First-principles study on electronic structure, magnetic and dielectric properties of Cr-doped Fe_3C

The first-principles calculations were performed to investigate the electronic structure, magnetic and dielectric properties of Cr-doped Fe_3C, in comparison to those of pure Fe_3C and Cr_3C. The obtained results show that the thermodynamic stability of Crdoped Fe_3C becomes weaker in terms of the larger formation enthalpy, on the contrary, the metallicity and covalency are found to strengthen to some extent. The magnetic moments of Fe_3C, Fe_(11)CrC_4(g), and Fe_(11)CrC_4(s) are respectively 21.36 μB/cell, 16.92 μB/cell, and 17.62 μB/cell, and in Fe_(11)CrC4(g) and Fe_(11)CrC_4(s), the Fe of Wyckoff positions of 8d and 4c is substituted by Cr. The local magnetic moment of Cr at 8d site is larger than that at 4c site in the doped structure, which is opposite to that of Fe. In low frequency band, the permittivity follows the ranking of Fe_(11)Cr C_4(s)>Cr_3C>Fe_(11)Cr C_4(g)>Fe_3C. Once exceeding a certain frequency, the sequence will be broken. Besides the electron transition, the polarization of atoms also makes a contribution to the dielectric properties.

Enhanced Magnetic and Dielectric Properties in Low-Content Tb-Doped BiFeO3 Nanoparticles

Bi1-xTbxFeO3 （x = 0, 0.01, 0.03 and 0.05） nanoparticles are synthesized by the sol-gel method. A single phase perovskite rhombohedral structure of all the samples is established from the Rietveld refined XRD patterns. The substitution of Tb^3＋ ions to Bi^3＋ decreases the particle size and enhances the ferromagnetic properties of this system. Interestingly a large maximum magnetization value of 1.73emu/g at 50kOe can be observed in 1% Tb-doped sample at 300 K. The decrease in band gap may result from the reduced particle size, while the leakage current density also decreases, which is mainly explained by the variation of oxygen vacancies.

Effects of(La,Sr) co-doping on electrical conduction and magnetic properties of BiFeO_3 nanoparticles

Multiferroic material as a photovoltaic material has gained considerable attention in recent years.Nanoparticles（NPs）La_（0.1）Bi_（0.9-x）Sr_xFeO_y（LBSF,x = 0,0.2,0.4） with dopant Sr^（2＋）ions were synthesized by the sol–gel method.A systematic change in the crystal structure from rhombohedral to tetragonal upon increasing Sr doping was observed.There is an obvious change in the particle size from 180 nm to 50 nm with increasing Sr substitution into LBFO.It was found that Sr doping effectively narrows the band gap from～2.08 e V to～1.94 e V,while it leads to an apparent enhancement in the electrical conductivity of LBSF NPs,making a transition from insulator to semiconductor.This suggests an effective way to modulate the conductivity of BiFeO_（3-）based multiferroic materials with pure phase by co-doping with La and Sr at the A sites of BiFeO_3.

Effects of Ce^(3+) doping on the structure and magnetic properties of Mn-Zn ferrite fibers

Ce3+-doped Mn-Zn ferrite fibers were successfully prepared by the organic gel-thermal decomposition method from metal salts and citric acid. The composition,structure,and magnetic properties of these ferrite fibers were characterized by X-ray diffraction (XRD),scanning electron microscopy (SEM),and vibrating sample magnetometer (VSM). The results show that Mn0.2Zn0.8Fe2-xCexO4 (x = 0-0.04) fibers are featured with an average grain size of 11.6-12.7 nm,with diameters ranging between 1.0 to 3.5 μm and a high ...

Structures and magnetic properties of nanocomposite CoFe_2O_4-BaTiO_3 fibers by organic gel-thermal decomposition process

The nanocomposite xCoFe2O4-(1-x)BaTiO3(x=0.2,0.3,0.4,0.5,molar fraction) fibers with fine diameters and high aspect ratios(length to diameter ratios) were prepared by the organic gel-thermal decomposition process from citric acid and metal salts.The structures and morphologies of gel precursors and fibers derived from thermal decomposition of the gel precursors were characterized by Fourier transform infrared spectroscopy,X-ray diffractometry and scanning electron microscopy.The magnetic properties of the nanocomposite fibers were measured by vibrating sample magnetometer.The nanocomposite fibers consisting of ferrite(CoFe2O4) and perovskite(BaTiO3) are formed at the calcination temperature of 900 ℃ for 2 h.The average grain sizes of CoFe2O4 and BaTiO3 in the nanocomposite fibers increase from 25 to 65 nm with the calcination temperature from 900 to 1 180 ℃.The single fiber constructed from these nanograins of CoFe2O4 and BaTiO3 has a necklace-like morphology.The saturation magnetization of the nanocomposite 0.4CoFe2O4-0.6BaTiO3 fibers increases with the increase of CoFe2O4 grain size,while the coercivity reaches a maximum value when the average grain size of CoFe2O4 is around the critical single-domain size of 45 nm obtained at 1 000 ℃.The saturation magnetization and remanence of the nanocomposite xCoFe2O4-(1-x)BaTiO3(x=0.2,0.3,0.4,0.5) fibers almost exhibit a linear relationship with the molar fraction of CoFe2O4 in the nanocomposites.

