The compound ingots of Pr0.15TbxDy0.85-xFe2 (x=0 to 0.85) were prepared by arc melting in a water Cu boat using arc furnace under a purified Ar atmosphere. Appropriate annealing (850℃, 100 h) can obtain single Laves ...The compound ingots of Pr0.15TbxDy0.85-xFe2 (x=0 to 0.85) were prepared by arc melting in a water Cu boat using arc furnace under a purified Ar atmosphere. Appropriate annealing (850℃, 100 h) can obtain single Laves phase compound. The magnetostriction for these systems will rise obviously when partially substituted Tb or Dy by Pr.展开更多
The possible geometries of Fe(HCN)n (n = 1~6) compounds were studied by using + DFT/UB3LYP/6-31G(2df) method. The structure and ground state ...The possible geometries of Fe(HCN)n (n = 1~6) compounds were studied by using + DFT/UB3LYP/6-31G(2df) method. The structure and ground state of each fragmental ion are C∞v (4Σ+ or Σ ), D∞h (4Σg ), D3 (4A1 ), C2 or Td or C3v (4A1), and D3 (4A1 ) or C4 ( A1 ) sequentially 6 + + ′ ′ ′ 2 ′ h v h v with n = 1~5. For the compound Fe(HCN)6 , the possible geometry was not obtained. The + sequential incremental interaction energy (–?(?E)), dissociation energy (?D0), enthalpy (–?(?H)) and Gibbs free energy (–?(?G)), and frequencies for HCN-Fe(HCN)n + -1 were also calculated, and the results are all in good agreement with the experiments. The bond length of Fe–N is lengthened with the increase of cluster size, and the strength of Fe+–N coordination bond varies nonmon- tonically as increasing the number of ligands. The Fe+–N bond of Fe(HCN)2 is the strongest in all + compounds.展开更多
The crystallographic structure and intrinsic magnetic properties have been investigated in the RTiFe_(11), RTiCo_(11) and RTi(Fe_(1-X)Ni_X)_(11) compounds,where R represents Nd,Sm,Gd,Tb,Dy,Ho,Er and Y.Neutron diffract...The crystallographic structure and intrinsic magnetic properties have been investigated in the RTiFe_(11), RTiCo_(11) and RTi(Fe_(1-X)Ni_X)_(11) compounds,where R represents Nd,Sm,Gd,Tb,Dy,Ho,Er and Y.Neutron diffraction and Mossbauer spectra analyses have been used to study the nuclear and magnetic structure of these compounds.the Fe,Co,Ni and Ti atoms are found to exhibit strong site preference with f and j sites fa- voring Fe,Co and Ni atoms and the i site Ti atoms.Two different types of magnetic behavior were observed in the RTiFe_(11) and RTiCo_(11) compounds.In the former,the interatomic distance and the number of nearest neighbor atoms play essential roles.In particular,anomalous thermal expansion behavior is presented in RTiFe_(11).In the latter,the magnetic properties are essentially determined by the modification of the cobalt electronic configuration brought about by the transfer of rare earth conduction electrons to the transition 3d band.The saturation magnetization,Curie temperature and magnetocrystalline anisotropy data of RTiFe_(11), RTiCo_(11)and YTi(Fe_(1-X)Ni_X)_(11)are presented.A tempt to improve the intrinsic magnetic properties in RTiFe_(11)has been made,and the results are reported.On the basis of the crystalline field theory by using a single-ion model,the anisotropy constants and their temperature dependence of the R ions have been calcu- lated,which helps explain the spin reorientation observed in RTiFe_(11).展开更多
The Mn Fe P0.56Si0.44 compound is investigated by x-ray diffraction, magnetic measurements, and x-ray absorption fine structure spectroscopy. It crystallizes in Fe2P-type structure with the lattice parameters a = b = ...The Mn Fe P0.56Si0.44 compound is investigated by x-ray diffraction, magnetic measurements, and x-ray absorption fine structure spectroscopy. It crystallizes in Fe2P-type structure with the lattice parameters a = b = 5.9823(0) and c = 3.4551(1) and undergoes a first-order phase transition at the Curie temperature of 255 K. The Fe K edge and Mn K edge x-ray absorption fine structure spectra show that Mn atoms mainly reside at 3g sites, while 3f sites are occupied by Fe atoms. The distances between the absorbing Fe atom and the first and second nearest neighbor Fe atoms in a 3f-layer shift from 2.65 and 4.01 in the ferromagnetic state to 2.61 and 3.96 in the paramagnetic phase. On the other hand, the distance between the 3g-layer and 3f-layer changes a little as 2.66 –2.73 below the Curie temperature and2.68 –2.75 above it.展开更多
