Magnetocrystalline anisotropy of Ni and Mn substituted Nd2Fe14B compounds

Measurements of the effects of Ni and Mn substitutions for Fe on the magnetic properties of Nd₂Fe₁₄B compounds are reported. The Curie temperature is slightly increased with Ni substitution whilst in the case of replacement of Fe by Mn it is reduced drastically. A monotonic decrease of both the lattice parameters a and c is observed. The saturation magnetization is decreased by both Ni and especially Mn substitutions. The composition dependence of both the reorientation spin transition temperature and the cone angle has been measured. The influence of the 3d metal substitution on the Nd anisotropy has been measured and discussed. The composition dependence of the room temperature anisotropy field values, which is an important figure of merit for permanent magnet applications, decreases slightly in the case of Ni and drastically for Mn substitution. A comparison with the case of Co substitution has been made.     

Magnetocrystalline anisotropy of magnetite

The spin reorientation temperature T(SR) of stoichiometric Fe(3)O(4), as well as of magnetite with a small number of vacancies and magnetite containing a low concentration of Ti, Zn, Al and Ga was measured on single-crystal samples using the ac susceptibility. In the same experiment the temperature T(V) of the Verwey transition was also found. The results show that a correlation between T(SR) and T(V) exists. The electronic structure of the compounds studied was determined using the density-functional-based GGA + U method. For stoichiometric magnetite the first and second cubic anisotropy constants were calculated, while for magnetite with defects the distribution of electron density using the 'atoms in molecules' approach was determined. Based on a combination of experimental results with the electronic structure calculations an explanation of the temperature dependence of the magnetocrystalline anisotropy of magnetite is suggested.     

Research on the origin of magneto-crystalline anisotropy in R2Fe14B compounds

A model for the calculation of the magneto-crystalline anisotropy in R₂Fe₁₄B (R is a rare earth) compounds is presented. According to the model, a combined effect on the R-ion, coming from both the crystal field of ligands and the electric field of itinerant electrons, results in the anisotropy of the compounds. An approach of calculating the interaction between the itinerant electrons and the central R-ion is given. Taking account of the combined effect, we calculated the temperature dependences of the anisotropy of all the five R₂Fe₁₄B-type (R = Pr, Nd, Tb, Dy and Ho) compounds with uniaxial anisotropy. The results are in good agreement with the experiments. The calculation has shown that the effect of the itinerant electrons plays an important role for the anisotropy of the compounds.     

Magnetocrystalline anisotropy in permalloy revisited

Permalloy with a body-centered-cubic structure has been grown on GaAs(001) by molecular beam epitaxy. Its magnetism, Curie temperature, and magnetic anisotropy are determined experimentally and compared to those of conventional face-centered-cubic Permalloy. Unexpectedly the vanishing magnetic cubic anisotropy in Permalloy is found to be independent of its atomic structure but depends only upon the stoichiometry of Fe and Ni in the FexNi1-x alloy. This observation is further investigated and confirmed by first-principles electronic band calculations, which help to understand the long-standing issue of why Permalloy should be a soft magnet.     

Magnetocrystalline anisotropy of neutron small-angle scattering from an FeNi invar alloy

Small-angle scattering of neutrons from an Fe₆₅Ni₃₅ single crystal with an applied magnetic field parallel to each of 〈100〉, 〈110〉 or 〈111〉 has shown evidence for magnetocrystalline anisotropy.     

Positive muon spectroscopy of Nd2Fe14B and Pr2Fe14B

We have performed positive muon spin rotation measurements on polycrystalline samples of Nd₂Fe₁₄B and Pr₂Fe₁₄B in zero applied field. In both samples a single sharp μSR line was observed which was unexpected in this complicated structure. The temperature dependence of the muon frequency for Nd₂Fe₁₄B clearly reflects the spin reorientation below 150 K and can be explained qualitatively by assuming that only the c-axis component of a magnetization is sampled by the muon. A smooth decrease of the muon frequency with increasing temperature is observed for Pr₂Fe₁₄B.     

Magnetocrystalline anisotropy in FeNi invar alloys under high magnetic fields

Torque measurements were made for FeNi Invar alloys at 4.2 K in high magnetic fields up to 47 kOe by using a split pair type superconducting magnet. It was found that the magnetocrystalline anisotropy constant, K₁, determined from the observed torque curves increases monotonically with increasing the field. The increasing rate, $\text{d}\text{K}{}_1\text{d}\text{H}$, was extraordinally high and could not be explained by simply considering the Zener's power law. It was suggested that some other terms, such as the Fermi-level dependent one, play an important role in this quantity.     

