Y3Fe5-xMnxO12的磁结构和磁性能

对多晶Y₃Fe₃Fe_5-xMn_xO₁₂(x=0.05和0.09),得到300K下的中子衍射曲线。发现当x=0.05时,Mn³⁺离子占据16a和24d位置的几率分别为0.72和0.28;当x=0.09时,Mn³⁺离子全部占据16a位置;还得到两种组分16a和24d位置各自的磁矩值。在外磁场(800—10KOe)下测量Y₃Fe_5-xMn_xO₁₂(x=0—0.11)的磁化曲线,温度范围是1.5—300K。得到饱和磁矩值;并利用趋近饱和定律确定1.5K下的磁晶各向异性常数k₁值,发现|k₁|值随含锰量增加而减小。 关键词：     

First-principles study on the electronic structure and the ferromagnetic properties of the cyano-bridged bimetallic compound Mn2(H2O)5Mo(CN)7·4H2O (α phase)

First-principles calculations have been performed to study the electronic structure and the ferromagnetic properties of the cyano-bridged bimetallic compound Mn₂(H₂O)₅Mo(CN)₇·4H₂O (α phase).The calculations were based on density-functional theory and the full potential linearized augmented plane wave method (FP-LAPW). The calculated total energies revealed that the compound has a stable ferromagnetic (FM) ground state, which is in agreement with the experiments. The electronic structure of the compound has a half-metallic behavior. The calculated magnetic moment per molecule is about 15.000 μ_B, the magnetic moment are mainly from Mo and Mn atoms with d electronic configuration. It is also found that there exists ferromagnetic interaction between low-spin Mo²⁺ and high-spin Mn³⁺ ions through the Mo-C-N-Mn linear linkages.     

Magnetic characterization of Mn5SiB2 and Mn5Si3 phases

In this work the Mn₅Si₃ and Mn₅SiB₂ phases were produced via arc melting and heat treatment at 1000 °C for 50 h under argon. A detailed microstructure characterization indicated the formation of single-phase Mn₅Si₃ and near single-phase Mn₅SiB₂ microstructures. The magnetic behavior of the Mn₅Si₃ phase was investigated and the results are in agreement with previous data from the literature, which indicates the existence of two anti-ferromagnetic structures for temperatures below 98 K. The Mn₅SiB₂ phase shows a ferromagnetic behavior presenting a saturation magnetization M_s of about 5.35×10⁵ A/m (0.67 T) at room temperature and an estimated Curie temperature between 470 and 490 K. In addition, AC susceptibility data indicates no evidence of any other magnetic ordering in 4-300 K temperature range. The magnetization values are smaller than that calculated using the magnetic moment from previous literature NMR results. This result suggests a probable ferrimagnetic arrangement of the Mn moments.     

Electronic structure and magnetism in full-Heusler compound Mn2ZnGe

The first-principle calculations within density functional theory are used to investigate the electronic structure and magnetism of the Mn₂ZnGe Heusler alloy with CuHg₂Ti-type structure. The half-metallic ferrimagnets (HMFs) in Mn₂ZnGe are predicted. The energy gap lies in the minority-spin band for the Mn₂ZnGe alloy. The calculated total spin magnetic moment is −2μ_B per unit cell for Mn₂ZnGe alloy, the magnetic moments of Zn and Mn(B) are antiparallel to that of Mn(A), and we also found that the half-metallic properties of Mn₂ZnGe are insensitive to the dependence of lattice within the wide range of 5.69 and 5.80 Å where exhibiting perfect 100% spin polarization at the Fermi energy.     

Non-spherical magnetic moment in MnAlGe

The magnetic structure factors of MnAlGe (space groupP4/nmm) measured with polarised neutrons have been expressed in terms of the magnetic moment of the Mn atom (site symmetry tetrahedral with tetragonal distortion), the Bessel transforms 〈j _n〉 of the Mn radial functions and the fractional occupancies of the moment density in the various crystal field orbitals. The measured structure factors were least-squares fitted with the theoretical expression involving 〈j _n〉 appropriate to the Mn⁰, Mn⁺ and Mn²⁺ atoms. The best fit was got using Mn⁰ transforms, yielding 1·45µ _B as the Mn magnetic moment. The fractional occupancies of the moment density in the crystal field orbitalsA _1g,B _1g E _g andB _2g were obtained. This analysis shows the magnetic moment to be highly non-spherical with a large fractional occupancy (38%) in theA _1g orbital directed along the tetragonal axis while the fractional occupancies ofB _1g andB _2g are found to be 31% and 30% respectively. The fractional occupancy of the moment in theE _g orbital directed towards the Ge and Al atoms is very low (1%). The spatially averaged moment density of Mn in MnAlGe is more diffuse than that of Mn I and Mn II in isostructural Mn₂Sb.     

