mass fraction relative to mafic rocks and felsic gneisses. The average ratio ( Q ) of natural remanent magnetization to induced magnetization of felsic gneisses and metasediments is 0.47 . Ratios ( REM ) of natural remanent to saturation isothermal remanent magnetization ranges between 0.000 001 and 0.027 000 and averages 0.002 540. These values are comparable to those of rocks of similar lithologies from the Archean Taihua high grade terrain of the North China craton and from the Ivrea zone, northern Italy. The dominant phase of magnetism carried by the Kongling rocks is suggested to be thermal remanent magnetization. Consequently, high temperature metamorphism exceeding the Curie point of magnetite (585 ℃) might be responsible for the formation of rock magnetism of the exposed crust in the area of investigation.展开更多
M-T curves, M-H curves and electron spin resonance (ESR) curves of LaMn_(1-x)Zn_xO_3(x=0.05, 0.10, (0.20,) 0.30, 0.40) were studied. Experimental results indicate that: with increasing Zn doping, the T_C value decreas...M-T curves, M-H curves and electron spin resonance (ESR) curves of LaMn_(1-x)Zn_xO_3(x=0.05, 0.10, (0.20,) 0.30, 0.40) were studied. Experimental results indicate that: with increasing Zn doping, the T_C value decreases monotonously, and the system undergoes a transition from long-range ferromagnetic order to cluster-spin glass stated. The results are attributed to double exchange interaction, magnetic dilution and lattice effects by Zn doping.展开更多
The magnetic and structural properties in Co/Cu/Co sandwiches with Ni and Cr buffer layers were investigated. It was found that the coercivity in Ni layer buffered samples decreases with increasing Ni layer thickness,...The magnetic and structural properties in Co/Cu/Co sandwiches with Ni and Cr buffer layers were investigated. It was found that the coercivity in Ni layer buffered samples decreases with increasing Ni layer thickness, while that in Cr layer buffered ones increases with increasing Cr layer thickness, leading to a large difference in field sensitivity of their giant magnetoresistance (GMR) properties. X-ray diffraction and high resolution transmission electron microscope images exhibited that there is a strong fcc (111) texture in the samples with Ni buffer layer. But there are only randomly oriented potycrystalline grains in Cr buffered sandwiches. According to atomic force microscope topography, the surface roughness of Cr buffered sandwiches is smaller than that of Ni buffered ones. It is demonstrated that buffer layer influences both magnetic and structural properties in Co/Cu/Co sandwiches as well as their GMR characteristics.展开更多
In this paper, we review the magnetic properties and magnetocaloric effects(MCE) of binary R–T(R = Pr, Gd, Tb,Dy, Ho, Er, Tm; T = Ga, Ni, Co, Cu) intermetallic compounds(including RGa series, RNi series, R_(12...In this paper, we review the magnetic properties and magnetocaloric effects(MCE) of binary R–T(R = Pr, Gd, Tb,Dy, Ho, Er, Tm; T = Ga, Ni, Co, Cu) intermetallic compounds(including RGa series, RNi series, R_(12)Co_7 series, R_3 Co series and RCu_2series), which have been investigated in detail in the past several years. The R–T compounds are studied by means of magnetic measurements, heat capacity measurements, magnetoresistance measurements and neutron powder diffraction measurements. The R–T compounds show complex magnetic transitions and interesting magnetic properties.The types of magnetic transitions are investigated and confirmed in detail by multiple approaches. Especially, most of the R–T compounds undergo more than one magnetic transition, which has significant impact on the magnetocaloric effect of R–T compounds. The MCE of R–T compounds are calculated by different ways and the special shapes of MCE peaks for different compounds are investigated and discussed in detail. To improve the MCE performance of R–T compounds,atoms with large spin(S) and atoms with large total angular momentum(J) are introduced to substitute the related rare earth atoms. With the atom substitution, the maximum of magnetic entropy change(?SM), refrigerant temperature width(Twidth)or refrigerant capacity(RC) is enlarged for some R–T compounds. In the low temperature range, binary R–T(R = Pr, Gd,Tb, Dy, Ho, Er, Tm; T = Ga, Ni, Co, Cu) intermetallic compounds(including RGa series, RNi series,R_(12)Co_7 series, R_3 Co series and RCu_2series) show excellent performance of MCE, indicating the potential application for gas liquefaction in the future.展开更多
BACKGROUND The main clinical manifestation of Alzheimer’s disease(AD)is memory loss,which can be accompanied by neuropsychiatric symptoms at different stages of the disease.Amygdala is closely related to emotion and ...BACKGROUND The main clinical manifestation of Alzheimer’s disease(AD)is memory loss,which can be accompanied by neuropsychiatric symptoms at different stages of the disease.Amygdala is closely related to emotion and memory.AIM To evaluate the diagnostic value of amygdala on structural magnetic resonance imaging(sMRI)for AD.METHODS In this study,22 patients with AD and 26 controls were enrolled.Their amygdala volumes were measured by sMRI and analyzed using an automatic analysis software.RESULTS The bilateral amygdala volumes of AD patients were significantly lower than those of the controls and were positively correlated with the hippocampal volumes.Receiver operating characteristic curve analyses showed that the sensitivity of the left and right amygdala volumes in diagnosing AD was 80.8%and 88.5%,respectively.Subgroup analyses showed that amygdala atrophy was more serious in AD patients with neuropsychiatric symptoms,which mainly included irritability(22.73%),sleep difficulties(22.73%),apathy(18.18%),and hallucination(13.64%).CONCLUSION Amygdala volumes measured by sMRI can be used to diagnose AD,and amygdala atrophy is more serious in patients with neuropsychiatric symptoms.展开更多