In this article, our recent progress concerning the effects of atomic substitution, magnetic field, and temperature on the magnetic and magnetocaloric properties of the LaFe13-xAlx compounds are reviewed. With an incr...In this article, our recent progress concerning the effects of atomic substitution, magnetic field, and temperature on the magnetic and magnetocaloric properties of the LaFe13-xAlx compounds are reviewed. With an increase of the aluminum content, the compounds exhibit successively an antiferromagnetic (AFM) state, a ferromagnetic (FM) state, and a mictomagnetic state. Furthermore, the AFM coupling of LaFe13 -xAlx can be converted to an FM one by substituting Si for A1, Co for Fe, and magnetic rare-earth R for La, or introducing interstitial C or H atoms. However, low doping levels lead to FM clusters embedded in an AFM matrix, and the resultant compounds can undergo, under appropriate applied fields, first an AFM-FM and then an FM-AFM phase transition while heated, with significant magnetic relaxation in the vicinity of the transition temperature. The Curie temperature of LaFe13-xAlx can be shifted to room temperature by choosing appropriate contents of Co, C, or H, and a strong magnetocaloric effect can be obtained around the transition temperature. For example, for the LaFel 1.5All.5Co.2Hl.o compound, the maximal entropy change reaches 13.8 J.kg-1.K-1 for a field change of 0-5 T, occurring around room temperature. It is 42% higher than that of Gd, and therefore, this compound is a promising room-temperature magnetic refrigerant.展开更多
Micro-scale Al-Zn-Mg/Fe composite powders (MAF) with high reactivity and good storage properties were prepared by reducing iron onto the surface of Al-Zn-Mg alloy powders. Experimental results show that MAF as advance...Micro-scale Al-Zn-Mg/Fe composite powders (MAF) with high reactivity and good storage properties were prepared by reducing iron onto the surface of Al-Zn-Mg alloy powders. Experimental results show that MAF as advanced zero-valent iron are highly effective for degradation of chlorinated organic compounds. The efficiency of degradation for carbon tetrachloride and perchloroethylene is higher than 99% within a period of 2 h. The efficiency of degradation for trichloroethylene by MAF after storing for one month is equivalent to that by freshly prepared nano-size zero-valent iron particles.展开更多
The structure, Curie temperature and magnetostriction of Pr0.15Tb0.30Dy0.55Fe1.85Cx (x=0-0.1) compounds were investigated by X-ray diffraction, a vibrating sample magnetometer and a standard strain technique. All the ...The structure, Curie temperature and magnetostriction of Pr0.15Tb0.30Dy0.55Fe1.85Cx (x=0-0.1) compounds were investigated by X-ray diffraction, a vibrating sample magnetometer and a standard strain technique. All the samples show entirely MgCu2-type Laves phase structure. The lattice parameter and Curie temperature increase with C content increasing. The magnetostriction at high magnetic field shows maximum value at x=0.05.展开更多