Effects of exchange interaction and spin-fluctuation on the magnetic and magneto-optic properties of NdF_3

The exchange interaction between the electrons in the different magnetic ions and the spin-fluctuation of the magnetic ions exist in the paramagnetic media NdF3. The exchange interaction between the electrons in the different magnetic ions may be equivalent to an effective field Hin that is in direct proportion to the magnetization M. The spin-fluctuation of the magnetic ions leads the coefficient of the effective field to vary with temperature. The effective field is given as Hin = -（0.75 ＋ 0.22T） × 10^-5M in NdF3. When the secondary crystal field effect is taken into account, the magnetic susceptibility and Verdet constant are calculated for NdF3 by means of the effective field Hin and the applied field He. The calculated results are in agreement with the measured ones.

Structural and Magnetic Properties of Sm_3(Fe,Ti)_(29) and Sm_3(Fe,Ti)_(29)X_y (X=H, N) Compounds

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.

Synthesis, Electrical and Magnetic Properties of Fe304 Doped by Dy^3＋

The Dy^3＋ -doped Fe3O4 samples were synthesized by sol-gel method, and the effects of dopant on the electrical and magnetic properties were investigated. According to XRD analysis, the high concentration doping of dysprosium ions in Fe3O4 can not be obtained due to the difference of ionic radius, and Fe^3 ＋ ions are replaced by only a small amount of dysprosium ions. The magnetic property was characterized by VSM. The substitution results in the change of saturation magnetization, which may be due to the complex effects of increasing magnetization resulted from Dy^3＋ substitution and decreasing magnetization resulted from the impurity. The electrical property was characterized by four-probe method. With the increasing eoped content, magnetoresistance also increases, then decreases, and increases again. The spin-polarization of doped samples is lower than that of Fe3O4. Lower spin-polarization results in lower tunneling magnetoresistance. Fortunately, barrier was obtained by the second phase at the same time when sample was synthesized. The increase of appropriate barrier height leads to the change of tunneling magnetoresistance.

Deposition and Magnetic Properties of Fe_3O_4/Fe/Fe_3O_4 Tri-layer Films

The Fe_3O_4/Fe/Fe_3O_4 (MIM) tri-layer films (200 nm/12-93 nm/200 um) were prepared on Si(100) by DC-magnetron reactive-sputtering followed by air- or vacuum-annealing at 280-400℃ for 1.5 h, respectively. Magnetic properties and phases under different sandwich and annealing conditions were studied. In MIM structure, the incorporation of the interlayer iron does increase the magnetization measured under 8 kOe (M_8K), but reduce coercivity (H_c). The H_c of asdeposited films decreases from 354 Oe to 74 Oe; while M_8K increases from 254 to 392 emu/cc. By annealing in air, the whole MIM tri-layer film becomes γ-F_e2O_3, H_c is about 550 O_e and M_8K is around 250 emu/cc. The coercivity mechanism of as-deposited and annealed MIM trilayer films belongs to domain-wall pinning type. δM plots show that when the interlayer Fe thickness is 12 um, the Fe and Fe_3O_4 layers are decoupled in the as-deposited and annealed states; while it is coupled in the as deposited state when the Fe thickness increases to 23 um. Vacuum annealing of the MIM films leads to increase in both coercivity and magnetization, and to enhance the exchange coupling between layers.

Effects of Doping on the Magnetic Properties and Frustration of Hexagonal YMn0.9A0.1O3（A=Al,Fe,and Cu）

The doping effects on the frustration and the magnetic properties in hexagonal compounds ot YMn0.9A0.1O3 （A=A1, Fe and Cu） are investigated. Experimental results indicate that both the non-magnetic and magnetic ion dopants lead to the increase of magnetic moments and the decrease of the absolute value of Curie-Weiss temperature （｜θcw｜）- Compared with pure YMnOa, the geometrical frustration of YMn0.9 A0. 1O3 is greatly suppressed and the magnetic coupling in that exhibits dopant-dependent. In addition, for the doped YMno.gAo.103, the antiferromagnetic transition temperature （TN） is also suppressed slightly, which shows an abnormal dilution effect and it may be ascribed to the reduction of frustration due to the chemical substitution.