Ferromagnetic shape memory Ni-Mn-Ga films with 7M modulated structure were prepared on MgO (001) substrates by magnetron sputtering. Magnetization process with a typical two-hysteresis loop indicates the occurrence ...Ferromagnetic shape memory Ni-Mn-Ga films with 7M modulated structure were prepared on MgO (001) substrates by magnetron sputtering. Magnetization process with a typical two-hysteresis loop indicates the occurrence of the reversible magnetic field-induced reorientation. Magnetic domain structure and twin structure of the film were controlled by the in- terplay of the magnetic and temperature field. With cooling under an out-of-plane magnetic field, the evolution of magnetic domain structure reveals that martensitic transformation could be divided into two periods: nucleation and growth. With an in-plane magnetic field applied to a thermomagnetic-treated film, the evolution of magnetic domain structure gives evidence of a reorientation of twin variants of martensite. A microstructural model is described to define the twin structure and to produce the magnetic domain structure at the beginning of martensitic transformation; based on this model, the relationship between the twin structure and the magnetic domain structure for the treated film under an in-plane field is also described.展开更多
Based on the CHAMP Magsat data set, spherical cap harmonic analysis was used to model the magnetic fields over China continent. The data set used in the analysis includes the 15′×15′ gridded values of the CHAMP...Based on the CHAMP Magsat data set, spherical cap harmonic analysis was used to model the magnetic fields over China continent. The data set used in the analysis includes the 15′×15′ gridded values of the CHAMP anomaly fields (latitude φ=25°N to 50°N and longitude λ=78°E to 135°E). The pole of the cap is located at φ=35°N and λ=110°E with half-angle of 30°. The maximum index (K max) of the model is 30 and the total number of model coefficients is 961, which corresponds to the minimum wavelength at the earth's surface about 400 km. The root mean square (RMS) deviations between the calculated and observed values are ~ 4 nT for ΔX, ~ 3 nT for ΔY and ~ 3.5 nT for ΔZ, respectively. Results show that positive anomalies are found mainly at the Tarim basin with ~6- 8 nT, the Yangtze platform and North China platform with ~4 nT, and the Songliao basin with ~4-6 nT. In contrast, negative anomaly is mainly located in the Tibet orogenic belt with the amplitude ~ (-6)-(-8) nT. Upward continuation of magnetic anomalies was used to semi-quantitatively separate the magnetic anomalies in different depths of crust. The magnetic anomalies at the earth's surface are from -6 to 10 nT for upper crust, middle crust -27 to 42 nT and lower crust -12 to 18 nT, respectively. The strikes of the magnetic anomalies for the upper crust are consistent with those for the middle crust, but not for the lower crust. The high positive magnetic anomalies mainly result from the old continental nucleus and diastrophic block (e.g. middle Sichuan continental nucleus, middle Tarim basin continental nucleus, Junggar diastrophic block and Qaidam diastrophic block). The amplitudes of the magnetic anomalies of the old continental nucleus and diastrophic block are related to evolution of deep crust. These results improve our understanding of the crustal structure over China continent.展开更多
A dinuclear Tb(Ⅲ) compound, Tb_2(μ_2-anthc)_4(anthc)_2(1,10-phen)_2(1, Hanthc = 9-anthracenecarboxylic acid and 1,10-phen = 1,10-phenanthroline), was synthesized under solvothermal condition and structural...A dinuclear Tb(Ⅲ) compound, Tb_2(μ_2-anthc)_4(anthc)_2(1,10-phen)_2(1, Hanthc = 9-anthracenecarboxylic acid and 1,10-phen = 1,10-phenanthroline), was synthesized under solvothermal condition and structurally characterized by single-crystal X-ray diffraction. Compound 1 crystallizes in the triclinic system, space group P1, with a = 12.5061(12), b = 13.3168(10), c = 15.0079(12) ?, α = 110.620(7), β = 102.941(7), γ = 107.036(7)o, V = 2081.8(3) ?~3, Z = 1, C_(114)H_(70)N_4O_(12)Tb_2, M_r = 2005.58, D_c = 1.600 g/cm^3, μ = 1.759 mm^(-1), F(000) = 1008, the final R = 0.0294 and w R = 0.0608 for 8900 observed reflections with I 〉 2s(I). In compound 1, two Tb(Ⅲ) ions are linked by four carboxylate groups of the bridging anthc– ligands to give a dinuclear Tb_2(μ_2-anthc)_4 unit wherein each Tb(III) ion is further capped by a terminal anthc– ligand and a 1,10-phen ligand in a chelating fashion. Detailed direct-current and alternating-current susceptibility measurements showed no slow magnetism relaxation phenomenon was observed for 1.展开更多