The structure and magnetic properties of Dy2AlFe12Mn4 compound have been investigated by means of X-ray diffraction and magnetization measurements. The Dy2AlFe12Mn4 compound has a hexagonal Th2Ni17-type structure. Neg...The structure and magnetic properties of Dy2AlFe12Mn4 compound have been investigated by means of X-ray diffraction and magnetization measurements. The Dy2AlFe12Mn4 compound has a hexagonal Th2Ni17-type structure. Negative thermal expansion was found in Dy2AlFe12Mn4 compound from 229 to 280 K by X-ray dilatometry. The coefficient of the average thermal expansion is α^- =-3.8×10^-5 K^-1. The magnetostrictive deformations from 105 to 270 K have been calculated by means of the differences between the experimental values of the lattice parameters and the corresponding values extrapolated from the paramagnetic range. The result shows that the spontaneous volume magnetostrictive deformation ωs decreases from 6.2 × 10^-3 to near zero with the temperature increasing from 105 to 270 K, the spontaneous linear magnetostrictive deformation λc along the c axis is much larger than the spontaneous linear magnetostrictive deformation λa in basal-plane at the same temperature except close to 249 K.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
Structural, thermal expansion, and magnetic properties of the Dy_2Fe_(16)Cr compound are investigated by means of x-ray diffraction and magnetization measurements. The Dy_2Fe_(16)Cr compound has a hexagonal Th_2Ni_(17...Structural, thermal expansion, and magnetic properties of the Dy_2Fe_(16)Cr compound are investigated by means of x-ray diffraction and magnetization measurements. The Dy_2Fe_(16)Cr compound has a hexagonal Th_2Ni_(17)-type structure. There exists a negative thermal expansion resulting from a strong spontaneous magnetostriction in the magnetic state of the Dy_2Fe_(16)Cr compound. The average thermal expansion coefficient is-0.794 × 10^(-5)/K in the temperature range 292–407 K. The spontaneous magnetostrictive deformation and the Curie temperature are discussed.展开更多
The structure and magnetic properties of Dy2AlFe14Mn2 compound were investigated by X-ray diffractometry and magnetization measurements.Dy2AlFe14Mn2 compound has a hexagonal Th2Ni17-type structure.Zero thermal expansi...The structure and magnetic properties of Dy2AlFe14Mn2 compound were investigated by X-ray diffractometry and magnetization measurements.Dy2AlFe14Mn2 compound has a hexagonal Th2Ni17-type structure.Zero thermal expansion and negative thermal expansion were found in Dy2AlFe14Mn2 compound in the temperature range from 184 to 264 K,and from 264 to 383 K,respectively,by X-ray dilatometry.The spontaneous magnetostrictive deformations from 104 to 400 K were calculated.The results show that the spontaneous volume magnetostrictive deformation increases firstly with increasing temperature,and then decreases with further increasing temperature.展开更多
DyTiFe_(11) compound is a ferromagnetic substance.It has tetragonal body-centered ThMn_(12)-type crystallographic structure.At room temperature,the easy magnetization direction is the c-axis.A spin reorientation begin...DyTiFe_(11) compound is a ferromagnetic substance.It has tetragonal body-centered ThMn_(12)-type crystallographic structure.At room temperature,the easy magnetization direction is the c-axis.A spin reorientation begins to appear at about 175K.The contribution of Fe sublattice to magnetocrystalline anisotropy was determined by experiments and that of Dy sublattice was obtained by using single ion model calculation.Results show that the spin reorientation arises from the competition of anisotropy between Fe and Dy sublattices.展开更多
The self-consistent ab initio calculations based on the density functional theory approach using the full potential linear augmented plane wave method are performed to investigate both the electronic and magnetic prop...The self-consistent ab initio calculations based on the density functional theory approach using the full potential linear augmented plane wave method are performed to investigate both the electronic and magnetic properties of the NiFe compound. Polarized spin within the framework of the ferromagnetic state between magnetic ions is considered. Also, magnetic moments considered to lie along (001) axes are computed. The Monte Carlo simulation is used to study the magnetic properties of NiFe. The transition temperature To, hysteresis loop, coercive field and remanent magnetization of the NiFe compound are obtained using the Monte Carlo simulation.展开更多