Structural,electronic, magnetic and thermoelectric properties of inverse Heusler alloys Ti2CoSi,Mn2CoAl and Cr2ZnSi by employing Ab initio calculations

ABSTRACT

The inverse Heusler alloys such as Ti₂CoSi, Mn₂CoAl and Cr₂ZnSi were studied in the framework of density functional theory using FP-LAPW linearised augmented plane wave method in order to determine the different physical properties such as structural, electronic, magnetic and thermoelectric. The generalised gradient approximation (GGA) was used to treat the exchange–correlation energy and the Beck-Johnson (mBJ) approach was used to calculate the electronic properties. In all studied compounds, the stable type Hg₂CuTi was energetically more favourable than Cu₂MnAl type structure. The results show that two compounds (Ti₂CoSi and Mn₂CoAl) are both ferromagnetic (FM) while Cr₂ZnSi is antiferromagnetic (AFM). The compounds Ti₂CoSi and Mn₂CoAl have a total magnetic moment of 3 and 2?μ_B, respectively, whereas the Cr₂ZnSi alloy has a total magnetic moment equals zero. The Ti₂CoSi, Mn₂CoAl and Cr₂ZnSi compounds exhibit half-metallic (HM) character with 100% spin polarisation at the Fermi level. Finally, the semi-classical Boltzmann theory implicit in the BoltzTraP code was used to calculate the electronic transport coefficients such as thermal and electrical conductivity, the Seebeck coefficient and the factor of merit.     

Magnetic and ferroelectric properties of exchange-frustrated multiferroics (Ni1 ? xTx)3V2O8 (T = Co, Mn, Zn)

The effect of the substitution of Co²⁺, Mn²⁺, and Zn²⁺ ions for Ni²⁺ ions on the magnetic, dielectric, and ferroelectric properties of vanadate single crystals (Ni_{1 − x} T _x )₃V₂O₈ has been analyzed. It has been found that the low-level (x ≤ 0.1) substitution of both magnetic and nonmagnetic ions stabilizes the ferroelectric state with a cycloidal magnetic structure. The existence region of this state is expanded to low temperatures down to 3 K for Zn²⁺ and below 1.8 K for Co²⁺ and Mn²⁺ owing to the suppression of a low-temperature weak ferromagnetic phase. At the same time, the ferroelectric phase disappears completely at large concentrations of Co and Mn. The effect of magnetic fields on the magnetic and ferroelectric states has been analyzed. It has been shown that the magnetic field along the c axis suppresses the ferroelectric state, whereas the magnetization along the antiferromagnetism axis (a axis) induces the reentrant phase transition from a paraelectric weak ferromagnetic structure to a ferroelectric structure. The corresponding H-T phase diagrams have been drawn.     

Spin-glass in the spinel-type CuCrTiS4

It is difficult to find a typical compound to understand the spin-glass (SG). Only a few model compounds for the SG have been investigated; Fe_0.50Mn_0.50TiO₃ as a short-range interacting three-dimensional (3D) Ising SG, Dy_0.103Y_0.897Ru₂Si₂ as a long-range 3D Ising SG, and AgMn as a long-range 3D Heisenberg SG. A spinel-type compound CuCrTiS₄ will be provided in this study as a realistic candidate for a short-range interacting 3D Heisenberg SG. This CuCrTiS₄ can cause a SG phase below T _g?=?7.91?K, which is obtained by a random non-magnetic 50% substitution of Ti for Cr on B-sites in the ferromagnetic mother spinel CuCr₂S₄. The localized magnetic moment of CuCrTiS₄ comes from Cr³⁺ with S?=?3/2, where a valence state of Cu⁺Cr³⁺Ti⁴⁺S₄ ^2? is built up. Experimental data will be focused only on the static properties of dc magnetization M(T) under various magnetic fields, without any dynamical magnetic feature. The spin-glass phase transition T _g is well defined at low field, nevertheless hardly in higher fields than approximately 40 Oe. An appearance of the field dependence of M(T) of CuCrTiS₄ is similar to that of Fe_0.50Mn_0.50TiO₃ with the short-range Ising SG, and also these of AgMn and CuMn with the long-range interacting Heisenberg SGs. This general nature in M(T) seems to originate from the common mechanism under magnetic fields for all the spin-glasses.     

Effect of temperature conditions of ion implantation on percolation ferromagnetism in Ge0.98Mn0.02 thin films

The effect of temperature conditions of ion implantation on the magnetic properties of Ge_0.98Mn_0.02 thin films has been studied. It has been shown that a decrease in the implantation temperature significantly increases the temperature of percolation magnetic ordering in the subsystem of dispersed Mn²⁺ ions. It has been demonstrated that the observed effect can be due to suppression of the thermally activated aggregation of Mn²⁺ ions into Ge₃Mn₅ clusters and increase in their concentration in the dispersed state.     