The structure, magnetization, and magnetocrystalline anisotropy wereinvestigated using X-ray diffraction, vibrating sample magnetometer, and AC susceptibility-meter Itis found that the microstructure of (Sm_(0.5)Nd_(0...The structure, magnetization, and magnetocrystalline anisotropy wereinvestigated using X-ray diffraction, vibrating sample magnetometer, and AC susceptibility-meter Itis found that the microstructure of (Sm_(0.5)Nd_(0.5))_2(Fe_(1-x)Co_x)_(17) alloys is an(Sm,Nd)_2(Fe,Co)_(17) phase with the rhombohedral Th_2Zn_(17)-type structure. The Curie temperatureT_c increases with the Co concentration increasing, and the magnetization first increases as the Cocontent increases in (Sm_(0.5)Nd_(0.5))_2(Fe_(1-x)Co_x)_(17) alloys and then decreases slowly. Theeasy magnetization direction (EMD) of (Sm_(0.5)Nd_(0.5))_2(Fe_(0.25)Co_(0.75))_(17) is along thec-axis and a strong enhancement of the crystalline anisotropy energy constant K is produced by theaddition of some Co atoms. The anisotropy energy constant reaches the maximum when x = 0.75 and thendecreases slowly with the Co content further increasing. The(Sm_(0.5)Nd_(0.5))_2(Fe_(0.25)Co_(0.75))_(17) compound is an optical candidate for the new permanentmagnet, which possesses a high magnetization, a high Curie temperature, and a large anisotropy.展开更多
A new ternary neodymium zirconium sulfide Nd_2ZrS_5 was synthesized by high-temperature solid-state reaction and structurally characterized by single-crystal X-ray diffraction. It crystallizes in the orthorhombic spac...A new ternary neodymium zirconium sulfide Nd_2ZrS_5 was synthesized by high-temperature solid-state reaction and structurally characterized by single-crystal X-ray diffraction. It crystallizes in the orthorhombic space group Pnma(No. 62) belonging to the Y_2HfS_5 structure-type with a = 11.461(4), b = 8.009(3), c = 7.315(3) A, Z = 2 and V = 671.5(4)A3. Its structure features NdS_8 and ZrS_7 polyhedra-constructed a 3-D network. The data of magnetic susceptibility indicate its antiferromagnetic-like behavior without magnetic order down to 2 K.展开更多
Two new coordination polymers,namely,{[Cd(1.5)(bc)2(HL)](13)H2O}(2n)(1) and [Mn(ip)(H2L)(H2O)]n(2)(H2L = 3-(1 H-pyrazol-4-yl)-5-(pyridin-2-yl)-1,2,4-triazole,Hbc = benzoic acid,H2 ip = isophth...Two new coordination polymers,namely,{[Cd(1.5)(bc)2(HL)](13)H2O}(2n)(1) and [Mn(ip)(H2L)(H2O)]n(2)(H2L = 3-(1 H-pyrazol-4-yl)-5-(pyridin-2-yl)-1,2,4-triazole,Hbc = benzoic acid,H2 ip = isophthalic acid) were constructed by solvothermal reaction.The compounds were characterized by elemental analysis,FT-IR spectroscopy,and single-crystal X-ray diffraction.Compound 1 displays a two-dimensional plane structure consisting of [Cd3(bc)2(HL)] subunits.Compound 2 possesses a one-dimensional chain structure and is further extended into a 3-D supramolecular architecture via hydrogen bonds.Moreover,photoluminescence studies showed compound 1 exhibits luminescent emissions with emission maxima at 375 nm.Magnetic susceptibility measurements of 2 indicate that domain antiferromagnetic interactions exist between Mn(Ⅱ) ions.In addition,thermogravimetric properties of 1 and 2 were also measured.展开更多
The alloy with nominal composition Sm_2(Fe0.94Ti0.06)17 is prepared by arc-melting, hydrogenation and nitrogenation processes. The Sm_2(Fe0.94Ti0.06)17 alloy has a single phase of Sm_3(Fe, Ti)29 with the Nd_3(Fe, Ti)...The alloy with nominal composition Sm_2(Fe0.94Ti0.06)17 is prepared by arc-melting, hydrogenation and nitrogenation processes. The Sm_2(Fe0.94Ti0.06)17 alloy has a single phase of Sm_3(Fe, Ti)29 with the Nd_3(Fe, Ti)29-type structure. The corresponding hydride phase with the same phase structure of the parent alloy was formed after a hydrogen decrepitation (HD) process at 300℃. The hydrogenation at 800℃ mainly shows a HDDR process. The HD and nitrogenation at 500℃ result in increasing the Curie temperature of the alloy by 72℃ and by 158℃ due to lattice expansions, respectively. The anisotropic and isotropic Sm_3(Fe. Ti)29N_y magnets are obtained after HD, HDDR and the consequent nitrogenation, respectively. The optimum magnetic properties of Sm_3(Fe, Ti)29N_y powders achieved in the above two processes are: (i) B_r=0;82 T, _iH_c=4.48 kA/cm. (BH)_max=54.3 kJ/m^3, (ii) B_r=0.68 T, _iH_c=8.14 kA/cm, (BH)max=66.4 kJ/m^3.展开更多
The crystal structure,magnetization,and spontaneous magnetostriction of ferromagnetic Laves phase Gd Fe2 compound have been investigated.High resolution synchrotron x-ray diffraction(XRD) analysis shows that Gd Fe2 ...The crystal structure,magnetization,and spontaneous magnetostriction of ferromagnetic Laves phase Gd Fe2 compound have been investigated.High resolution synchrotron x-ray diffraction(XRD) analysis shows that Gd Fe2 has a lower cubic symmetry with easy magnetization direction(EMD) along [100] below Curie temperature TC.The replacement of Gd with a small amount of Tb changes the EMD to [111].The Curie temperature decreases while the field dependence of the saturation magnetization(Ms) measured in temperature range 5–300 K varies with increasing Tb concentration.Coercivity Hc increases with increasing Tb concentration and decays exponentially as temperature increases.The