The structural and magnetostrictive properties of (CexTb1-x)0.5Pr0.5Fe_2 were investigated. Ceconcentration must exceed x=0.6 in order to obtain the pure Laves phase. The magnetostriction and anisotropy constant incr...The structural and magnetostrictive properties of (CexTb1-x)0.5Pr0.5Fe_2 were investigated. Ceconcentration must exceed x=0.6 in order to obtain the pure Laves phase. The magnetostriction and anisotropy constant increase with the Tb-content in this system. The anisotropy value of PrFe_2 is lower than that of isostructural DyFe_2. From the X-ray step-scanned data we found that λ_111 of PrFe_2 is 1310x10^-6. A large increase of magnetostriction can be observed under a small prestress of 6 MP_a for Ce_0.5Pr_0.5Fe_2.展开更多
A systematic study of syntheses and magnetic properties of the Nd_3Fe_(29-x)Cr_x (x=4.5, 4.7, 5.0, and 5.5) compounds has been performed. The single-phase compounds of Nd_3Fe_(29-x)Cr_x can be formed in the range 4.5...A systematic study of syntheses and magnetic properties of the Nd_3Fe_(29-x)Cr_x (x=4.5, 4.7, 5.0, and 5.5) compounds has been performed. The single-phase compounds of Nd_3Fe_(29-x)Cr_x can be formed in the range 4.5≤ x ≤ 5.5. The Curie temperature T_C, the saturation magnetization M_s at 4.2 K, the anisotropy field H_A at 4.2 K and room temperature. and the intra-sublattice exchange coupling parameter j_(FeFe) at 4.2 K for the Nd_3Fe_(29-x)Cr_x compounds decrease with increasing Cr composition from x=4.5 to 5.5, respectively. Nitrogenation and carbonation, unlike hydrogenation. result mainly in improvements of the Curie temperature, the saturation magnetization and the anisotropy field at 4.2 K and room temperature for the Nd_3Fe_(29-x)Cr_x compounds compared with their parent compounds.展开更多
The temperature dependent magnetization of the (Ce,Nd) 2(Fe,Si,Mn) 17 intermetallic compounds were measured and analyzed by molecular field theory (MFT). The relationship between T C and the intrasublattic...The temperature dependent magnetization of the (Ce,Nd) 2(Fe,Si,Mn) 17 intermetallic compounds were measured and analyzed by molecular field theory (MFT). The relationship between T C and the intrasublattice coupling interactions was discussed. The two sublattice MFT model can well describe the temperature dependence of the magnetization for all the compounds investigated. Ce ion in (Ce,Nd) 2Fe 17 compounds does not simply dilute the magnetic structure, but is likely present in a mixed valence state. The substitution of Si for Fe strongly raises T C and the mean Fe moment remains unchanged for Ce 2(Si,Fe) 17 compounds, and the 3d exchange coupling constant J FF increases linearly. Mn decreases T C of Nd 2(Mn, Fe) 17 compound by reducing J FF .展开更多
The melting behavior,solid state phase transformation and structure of pseudo-ternary compounds Nd_2(Fe_(1-x)Ni_x)_(14)B and Pr_2(Co_(1-y)Ni_y)_(14)B were studied using differential thermal analysis,optical microscopy...The melting behavior,solid state phase transformation and structure of pseudo-ternary compounds Nd_2(Fe_(1-x)Ni_x)_(14)B and Pr_2(Co_(1-y)Ni_y)_(14)B were studied using differential thermal analysis,optical microscopy X-ray diffraction,and electron probe micro-analysis techniques.At high temperature,eutectoid decomposition R_2(Ni,M)_(17)→R(Ni,M)_5+x-Ni(M) takes place in these two pseudo-ternary compounds,in the composition range x=0.6~1.0 and y=0.3~1.0,respectively.When x(or y)≤0.2,both Nd_2(Fe_(1-x)Ni_x)_(14)B and Pr_2(Co_(1-y)Ni_y)_(14)B are single phase tetragonal.The phase constitutents of these two systems at room tempera- ture are similar in the composition range 0.6≤x(or y)≤1.0.展开更多