MAGNETIC PHASE TRANSITIONS AND MAGNETIC PROPERTIES OF Nd_3(Fe,Mo)_(29) COMPOUND AND ITS NITRIDE

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Low-Temperature Properties of CePt_3P Tuned by Magnetic Field

We present low-temperature magnetization, magnetoresistance and specific heat measurements on the Kondo lattice compound CePt_3P under applied magnetic fields up to 9.0 T. At zero field, CePt_3P exhibits a moderately enhanced Sommerfeld coefficient of electronic specific heat γCe=86 mJ/mol·K^2 as well as two successive magnetic transitions of Ce 4f moments: an antiferromagnetic ordering at T_(N_1) = 3.0 K and a spin reorientation at T_(N_2)=1.9 K. The value of T_(N_1) shifts to lower temperature as magnetic field increases, and it is ultimately suppressed around B_c ～3.0 T at 1.5 K. No evidence of non-Fermi liquid behavior is observed around B_c down to the lowest temperature measured. Moreover, γ decreases monotonously with increasing the magnetic field. On the other hand, the electrical resistivity shows an anomalous temperature dependence ρ∝T^n with the exponent n decreasing monotonously from ～2.6 around B_c down to ～1.7 for B = 9.0 T. The T-B phase diagram constructed from the present experimental results of CePt_3P does not match the quantum criticality scenario of heavy fermion systems.

Controllable Synthesis and Magnetic Properties of Monodisperse Fe_3O_4 Nanoparticles

Magnetite （Fe3O4） nanoparticles with different sizes and shapes are synthesized by the thermal decomposition method. Two approaches, non-injection one-pot and hot-injection methods, are designed to investigate the growth mechanism in detail. It is found that the size and shape of nanoparticles are determined by adjusting the precursor concentration and duration time, which can be well explained by the mechanism based on the LaMer model in our synthetic system. The monodisperse Fe3O4 nanoparticles have a mean diameter from 5nm to 16nm, and shape evolution from spherical to triangular and cubic. The magnetic properties are size-dependent, and Fe3O4 nanoparticles in small size about 5 nm exhibit superparamagnetie properties at room temperature and maximum saturation magnetization approaches to 78 emu/g, whereas Fe3O4 nanoparticles develop ferromagnetic properties when the diameter increases to about 16nm.

Structure and Magnetic Properties of FeCo/Al_2O_3 Nanocomposites

The soft magnetic nanocomposites with equiatomic FeCo particles dispersed in Al2O3 matrix were synthesized via a sol-gel technique combined with H2 reduction method. The samples were characterized by X-ray diffraction, transmission electron microscopy and vibrating sample magnetometer. The FeCo nanoparticles in all the samples have the typical bcc structure. With the decreasing of Al2O3 content, the mean grain size of FeCo in the nanocomposites and the saturation magnetization of the samples increase, while the coercivity of samples increases firstly and then decreases due to different magnetic mechanisms.

Effects of ⅢB transition metals on optoelectronic and magnetic properties of HoMnO_3: A first principles study

The optoelectronic and magnetic properties of pure HoMnO3 and Ho0.67T0.33MnO3 （T = La, Y） alloys in hexagonal phase are theoretically investigated by using the first-principles calculations. The investigations are performed by means of the density functional theory through using the spin polarized generalized gradient approximation plus the Hubbard potential （SPGGA ＋ U, Ueff =3 eV）. The studied material HoMnO3 exhibits two indirect band gaps： 1.58 eV for the spin- up state and 0.72 eV for the spin-down state along the S-G direction within the SPGGA ＋ U approximation. It is found that the band gap of pure HoMnO3 for the spin-up state increases with increasing La and Y dopants. The results show that all of the studied materials have semi-metallic behaviors for the spin-up state and semiconducting character for the spin-down state. The substitutions of La and Y for Ho in HoMnO3 cause the static dielectric constant （ε0） to increase in the x direction but to decrease in the z direction. The calculated optical conductivity spectrum of HoMnO3 in a low energy range is in good agreement with the recent experimental data.