anisotropy in Gd Fe2 is so weak that some of the rare-earth substitution plays an important role in determining the easy direction of magnetization in GdFe_2.The calculated magnetostrictive constant λ100 shows a small value of 37×10^(-6).This value agrees well with experimental data 30×10^(-6).Under a relatively small magnetic field,GdFe_2 exhibits a V-shaped positive magnetostriction curve.When the field is further increased,the crystal exhibits a negative magnetostriction curve.This phenomenon has been discussed in term of magnetic domain switching.Furthermore,magnetostriction increases with increasing Tb concentration.Our work leads to a simple and unified mesoscopic explanation for magnetostriction in ferromagnets.It may also provide insight for developing novel functional materials.展开更多
文摘Magnetic neutron scattering in Y-type hexagonal ferrite crystals, studied by the author in 1968-1971 and presented in the article showed that the entire density of the so-called magnetic moments of Fe<span style="white-space:nowrap;"><sup>3+</sup></span> ions can significantly shift from the position of their nuclei. As result of these shift the structure in form of the chain magnetic spiral is realized in ferrite lattice. The noted shifts of the “magnetic moments” served as the basis for the author’s assumption that these “moments” are “fig sheets” behind which the magnetic poles (magnetic charges) real existing in the shells of atoms are hidden. In this case, the scattering of neutrons is carried out by magnetic charges, and not theoretical surrogates in the form of magnetic moments. In addition to participating in atomic structures, magnetic charges populate potential conduction zones in conductors, where they are exist in compositions of magnetic dipoles. Under the influence of an external magnetic field, a polarization of magnetic dipoles is realized in the conductor, the field strengths of which are directed against the external magnetic field. It is these dipole magnetic fields that are responsible for such a well-known physical phenomenon as diamagnetism. Under the conditions of noted polarization of magnetic dipoles the author managed to perform mechanical separation of magnetic charges in pairs ±g and to charge experienced bodies (metal plates) by the magnetic charges of one sign. The fact of such a charging was detected through magnetostatic interaction between magnetic charges on the plates using highly sensitive torsion balances. This experiment is presented in detail in this article. The results of these experiments, as well as subsequent experimental and theoretical studies of the author, which, in general composition, were carried out from 1968 to the present, showed that magnetic charges are real structural components of the atoms and substance. So, for example, the atomic shells are not electronic but electromagnetic. The main reason that real magnetic charges were <span style="font-family:Verdana;">“</span><span style="font-family:Verdana;">buried alive” in the existing physical theories is the physics of their confinement in substance forces of which, in its rigidity, is many times greater than the electron confinement forces.</span>
文摘We examine the electronic and magnetic structures of iron telluride KFe2Te2 using first-principle calculations. We demonstrate that the ground state of this compound is in bicollinear antiferromag- netic order with Fe local moments (- 2.6 μB) that are ferromagnetically aligned along a diagonal direction and antiferromagnetically aligned along the other diagonal in the Fe-Fe square lattice, sim- ilar to the alignment discovered in the parent compound of superconductor α-FeTe. This bicollinear antiferromagnetic order results from the interplay among the nearest, next-nearest, and next-next- nearest neighbor exchange interactions, which are mediated by Te 5p orbitals. This finding may aid our understanding of the interplay between magnetism and superconductivity in the family of iron-based materials.
基金supported by the National Natural Science Foundation of China(No.20971080)the Natural Science Foundation of Shandong Province(No.ZR2013BM009)
文摘The mononuclear radical anionic complex [1-N-methyl-1,10-phenanthrolium][Ni(dmit)2](dmit = 1,3-dithiole-2-thione-4,5-dithiolate) with a new countercation has been prepared and its crystal structure was determined by X-ray crystallography at 298 and 80 K. In the mononuclear radical anionic complex, the nickel ion assumes a slightly distorted square-planar geometry. There are two and three kinds of intermolecular interactions between adjacent mononuclear radical anionic complexes in the crystal at 298 and 80 K, respectively(i.e., Models A and B at 298 K; and Models C, D and E at 80 K). The variable-temperature magnetic moments indicate a strong antiferromagnetic interaction between the adjacent mononuclear radical anionic complexes, and the theoretical calculations reveal that the stronger antiferromagnetic coupling strength at lower temperature should be contributed to the larger overlap integrals between the short contact atoms. This study is the first to reveal the mechanism of stronger magnetic coupling strength at lower temperature for a mononuclear radical anionic nickel complex with dmit as the ligand.