The formation of Fe-N compounds by laser nitriding in an atmospheric ambient was reported. By CW-CO2 laser irradiation on pure ferrite iron in the atmospheric ambient, Fe-N compounds (including Fe2N, .Fe3AT and Fe4N) ...The formation of Fe-N compounds by laser nitriding in an atmospheric ambient was reported. By CW-CO2 laser irradiation on pure ferrite iron in the atmospheric ambient, Fe-N compounds (including Fe2N, .Fe3AT and Fe4N) are formed as a result of a laser-enhanced and temperature-enhanced reactions. The samples were analyzed with X-ray diffraction. It is found that the laser power density, scanning speed and nitrogen temperature are the main factors influencing the formation of Fe-N compounds. Nitrogen can be activated by pre-heating at some temperature. Nitrogen activation and sample surface melting by CW-CO2 laser greatly enhance the reaction between the sample surface and nitrogen beam. After annealing at 500℃for 3h, some Fe2N and Fe3N converted into more stable Fe4N.展开更多
基金the Natural Science Foundation of Hebei Province 596028 and the National NaturalScience Foundation of China No.59871062.
文摘The compound ingots of Pr0.15TbxDy0.85-xFe2 (x=0 to 0.85) were prepared by arc melting in a water Cu boat using arc furnace under a purified Ar atmosphere. Appropriate annealing (850℃, 100 h) can obtain single Laves phase compound. The magnetostriction for these systems will rise obviously when partially substituted Tb or Dy by Pr.
基金This research was supported by the National Natural Science Foundation of China (20273013 20303002)+1 种基金 the Key Foundation of Fujian Province (K02012) the Foundation of State Key Laboratory of Structural Chemistry (020051) and of Fuzhou University
文摘The possible geometries of Fe(HCN)n (n = 1~6) compounds were studied by using + DFT/UB3LYP/6-31G(2df) method. The structure and ground state of each fragmental ion are C∞v (4Σ+ or Σ ), D∞h (4Σg ), D3 (4A1 ), C2 or Td or C3v (4A1), and D3 (4A1 ) or C4 ( A1 ) sequentially 6 + + ′ ′ ′ 2 ′ h v h v with n = 1~5. For the compound Fe(HCN)6 , the possible geometry was not obtained. The + sequential incremental interaction energy (–?(?E)), dissociation energy (?D0), enthalpy (–?(?H)) and Gibbs free energy (–?(?G)), and frequencies for HCN-Fe(HCN)n + -1 were also calculated, and the results are all in good agreement with the experiments. The bond length of Fe–N is lengthened with the increase of cluster size, and the strength of Fe+–N coordination bond varies nonmon- tonically as increasing the number of ligands. The Fe+–N bond of Fe(HCN)2 is the strongest in all + compounds.
文摘The crystallographic structure and intrinsic magnetic properties have been investigated in the RTiFe_(11), RTiCo_(11) and RTi(Fe_(1-X)Ni_X)_(11) compounds,where R represents Nd,Sm,Gd,Tb,Dy,Ho,Er and Y.Neutron diffraction and Mossbauer spectra analyses have been used to study the nuclear and magnetic structure of these compounds.the Fe,Co,Ni and Ti atoms are found to exhibit strong site preference with f and j sites fa- voring Fe,Co and Ni atoms and the i site Ti atoms.Two different types of magnetic behavior were observed in the RTiFe_(11) and RTiCo_(11) compounds.In the former,the interatomic distance and the number of nearest neighbor atoms play essential roles.In particular,anomalous thermal expansion behavior is presented in RTiFe_(11).In the latter,the magnetic properties are essentially determined by the modification of the cobalt electronic configuration brought about by the transfer of rare earth conduction electrons to the transition 3d band.The saturation magnetization,Curie temperature and magnetocrystalline anisotropy data of RTiFe_(11), RTiCo_(11)and YTi(Fe_(1-X)Ni_X)_(11)are presented.A tempt to improve the intrinsic magnetic properties in RTiFe_(11)has been made,and the results are reported.On the basis of the crystalline field theory by using a single-ion model,the anisotropy constants and their temperature dependence of the R ions have been calcu- lated,which helps explain the spin reorientation observed in RTiFe_(11).