Structures and magnetic behaviours of TiO2-Mn-TiO2 multilayers

The TiO2-Mn-TiO2 multilayers are successfully grown on glass and silicon substrates by alternately using radio frequency reactive magnetron sputtering and direct current magnetron sputtering. The structures and the magnetic behaviours of these films are characterised with x-ray diffraction, transmission electron microscope (TEM), vibrating sample magnetometer, and superconducting quantum interference device (SQUID). It is shown that the multi-film consists of a mixture of anatase and rutile TiO2 with an embedded Mn nano-film. It is found that there are two turning points from ferromagnetic phase to antiferromagnetic phase. One is at 42 K attributed to interface coupling between ferromagnetic Mn3O4 and antiferromagnetic Mn2O3, and the other is at 97 K owing to the interface coupling between ferromagnetic Mn and antiferromagnetic MnO. The samples are shown to have ferromagnetic behaviours at room temperature from hysteresis in the M-H loops, and their ferromagnetism is found to vary with the thickness of Mn nano-film. Moreover, the Mn nano-film has a critical thickness of about 18.5 nm, which makes the coercivity of the multi-film reach a maximum of about 3.965×10 2 T.     

Magnetic characterization of Bi2FeMnO6 film grown on (100) SrTiO3 substrate

Single phase Bi₂FeMnO₆ films on (100) SrTiO₃ substrate were fabricated using a pulsed laser deposition method through optimization of the preparation conditions. The magnetic moment is 0.30μ_B at 5 K in the magnetic field of 1 T, indicating that B site cations of Fe and Mn are disordered in the sample. The zero‐field‐cooling (ZFC) and field‐cooling (FC) magnetization curves measured from 2 K to 400 K coincide at 360 K. This is consistent with the observation that hysteresis disappears at 360 K, revealing the antiferromagnetic transition at this temperature. A spin‐glass‐like behaviour was observed at low temperature (～100 K) with a cusp of 25 K. Mn shows multiple valence states in the film. It is possibly because Mn²⁺ and Mn⁴⁺ could decrease the Jahn–Teller effect from Mn³⁺ in the film which results in less lattice distortion. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

NdNi2Ge2化合物的结构和电磁输运性质

利用非自耗真空电弧熔炼法制备了NdNi₂Ge₂化合物样品,采用X射线粉末衍射技术和Rietveld全谱拟合分析方法测定了其晶体结构. 结果显示该化合物的空间群为I4/mmm,点阵参数为:a=4.120(1),c=9.835(0),Z=2,Nd原子占据2a晶位,Ni原子占据4d晶位,Ge原子占据4e晶位. NdNi₂Ge₂化合物呈现顺磁性,应用居里-外斯定律拟合计算得到居里-外斯常数为25.8,居里-外斯温度为6.24 K. 有效势磁矩为3.69μ_B,这与理论计算Nd³⁺的磁矩相符,表明磁矩主要源于Nd³⁺. 电阻率变化范围为0.3 Ω ·μm^-1-1 Ω ·μm,电阻曲线拟合显示NdNi₂Ge₂呈半金属性. 关键词： 2Ge₂')" href="#">NdNi₂Ge₂ Rietveld结构精修 电磁输运     

外磁场对(Ga，Mn)As有效g因子的影响

利用时间分辨Kerr旋光技术测量低温下稀磁半导体Ga_0.937Mn_0.063As中光注入极化载流子的自旋进动信号,并观察到自旋极化载流子的有效g因子值随外磁场的增强而增大的反常现象.这归结于磁场导致局域化空穴转化为非局域化空穴,从而使自发磁化强度增强,有效g因子值增大.基于此物理图像,进一步给出了(Ga,Mn)As的有效g因子与外磁场的关系式. 关键词： 时间分辨Kerr旋光测量 Zeeman效应 Ruderman-Kittel-Kasuya-Yosida模型     

Crystallographic and magnetic phase transition in TlMnCl3

The results of our NMR, EPR and magnetic susceptibility measurements in the paramagnetic state of TlMnCl₃ are reported here. The NMR paramagnetic shift of thallium is found to be small but positive. Mn²⁺ EPR line is exchange narrowed. The susceptibility measurements indicate an antiferromagnetic transition. The heat of crystallographic phase transition ΔH, in TlMnCl₃ has been measured using differential scanning calorimetry. The crystallographic phase transition appears to be first order and ΔH is unusually low viz. 10 cal mole⁻¹. In the case of KMnF₃ Δ_H, which is reported here for the first time, is determined to be 2 cal mole⁻¹.     