基金Supported by the National Natural Science Foundation of China under Grant No 11274110
文摘The crystal structures and magnetic properties of novel Eu TrGa3-r (T=Pd, It, Rh) in termetallic compounds are investigated by using powder x-ray diffraction and magnetic measurements. EuTrGa3-r crystallizes in orthorhombic structure with space group of Cmcm and Z = 4. There are four kinds of nonequivalent 4c crystal positions in EuTrGaa-r unit cell, which are occupied by 4Eu, 4GaⅠ, 4(GaⅡ, T) and 4GaⅢ, respectively. EuTrGa3-r ex- hibits the complex magnetic states in low-temperature regime, with the three-, two- and one-antiferromagnetic transitions occurring for T=Ir, T=Rh and T=Pd, respectively. It might be due to the Kondo effect: a localized antiferromagnetic interaction of the isolated impurity spins with the surrounding conduction electrons at low-temperature regime.
基金Supported by the National Natural Science Foundation of China(Nos.21301106,21201109 and 21373122)
文摘The reaction of Co^II ions with 1,4-bis(imidazol)butane(bimb) or 1,4-bis(triazol)butane(bitb) in the presence of ClO4^-, respectively affords two CoII coordination complexes, namely {[Co(bimb)3]·2ClO4}n(I) and {[Co(bitb)3]·2ClO4}n(II). Single-crystal X-ray analysis indicates that both complexes I and II show the same α-Po topological structures. However, complex I exhibits a 2-fold interpenetrating network, while complex II features a 3-fold interpenetrating network. In addition, solid-state properties such as thermal stabilities and magnetic properties of two complexes were also investigated.
基金the Guangxi Natural Science Foundation,China(Grant Nos.2022GXNSFAA035560and GuikeAD20159009)the Scientific Research Foundation of Guilin University of Technology(Grant No.GLUTQD2017009)。
文摘The competition between different magnetic structures in hole-doped Fe-pnicitides is explored based on an extended five-orbital Hubbard model including long-range Coulomb interactions.Our results show that the stabilized magnetic structure evolves with increasing hole doping level.Namely,the stripe antiferromagnetic phase dominates at zero doping,while magnetic structures with more antiferromagnetic linking numbers such as the staggered tetramer,staggered trimer,and staggered dimer phases become energetically favorable as the hole density increases.At a certain doping level,energy degeneracy of different magnetic structures appears,indicating strong magnetic frustration and magnetic fluctuations in the system.We suggest that the magnetic competition induced by the hole doping may explain the fast decrease of the Neel temperature TNand the moderately suppressed magnetic moment in the hole doped Fe-pnicitides.Moreover,our results show a sign reversal of the kinetic energy anisotropy as the magnetic ground state evolves,which may be the mechanism behind the puzzling sign reversal of the in-plane resistivity anisotropy in hole-doped Fe-pnicitides.
基金the National Natural Science Foundation of China.
文摘Large-scale magnetic structures are the main carrier of major eruptions in the solar atmosphere. These structures are rooted in the photosphere and are driven by the unceasing motion of the photospheric material through a series of equilibrium configurations. The motion brings energy into the coronal magnetic field until the system ceases to be in equilibrium. The catastrophe theory for solar eruptions indicates that loss of mechanical equilibrium constitutes the main trigger mechanism of major eruptions, usually shown up as solar flares, eruptive prominences, and coronal mass ejections (CMEs). Magnetic reconnection which takes place at the very beginning of the eruption as a result of plasma instabilities/turbulence inside the current sheet, converts magnetic energy into heating and kinetic energy that are responsible for solar flares, and for accelerating both plasma ejecta (flows and CMEs) and energetic particles. Various manifestations are thus related to one another, and the physics behind these relationships is catastrophe and magnetic reconnection. This work reports on recent progress in both theoretical research and observations on eruptive phenomena showing the above manifestations. We start by displaying the properties of large-scale structures in the corona and the related magnetic fields prior to an eruption, and show various morphological features of the disrupting magnetic fields. Then, in the framework of the catastrophe theory, we look into the physics behind those features investigated in a succession of previous works, and discuss the approaches they used.
文摘Densities and various magnetic parameters (susceptibility, saturation magnetization, saturation isothermal remanent magnetization and intrinsic coercivity) were measured for 20 representative rock samples of different lithologies from the Archean Kongling amphibolite to granulite facies terrain of the Yangtze craton. Metasedimentary rocks and tonalitic trondhjemitic granodioritic granitic (TTGG) gneisses show that values of susceptibility κ and saturation isothermal remanent magnetization SIRM are higher than those of amphibolites and gabbros. The felsic gneisses have averages of κ =(1 163±375)×10 -6 SI, SIRM =(18.23±8.38) A/m and R 1=0.083 3± 0.005 7 and the metasedimentary rocks κ =(1 236±823)×10 -6 SI, SIRM =(20.70±10.91) A/m and R I=0.071 4±0.025 2. In contrast, mafic rocks have average κ =(764±316)×10 -6 SI, SIRM = (10.46±3.94)A/m and R 1=0.036±0.009 4, and are dominated by a mixed paramagnetic and ferrimagnetic behavior. Thermal magnetic analyses indicate that magnetite and maghemite of low coercivity are the major carriers of remanent magnetism in the metaclastic sedimentary rocks and TTGG gneisses. The amphibolite and gabbro contain minor amounts of magnetite and pyrrhotite. Magnetism of metaclastic sedimentary rocks and TTGG gneisses is highly heterogeneous; variation coefficients of κ and SIRM are as high as 67 % and 53 % for the former and 32 % and 46 % for the latter. Mineral compositions suggest that biotite may be responsible for the higher magnetism of the metasedimentary rocks. The highest variations in κ, SIRM and R I exhibited by metasedimentary rocks can also be interpreted by their largest absolute variations in biotite mass fraction relative to mafic rocks and felsic gneisses. The average ratio ( Q ) of natural remanent magnetization to induced magnetization of felsic gneisses and metasediments is 0.47 . Ratios ( REM ) of natural remanent to saturation isothermal remanent magnetization ranges between 0.000 001 and 0.027 000 and averages 0.002 540. These values are comparable to those of rocks of similar lithologies from the Archean Taihua high grade terrain of the North China craton and from the Ivrea zone, northern Italy. The dominant phase of magnetism carried by the Kongling rocks is suggested to be thermal remanent magnetization. Consequently, high temperature metamorphism exceeding the Curie point of magnetite (585 ℃) might be responsible for the formation of rock magnetism of the exposed crust in the area of investigation.