基金supported by the National Natural Science Foundation of China(Grant Nos.51461035,51161017,and 11404176)the Scientific Research Projects of the Higher Educational Department of Inner Mongolian Autonomous Region,China(Grant No.NJZZ14033)The XAFS measurement was performed under the approval of Photon Factory Program Advisory Committee(Proposal Nos.2012G095 and 2014G047)
文摘The Mn Fe P0.56Si0.44 compound is investigated by x-ray diffraction, magnetic measurements, and x-ray absorption fine structure spectroscopy. It crystallizes in Fe2P-type structure with the lattice parameters a = b = 5.9823(0) and c = 3.4551(1) and undergoes a first-order phase transition at the Curie temperature of 255 K. The Fe K edge and Mn K edge x-ray absorption fine structure spectra show that Mn atoms mainly reside at 3g sites, while 3f sites are occupied by Fe atoms. The distances between the absorbing Fe atom and the first and second nearest neighbor Fe atoms in a 3f-layer shift from 2.65 and 4.01 in the ferromagnetic state to 2.61 and 3.96 in the paramagnetic phase. On the other hand, the distance between the 3g-layer and 3f-layer changes a little as 2.66 –2.73 below the Curie temperature and2.68 –2.75 above it.
基金Project supported by the National Natural Science Foundation of Chinathe Key Research Program of the Chinese Academy of Sciences+1 种基金the National Basic Research Program of Chinathe National High Technology Research and Development Program of China
文摘In this article, our recent progress concerning the effects of atomic substitution, magnetic field, and temperature on the magnetic and magnetocaloric properties of the LaFe13-xAlx compounds are reviewed. With an increase of the aluminum content, the compounds exhibit successively an antiferromagnetic (AFM) state, a ferromagnetic (FM) state, and a mictomagnetic state. Furthermore, the AFM coupling of LaFe13 -xAlx can be converted to an FM one by substituting Si for A1, Co for Fe, and magnetic rare-earth R for La, or introducing interstitial C or H atoms. However, low doping levels lead to FM clusters embedded in an AFM matrix, and the resultant compounds can undergo, under appropriate applied fields, first an AFM-FM and then an FM-AFM phase transition while heated, with significant magnetic relaxation in the vicinity of the transition temperature. The Curie temperature of LaFe13-xAlx can be shifted to room temperature by choosing appropriate contents of Co, C, or H, and a strong magnetocaloric effect can be obtained around the transition temperature. For example, for the LaFel 1.5All.5Co.2Hl.o compound, the maximal entropy change reaches 13.8 J.kg-1.K-1 for a field change of 0-5 T, occurring around room temperature. It is 42% higher than that of Gd, and therefore, this compound is a promising room-temperature magnetic refrigerant.
文摘Micro-scale Al-Zn-Mg/Fe composite powders (MAF) with high reactivity and good storage properties were prepared by reducing iron onto the surface of Al-Zn-Mg alloy powders. Experimental results show that MAF as advanced zero-valent iron are highly effective for degradation of chlorinated organic compounds. The efficiency of degradation for carbon tetrachloride and perchloroethylene is higher than 99% within a period of 2 h. The efficiency of degradation for trichloroethylene by MAF after storing for one month is equivalent to that by freshly prepared nano-size zero-valent iron particles.
基金The work was financially supported by the National Science Foundation of Hebei Province(No.E2006000063)and Foundation of Hebei Education Department(No.2005216).