Microstructure and Magnetic Properties of Nd_(8.5)Fe_(77.1)B_(6.4)Co_4Zr_3Nb_(0.5)V_(0.5) Ribbons

Microstructure and magnetic properties of Nd8.5Fe77.1B6.4Co4Zr3Nb0.5V0.5 nanocomposite ribbons were investigated. A fine and uniform grain with 30 nm in average size was achieved for the ribbons annealed at 710 ℃ for 4 min, which enhanced the interaction coupling between grains and improved the magnetic properties. The results of three-dimensional atom probe (3DAP) revealed that V-enriched intergranular phase existed at the grain boundaries, suppressing the grain growth during crystallization process. The remanence and coercivity for annealed ribbons reached to 80 emu·g-1 and 567 kA·m-1, respectively.

Structural,magnetic,and dielectric properties of Ni-Zn ferrite and Bi_(2)O_(3)nanocomposites prepared by the sol-gel method

Ni-Zn ferrite and Bi_(2)O_(3)composites were developed by the sol-gel method.The structural,magnetic,and dielectric properties were studied for all the prepared samples.X-ray diffraction(XRD)was performed to study the crystal structure.The results of field emission scanning electron microscopy(FE-SEM)showed that the addition of Bi_(2)O_(3)can increase the grain size of the Ni-Zn ferrite.Magnetic properties were analyzed by a hysteresis loop test and it was found that the saturation magnetization and coercivity decreased with the increase of Bi_(2)O_(3)ratio.In addition,the dielectric properties of the Ni-Zn ferrite were also improved with the addition of Bi_(2)O_(3).

Synthesis,Crystal Structure and Magnetic Properties of a Coordination Polymer [Ni(C_(10)H_(13)NO_4)(H_2O)_2]_n

A novel organic polycarboxylate N-cyclohexylaziridines-2R,3S-dicarboxylic acid was synthesized and reacted with Ni2（OH）2CO3.As a result,a coordination polymer was obtained.It crystallizes in orthorhombic,space group Pbca with a = 8.6325（10）,b = 10.5414（13）,c = 27.644（3） ,Z = 4,V = 2515.5（5） 3,C20H34N2Ni2O12,Mr = 611.91,Dc = 1.616 g/cm3,μ = 1.562 mm-1,F（000） = 1280,the final R = 0.0320 and wR = 0.0677 for 2854 independent reflections with Rint = 0.0390.Crystal structure shows that the coordination environment around the Ni（Ⅱ） ion can be described as a slightly distorted octahedron.The ligands act as a bridge through the carboxyl O atoms and join the Ni atoms into an infinite 1D chain structure.The 1D chain forms a 2D network through intermolecular O-H…O hydrogen bonds.The magnetic susceptibility measurements（2～300 K） agree with a weak antiferronmagnetic interaction between neighboring Ni ions in the chain.

Magnetic properties and magnetocaloric effects in Tb6Co1.67Si3 compound

Magnetic properties and magnetocaloric effects of Tb6Coi.67Si3 have been investigated by magnetization measurement. This compound is of a hexagonal Ce6Ni2Si3-type structure with a saturation magnetization of 187emu/g at 5 K and a reversible second-order magnetic transition at Curie temperature TC = 186K. A magnetic entropy change △S = 7J·kg^-1·K^-1 is observed for a magnetic field change from 0 to 5T. A large value of refrigerant capacity （RC） is found to be 330 J/kg for fields ranging from 0 to ST. The large RC, the reversible magnetization around Tc and the easy fabrication make the Tb6Co1.67Si3 compound a suitable candidate for magnetic refrigerants in a corresponding temperature range.

Nitrogen-Induced Change of Magnetic Properties in Antiperovskite-Type Carbide:Mn3InC

The effects of N substitution on the magnetic properties of Mn3InC1-xNx （0.0≤ x ≤0.7） are investigated sys- tematically. Partial substitution of N for C leads to the monotonic reduction in both the Curie temperature Tc and saturated magnetization Ms. The final results obtained from thermo-magnetie curves demonstrate that Mn3InC1-xNx samples show a magnetic phase transition from a paramagnetic （PM） state to a ferrimagnetic （FIM） state consisting of ferromagnetic （FM） and antiferromagnetie （AFM） components. In addition, there is a competition between the AFM component and the FM component in the FIM state with the change of the N-doped content. Magnetic measurements of Mn3InC at 100 Oe and 5000 Oe indicate the metastability and the coexistence of different magnetic phases at lower temperature. The spans of FIM phase broaden gradually with further N doping. The mechanism for the induction of the complicated magnetic state is still in controversy. However, the results clearly show that the doping at the X site in antiperovskite Mn3AX materials is as useful as that of the A and Mn sites.