文摘M-T curves, M-H curves and electron spin resonance (ESR) curves of LaMn_(1-x)Zn_xO_3(x=0.05, 0.10, (0.20,) 0.30, 0.40) were studied. Experimental results indicate that: with increasing Zn doping, the T_C value decreases monotonously, and the system undergoes a transition from long-range ferromagnetic order to cluster-spin glass stated. The results are attributed to double exchange interaction, magnetic dilution and lattice effects by Zn doping.
文摘The magnetic and structural properties in Co/Cu/Co sandwiches with Ni and Cr buffer layers were investigated. It was found that the coercivity in Ni layer buffered samples decreases with increasing Ni layer thickness, while that in Cr layer buffered ones increases with increasing Cr layer thickness, leading to a large difference in field sensitivity of their giant magnetoresistance (GMR) properties. X-ray diffraction and high resolution transmission electron microscope images exhibited that there is a strong fcc (111) texture in the samples with Ni buffer layer. But there are only randomly oriented potycrystalline grains in Cr buffered sandwiches. According to atomic force microscope topography, the surface roughness of Cr buffered sandwiches is smaller than that of Ni buffered ones. It is demonstrated that buffer layer influences both magnetic and structural properties in Co/Cu/Co sandwiches as well as their GMR characteristics.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11274357,51501005,51590880,and 11674008)the Fundamental Research Funds for the Central Universities,China(Grant No.FRF-TP-15-010A1)+1 种基金the China Postdoctoral Science Foundation(Grant No.2016M591071)the Key Research Program of the Chinese Academy of Sciences(Grant No.KJZD-EW-M05)
文摘In this paper, we review the magnetic properties and magnetocaloric effects(MCE) of binary R–T(R = Pr, Gd, Tb,Dy, Ho, Er, Tm; T = Ga, Ni, Co, Cu) intermetallic compounds(including RGa series, RNi series, R_(12)Co_7 series, R_3 Co series and RCu_2series), which have been investigated in detail in the past several years. The R–T compounds are studied by means of magnetic measurements, heat capacity measurements, magnetoresistance measurements and neutron powder diffraction measurements. The R–T compounds show complex magnetic transitions and interesting magnetic properties.The types of magnetic transitions are investigated and confirmed in detail by multiple approaches. Especially, most of the R–T compounds undergo more than one magnetic transition, which has significant impact on the magnetocaloric effect of R–T compounds. The MCE of R–T compounds are calculated by different ways and the special shapes of MCE peaks for different compounds are investigated and discussed in detail. To improve the MCE performance of R–T compounds,atoms with large spin(S) and atoms with large total angular momentum(J) are introduced to substitute the related rare earth atoms. With the atom substitution, the maximum of magnetic entropy change(?SM), refrigerant temperature width(Twidth)or refrigerant capacity(RC) is enlarged for some R–T compounds. In the low temperature range, binary R–T(R = Pr, Gd,Tb, Dy, Ho, Er, Tm; T = Ga, Ni, Co, Cu) intermetallic compounds(including RGa series, RNi series,R_(12)Co_7 series, R_3 Co series and RCu_2series) show excellent performance of MCE, indicating the potential application for gas liquefaction in the future.
基金Supported by The Young Talents Fund of the Second Hospital of Shandong University,No.2018YT16Rongxiang Regenerative Medicine Foundation of Shandong University,No.2019SDRX-09.
文摘BACKGROUND The main clinical manifestation of Alzheimer’s disease(AD)is memory loss,which can be accompanied by neuropsychiatric symptoms at different stages of the disease.Amygdala is closely related to emotion and memory.AIM To evaluate the diagnostic value of amygdala on structural magnetic resonance imaging(sMRI)for AD.METHODS In this study,22 patients with AD and 26 controls were enrolled.Their amygdala volumes were measured by sMRI and analyzed using an automatic analysis software.RESULTS The bilateral amygdala volumes of AD patients were significantly lower than those of the controls and were positively correlated with the hippocampal volumes.Receiver operating characteristic curve analyses showed that the sensitivity of the left and right amygdala volumes in diagnosing AD was 80.8%and 88.5%,respectively.Subgroup analyses showed that amygdala atrophy was more serious in AD patients with neuropsychiatric symptoms,which mainly included irritability(22.73%),sleep difficulties(22.73%),apathy(18.18%),and hallucination(13.64%).CONCLUSION Amygdala volumes measured by sMRI can be used to diagnose AD,and amygdala atrophy is more serious in patients with neuropsychiatric symptoms.