文摘The structure, Curie temperature and magnetostriction of Pr0.15Tb0.30Dy0.55Fe1.85Cx (x=0-0.1) compounds were investigated by X-ray diffraction, a vibrating sample magnetometer and a standard strain technique. All the samples show entirely MgCu2-type Laves phase structure. The lattice parameter and Curie temperature increase with C content increasing. The magnetostriction at high magnetic field shows maximum value at x=0.05.
基金This project was financially supported by the National Natural Science Foundation of China (No. 50271022)the Excellent Yong Teachers Program ofMOE of China (No. 1999), and the Natural Science Foundation of Tianjin City (No. 043602011).]
文摘The structure and magnetic properties of Dy2AlFe12Mn4 compound have been investigated by means of X-ray diffraction and magnetization measurements. The Dy2AlFe12Mn4 compound has a hexagonal Th2Ni17-type structure. Negative thermal expansion was found in Dy2AlFe12Mn4 compound from 229 to 280 K by X-ray dilatometry. The coefficient of the average thermal expansion is α^- =-3.8×10^-5 K^-1. The magnetostrictive deformations from 105 to 270 K have been calculated by means of the differences between the experimental values of the lattice parameters and the corresponding values extrapolated from the paramagnetic range. The result shows that the spontaneous volume magnetostrictive deformation ωs decreases from 6.2 × 10^-3 to near zero with the temperature increasing from 105 to 270 K, the spontaneous linear magnetostrictive deformation λc along the c axis is much larger than the spontaneous linear magnetostrictive deformation λa in basal-plane at the same temperature except close to 249 K.
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Supported by the National Natural Science Foundation of China under Grant Nos 50871074 and 61474082
文摘Structural, thermal expansion, and magnetic properties of the Dy_2Fe_(16)Cr compound are investigated by means of x-ray diffraction and magnetization measurements. The Dy_2Fe_(16)Cr compound has a hexagonal Th_2Ni_(17)-type structure. There exists a negative thermal expansion resulting from a strong spontaneous magnetostriction in the magnetic state of the Dy_2Fe_(16)Cr compound. The average thermal expansion coefficient is-0.794 × 10^(-5)/K in the temperature range 292–407 K. The spontaneous magnetostrictive deformation and the Curie temperature are discussed.
基金Project(50271022) supported by the National Natural Science Foundation of ChinaProject(1999) supported by the Excellent Yong Teachers Program of MOEProject(043602011) supported by the Natural Science Foundation of Tianjin City,China
文摘The structure and magnetic properties of Dy2AlFe14Mn2 compound were investigated by X-ray diffractometry and magnetization measurements.Dy2AlFe14Mn2 compound has a hexagonal Th2Ni17-type structure.Zero thermal expansion and negative thermal expansion were found in Dy2AlFe14Mn2 compound in the temperature range from 184 to 264 K,and from 264 to 383 K,respectively,by X-ray dilatometry.The spontaneous magnetostrictive deformations from 104 to 400 K were calculated.The results show that the spontaneous volume magnetostrictive deformation increases firstly with increasing temperature,and then decreases with further increasing temperature.
文摘DyTiFe_(11) compound is a ferromagnetic substance.It has tetragonal body-centered ThMn_(12)-type crystallographic structure.At room temperature,the easy magnetization direction is the c-axis.A spin reorientation begins to appear at about 175K.The contribution of Fe sublattice to magnetocrystalline anisotropy was determined by experiments and that of Dy sublattice was obtained by using single ion model calculation.Results show that the spin reorientation arises from the competition of anisotropy between Fe and Dy sublattices.
文摘The self-consistent ab initio calculations based on the density functional theory approach using the full potential linear augmented plane wave method are performed to investigate both the electronic and magnetic properties of the NiFe compound. Polarized spin within the framework of the ferromagnetic state between magnetic ions is considered. Also, magnetic moments considered to lie along (001) axes are computed. The Monte Carlo simulation is used to study the magnetic properties of NiFe. The transition temperature To, hysteresis loop, coercive field and remanent magnetization of the NiFe compound are obtained using the Monte Carlo simulation.
基金Natural Science of Hebei Province!(No. 596028)National Natural Science Foundation of China!(No. 59871062).