Volume dependence of electronic structure and magnetic properties of Fe16N2

Using first-principles calculations based on density functional theory, we investigated systematically the electronic structures and magnetic properties of Fe₁₆N₂ system and their unit cell volume dependence. It has been found that total magnetic moment increases as increasing unit cell volume of Fe₁₆N₂. In addition, it also has been found that the d electron number on Fe I, Fe II and Fe III atoms decreases as increasing unit cell volume and the local magnetic moment on Fe atoms increases with the decrease of d electron number. The present study provides a clear insight into the numerous conflicting experimental results on the magnetic properties of Fe₁₆N₂ system.     

KKR-CPA-LDA计算方法对CuMnAl和CoMnAl以及CuCoMnAl合金的磁性研究

采用KKR-CPA-LDA方法研究了CuMnAl,CoMnAl和CuCoMnAl四元合金中磁性原子磁矩和Co-Mn间的交换作用.通过与实验结果对比,揭示了Mn的磁矩和Co的磁矩以及它们的相互作用随成分变化的规律.研究发现,在Cu₅₀Mn_25+xAl25-x合金中超过化学配比并占据Al位的Mn原子是反铁磁的,而且由于近邻环境的不同,其磁矩大于原有Mn原子的磁矩.在Co₅₀Mn_{25+< 关键词： KKR-CPA-LDA计算 Co-Mn间交换作用}     

First-principles study of the effect of iron doping on the electronic and magnetic properties of TbMn2O5

We have studied the electronic and magnetic properties of TbFe_xMn_2−xO₅ (x=0, 0.125, 0.25) samples using first-principles density functional theory within the generalized gradient approximation (GGA) schemes. The crystal structure of TbMn₂O₅ is orthorhombic containing Mn⁴⁺O₆ octahedra and Mn³⁺O₅ pyramids. The structure changes to monoclinic symmetry for the Fe-doping at the Mn sites. Our spin-polarized calculations give an insulating ground state for TbMn₂O₅ and a metallic ground state for Fe-doped TbMn₂O₅. Based on the magnetic properties calculations, it is found that the magnetic moment enhances with increase in the Fe-content in TbMn₂O₅. Most interestingly, the enhanced magnetic moment is due to a substantial reduction of the magnetic moments at the Fe sites.     

Field induced magnetic density in the Pauli paramagnet YNi5

The induced magnetic density of the enhanced Pauli paramagnet YNi₅ has been measured by polarized neutron diffraction at 100 K and in an applied field of 48 kOe. The magnetic density is localized on Ni sites where a 3d form factor, similar to that of Ni metal, is observed. The induced Ni moment is different for the two crystallographic sites: (2.4 ± 0.6) × 10^-3 μ_B on Ni_I on the 2c site and (4.1 ± 0.8) × 10^-3 μ_B on Ni_II on the 3g site. This difference must be associated with the difference of the Y surroundings of each site. The results are discussed from the band structure of the alloy.     

Mn site substitution of La0.67Ca0.33MnO3 with closed shell ions: Effect on magnetic transition temperature

Mn site is substituted with closed shell ions (Al, Ga, Ti, Zr and a certain combination of Zr and Al) and also with Fe and Ru ions carrying the magnetic moment (S=5/2 and 2 respectively) at a fixed concentration of 5 at %. Substitution did not change either the crystal symmetry or the oxygen stoichiometry. All substituents were found to suppress both the metal-insulator and ferromagnetic transition temperatures (T _p(ρ) and T _C, respectively) to varied extents. Two main contributions identified for the suppression are the lattice disorder arising due to difference in the ionic radii between the substituent (r _M) and the Mn³⁺ ion (r _Mn ³⁺) and in the case of the substituents carrying a magnetic moment, the type of magnetic coupling between the substituent and that of the neighboring Mn ion.     

四元Heusler合金NiMnFeGa中Fe原子的磁性贡献

用熔炼和甩带的方法制备了组分为Ni₅₀Fe_xMn_25-xGa ₂₅(x=0—25) 的系列样品.x射线衍射实验结果表明，当Fe取代Mn的含量x＜17时，用熔炼和甩带的方法均 能合成高度有序的L2₁结构的Heusler相.而当x＞17时，普通熔炼方法只能得到 低有序度的 γ相，只有采用甩带急冷的方法才能获得高度有序的纯L2₁结构的化合物.根据 交流磁化率 和分子磁矩的测试结果，初步分析了Fe原子对化合物磁性的贡献，认为Fe原子占据了Mn原子 的位置后，具有高于一般含铁合金的原子磁矩，可达2.55—3.55μ_B. 关键词： Heusler合金 50Fe_xMn_25-xGa_{25')" href="#">Ni50FexMn25-xGa25}