基金supported by the National Key Project of Fundamental Research of China(Grant No.2012CB932304)the National Natural Science Foundation of China(Grant No.50831006)+1 种基金the Program for New Century Excellent Talents in University(Grant No.NCET-11-0156)the Priority Academic Program Development of Jiangsu Higher Education Institutions
文摘Ferromagnetic shape memory Ni-Mn-Ga films with 7M modulated structure were prepared on MgO (001) substrates by magnetron sputtering. Magnetization process with a typical two-hysteresis loop indicates the occurrence of the reversible magnetic field-induced reorientation. Magnetic domain structure and twin structure of the film were controlled by the in- terplay of the magnetic and temperature field. With cooling under an out-of-plane magnetic field, the evolution of magnetic domain structure reveals that martensitic transformation could be divided into two periods: nucleation and growth. With an in-plane magnetic field applied to a thermomagnetic-treated film, the evolution of magnetic domain structure gives evidence of a reorientation of twin variants of martensite. A microstructural model is described to define the twin structure and to produce the magnetic domain structure at the beginning of martensitic transformation; based on this model, the relationship between the twin structure and the magnetic domain structure for the treated film under an in-plane field is also described.
基金ThispaperissupportedbytheChinese" 973"Program (No .2 0 0 3CD71 650 6)
文摘Based on the CHAMP Magsat data set, spherical cap harmonic analysis was used to model the magnetic fields over China continent. The data set used in the analysis includes the 15′×15′ gridded values of the CHAMP anomaly fields (latitude φ=25°N to 50°N and longitude λ=78°E to 135°E). The pole of the cap is located at φ=35°N and λ=110°E with half-angle of 30°. The maximum index (K max) of the model is 30 and the total number of model coefficients is 961, which corresponds to the minimum wavelength at the earth's surface about 400 km. The root mean square (RMS) deviations between the calculated and observed values are ~ 4 nT for ΔX, ~ 3 nT for ΔY and ~ 3.5 nT for ΔZ, respectively. Results show that positive anomalies are found mainly at the Tarim basin with ~6- 8 nT, the Yangtze platform and North China platform with ~4 nT, and the Songliao basin with ~4-6 nT. In contrast, negative anomaly is mainly located in the Tibet orogenic belt with the amplitude ~ (-6)-(-8) nT. Upward continuation of magnetic anomalies was used to semi-quantitatively separate the magnetic anomalies in different depths of crust. The magnetic anomalies at the earth's surface are from -6 to 10 nT for upper crust, middle crust -27 to 42 nT and lower crust -12 to 18 nT, respectively. The strikes of the magnetic anomalies for the upper crust are consistent with those for the middle crust, but not for the lower crust. The high positive magnetic anomalies mainly result from the old continental nucleus and diastrophic block (e.g. middle Sichuan continental nucleus, middle Tarim basin continental nucleus, Junggar diastrophic block and Qaidam diastrophic block). The amplitudes of the magnetic anomalies of the old continental nucleus and diastrophic block are related to evolution of deep crust. These results improve our understanding of the crustal structure over China continent.
基金Supported by the National Natural Science Foundation of China(No.21361011 and 21101081)Science Founds of State Key Laboratory of Structural Chemistry(20130011)
文摘A dinuclear Tb(Ⅲ) compound, Tb_2(μ_2-anthc)_4(anthc)_2(1,10-phen)_2(1, Hanthc = 9-anthracenecarboxylic acid and 1,10-phen = 1,10-phenanthroline), was synthesized under solvothermal condition and structurally characterized by single-crystal X-ray diffraction. Compound 1 crystallizes in the triclinic system, space group P1, with a = 12.5061(12), b = 13.3168(10), c = 15.0079(12) ?, α = 110.620(7), β = 102.941(7), γ = 107.036(7)o, V = 2081.8(3) ?~3, Z = 1, C_(114)H_(70)N_4O_(12)Tb_2, M_r = 2005.58, D_c = 1.600 g/cm^3, μ = 1.759 mm^(-1), F(000) = 1008, the final R = 0.0294 and w R = 0.0608 for 8900 observed reflections with I 〉 2s(I). In compound 1, two Tb(Ⅲ) ions are linked by four carboxylate groups of the bridging anthc– ligands to give a dinuclear Tb_2(μ_2-anthc)_4 unit wherein each Tb(III) ion is further capped by a terminal anthc– ligand and a 1,10-phen ligand in a chelating fashion. Detailed direct-current and alternating-current susceptibility measurements showed no slow magnetism relaxation phenomenon was observed for 1.
文摘The structure, magnetization, and magnetocrystalline anisotropy wereinvestigated using X-ray diffraction, vibrating sample magnetometer, and AC susceptibility-meter Itis found that the microstructure of (Sm_(0.5)Nd_(0.5))_2(Fe_(1-x)Co_x)_(17) alloys is an(Sm,Nd)_2(Fe,Co)_(17) phase with the rhombohedral Th_2Zn_(17)-type structure. The Curie temperatureT_c increases with the Co concentration increasing, and the magnetization first increases as the Cocontent increases in (Sm_(0.5)Nd_(0.5))_2(Fe_(1-x)Co_x)_(17) alloys and then decreases slowly. Theeasy magnetization direction (EMD) of (Sm_(0.5)Nd_(0.5))_2(Fe_(0.25)Co_(0.75))_(17) is along thec-axis and a strong enhancement of the crystalline anisotropy energy constant K is produced by theaddition of some Co atoms. The anisotropy energy constant reaches the maximum when x = 0.75 and thendecreases slowly with the Co content further increasing. The(Sm_(0.5)Nd_(0.5))_2(Fe_(0.25)Co_(0.75))_(17) compound is an optical candidate for the new permanentmagnet, which possesses a high magnetization, a high Curie temperature, and a large anisotropy.