文摘The structural and magnetostrictive properties of (CexTb1-x)0.5Pr0.5Fe_2 were investigated. Ceconcentration must exceed x=0.6 in order to obtain the pure Laves phase. The magnetostriction and anisotropy constant increase with the Tb-content in this system. The anisotropy value of PrFe_2 is lower than that of isostructural DyFe_2. From the X-ray step-scanned data we found that λ_111 of PrFe_2 is 1310x10^-6. A large increase of magnetostriction can be observed under a small prestress of 6 MP_a for Ce_0.5Pr_0.5Fe_2.
文摘A systematic study of syntheses and magnetic properties of the Nd_3Fe_(29-x)Cr_x (x=4.5, 4.7, 5.0, and 5.5) compounds has been performed. The single-phase compounds of Nd_3Fe_(29-x)Cr_x can be formed in the range 4.5≤ x ≤ 5.5. The Curie temperature T_C, the saturation magnetization M_s at 4.2 K, the anisotropy field H_A at 4.2 K and room temperature. and the intra-sublattice exchange coupling parameter j_(FeFe) at 4.2 K for the Nd_3Fe_(29-x)Cr_x compounds decrease with increasing Cr composition from x=4.5 to 5.5, respectively. Nitrogenation and carbonation, unlike hydrogenation. result mainly in improvements of the Curie temperature, the saturation magnetization and the anisotropy field at 4.2 K and room temperature for the Nd_3Fe_(29-x)Cr_x compounds compared with their parent compounds.
文摘The temperature dependent magnetization of the (Ce,Nd) 2(Fe,Si,Mn) 17 intermetallic compounds were measured and analyzed by molecular field theory (MFT). The relationship between T C and the intrasublattice coupling interactions was discussed. The two sublattice MFT model can well describe the temperature dependence of the magnetization for all the compounds investigated. Ce ion in (Ce,Nd) 2Fe 17 compounds does not simply dilute the magnetic structure, but is likely present in a mixed valence state. The substitution of Si for Fe strongly raises T C and the mean Fe moment remains unchanged for Ce 2(Si,Fe) 17 compounds, and the 3d exchange coupling constant J FF increases linearly. Mn decreases T C of Nd 2(Mn, Fe) 17 compound by reducing J FF .
基金the National Natural Science Fundation of China.
文摘The melting behavior,solid state phase transformation and structure of pseudo-ternary compounds Nd_2(Fe_(1-x)Ni_x)_(14)B and Pr_2(Co_(1-y)Ni_y)_(14)B were studied using differential thermal analysis,optical microscopy X-ray diffraction,and electron probe micro-analysis techniques.At high temperature,eutectoid decomposition R_2(Ni,M)_(17)→R(Ni,M)_5+x-Ni(M) takes place in these two pseudo-ternary compounds,in the composition range x=0.6~1.0 and y=0.3~1.0,respectively.When x(or y)≤0.2,both Nd_2(Fe_(1-x)Ni_x)_(14)B and Pr_2(Co_(1-y)Ni_y)_(14)B are single phase tetragonal.The phase constitutents of these two systems at room tempera- ture are similar in the composition range 0.6≤x(or y)≤1.0.
文摘The formation of Fe-N compounds by laser nitriding in an atmospheric ambient was reported. By CW-CO2 laser irradiation on pure ferrite iron in the atmospheric ambient, Fe-N compounds (including Fe2N, .Fe3AT and Fe4N) are formed as a result of a laser-enhanced and temperature-enhanced reactions. The samples were analyzed with X-ray diffraction. It is found that the laser power density, scanning speed and nitrogen temperature are the main factors influencing the formation of Fe-N compounds. Nitrogen can be activated by pre-heating at some temperature. Nitrogen activation and sample surface melting by CW-CO2 laser greatly enhance the reaction between the sample surface and nitrogen beam. After annealing at 500℃for 3h, some Fe2N and Fe3N converted into more stable Fe4N.