基金Supported by Higher Education Science Foundation of Jiangsu Province(No.15KJB150031)State Key Laboratory of Structural Chemistry Fund(No.20150009)+1 种基金Yangzhou University for the start-up grantthe Priority Academic Program Development of Jiangsu Higher Education Institutions
文摘A new ternary neodymium zirconium sulfide Nd_2ZrS_5 was synthesized by high-temperature solid-state reaction and structurally characterized by single-crystal X-ray diffraction. It crystallizes in the orthorhombic space group Pnma(No. 62) belonging to the Y_2HfS_5 structure-type with a = 11.461(4), b = 8.009(3), c = 7.315(3) A, Z = 2 and V = 671.5(4)A3. Its structure features NdS_8 and ZrS_7 polyhedra-constructed a 3-D network. The data of magnetic susceptibility indicate its antiferromagnetic-like behavior without magnetic order down to 2 K.
基金financially supported by the National Natural Science Foundation of China(21571093)the Science and Technology Project of Henan Province(No.162106000025)
文摘Two new coordination polymers,namely,{[Cd(1.5)(bc)2(HL)](13)H2O}(2n)(1) and [Mn(ip)(H2L)(H2O)]n(2)(H2L = 3-(1 H-pyrazol-4-yl)-5-(pyridin-2-yl)-1,2,4-triazole,Hbc = benzoic acid,H2 ip = isophthalic acid) were constructed by solvothermal reaction.The compounds were characterized by elemental analysis,FT-IR spectroscopy,and single-crystal X-ray diffraction.Compound 1 displays a two-dimensional plane structure consisting of [Cd3(bc)2(HL)] subunits.Compound 2 possesses a one-dimensional chain structure and is further extended into a 3-D supramolecular architecture via hydrogen bonds.Moreover,photoluminescence studies showed compound 1 exhibits luminescent emissions with emission maxima at 375 nm.Magnetic susceptibility measurements of 2 indicate that domain antiferromagnetic interactions exist between Mn(Ⅱ) ions.In addition,thermogravimetric properties of 1 and 2 were also measured.
基金National Natural Science FOundation of China!59571014National Natural Science FOundation of China!59725103National Natur
文摘The alloy with nominal composition Sm_2(Fe0.94Ti0.06)17 is prepared by arc-melting, hydrogenation and nitrogenation processes. The Sm_2(Fe0.94Ti0.06)17 alloy has a single phase of Sm_3(Fe, Ti)29 with the Nd_3(Fe, Ti)29-type structure. The corresponding hydride phase with the same phase structure of the parent alloy was formed after a hydrogen decrepitation (HD) process at 300℃. The hydrogenation at 800℃ mainly shows a HDDR process. The HD and nitrogenation at 500℃ result in increasing the Curie temperature of the alloy by 72℃ and by 158℃ due to lattice expansions, respectively. The anisotropic and isotropic Sm_3(Fe. Ti)29N_y magnets are obtained after HD, HDDR and the consequent nitrogenation, respectively. The optimum magnetic properties of Sm_3(Fe, Ti)29N_y powders achieved in the above two processes are: (i) B_r=0;82 T, _iH_c=4.48 kA/cm. (BH)_max=54.3 kJ/m^3, (ii) B_r=0.68 T, _iH_c=8.14 kA/cm, (BH)max=66.4 kJ/m^3.
基金Project supported by the National Basic Research Program of China(Grant No.2012CB619401)
文摘The crystal structure,magnetization,and spontaneous magnetostriction of ferromagnetic Laves phase Gd Fe2 compound have been investigated.High resolution synchrotron x-ray diffraction(XRD) analysis shows that Gd Fe2 has a lower cubic symmetry with easy magnetization direction(EMD) along [100] below Curie temperature TC.The replacement of Gd with a small amount of Tb changes the EMD to [111].The Curie temperature decreases while the field dependence of the saturation magnetization(Ms) measured in temperature range 5–300 K varies with increasing Tb concentration.Coercivity Hc increases with increasing Tb concentration and decays exponentially as temperature increases.The anisotropy in Gd Fe2 is so weak that some of the rare-earth substitution plays an important role in determining the easy direction of magnetization in GdFe_2.The calculated magnetostrictive constant λ100 shows a small value of 37×10^(-6).This value agrees well with experimental data 30×10^(-6).Under a relatively small magnetic field,GdFe_2 exhibits a V-shaped positive magnetostriction curve.When the field is further increased,the crystal exhibits a negative magnetostriction curve.This phenomenon has been discussed in term of magnetic domain switching.Furthermore,magnetostriction increases with increasing Tb concentration.Our work leads to a simple and unified mesoscopic explanation for magnetostriction in ferromagnets.It may also provide insight for developing novel functional materials.