Atomic origin of magnetocrystalline anisotropy in Nd(2)Fe(14)B

The magnetic moment reversal at each of the two inequivalent Nd sites in a single crystal of ferromagnetic Nd(2)Fe(14)B is probed by dichroic resonant diffraction of circularly polarized x rays. The results, supported by theory, show that the c-axis intrinsic magnetic stability of this superior permanent magnetic material arises predominantly at one of the Nd sites (g). The other site (f) undermines magnetic stability by favoring a magnetic moment orientation in the basal plane.     

Magnetocrystalline anisotropy and inversion degree of manganese-ferrous-ferrites

Torque measurements have been performed at 4 and 77 K on single crystals of Mn_1?xFe_2+xO₄ (0<x<0.05) and MnFe_2?xTi_xO₄ (0<x<0.1). The crystals were either quenched or slowly cooled causing a change of inversion by 0.1. It is found that the magnetic anisotropy due to the ferrous ions in the Ti-doped samples is 80 per cent larger than in the Mn_1?xFe_2+xO₄ crystals. In both crystal series the ferrous ion anisotropy in the slowly cooled crystals is 70 per cent higher than in the quenched crystals. The K₁ of MnFe₂O₄ at 4 K is found to decrease from ?3.6 × 10⁵ erg/cm³ after show cooling, down to ?2.6 × 10⁵ erg/cm³ after quenching.     

取向Pr2Fe14B与Nd2Fe14B多晶磁化曲线的计算

基于单离子晶场模型 ,提出了计算稀土 Fe(Co)金属间化合物取向多晶样品磁化曲线的方法 .用此方法计算了取向Pr2 Fe14 B和Nd2 Fe14 B多晶的高场磁化曲线 ,计算中使用了拟合化合物单晶磁化曲线得到的交换场与晶场参数 .计算曲线与实验曲线相符合 .     

Magnetocrystalline anisotropy of MnF2 deduced from static torque

The first anisotropy constant K₁ as well as the differential susceptibility ΔX = Xχ - X∥ of MnF₂ has been determined from static torque measurements. The temperature range was for K₁ 4.2 K to 66 K and for ΔX 4.2 K to 300 K. The result for K₁ is in good agreement with values obtained from antiferromagnetic resonance experiments. In order to explain the differential susceptibility in the paramagnetic region, it was found necessary to take the g-factor anisotropy into account.     

Kerr effect in R2Fe14B and R2Co14B compounds

The polar Kerr effect in several compounds of the R₂Fe₁₄B and R₂Co₁₄B series (R=rare earth metal) at room temperature was measured in the energy range 0.5–5 eV. It was found that the 3d sublattice magnetization is mainly responsible for the Kerr effect. The potential use of R₂Fe₁₄B compounds for erasable magneto-optical recording is briefly discussed.     

钕铁硼的冲击压缩特性

 利用二级轻气炮对恒磁体钕铁硼进行冲击压缩,采用阻抗匹配法进行测量,获得了平均初始密度为7.346 g/cm³的钕铁硼Hugoniot关系数据。实验结果表明,该种钕铁硼在19~78 GPa范围内,其D-u_p满足线性变化关系,即：C₀、λ分别为3.686 km/s、1.059,是一种稳定的压缩过程,其间没有相变产生。而较小的λ值表明该种钕铁硼材料偏向于疏松体结构,且容易被压缩。同时实验结果也为其状态方程和脉冲功率源等方面的研究工作提供了可资参考的实验参数。     

A note on exchange and crystal field interactions in R2Fe14B compounds: Yb2Fe14B

The R₂Fe₁₄B phase has been found to exist for R=Yb. The magnetic properties presented in this paper complete the characterization of the compounds in this series for which the Stevens α_J coefficient of the R³⁺ ion is positive. ⁵⁷Fe Mössbauer spectroscopy establishes the existence of a magnetization reorientation at 115 K of the type observed in Er and Tm compounds associated with a small Fe magnetization anisotropy. From the neutron diffraction measurements obtained at 4.2 K with and without an applied magnetic field, the easy direction of magnetization was found to be along the [100] direction, in the basal plane of the tetragonal structure. These results show that in all compounds where α_J>0 for the R³⁺ ion, the easy direction of magnetization in the plane is determined by the second order crystal field terms and rare earth-Fe exchange interactions and is independent of the sign of the 4th order crystal field terms.     

Mössbauer study of Nd2Fe14B and Nd2(Fe1−xCox)14B compounds

The Mössbauer spectra of Nd₂Fe₁₄B and Nd₂(Fe_1?xCo_x)₁₄B compounds (x=0.0.05, 0.10 and 0.16) have been investigated at room temperature and at 77 K. Taking advantage of combined ME and NMR investigations of the Nd₂Fe₁₄B compund, the hyperfine field values and their assignment to the six Fe sites have been determined to be the following sequence: 378(j₂), 346(k₂), 334(j₁), 325(k₁), 322(c), 306(e) kOe. The substitution of Co for Fe decreases the hyperfine fields at all Fe sites. The intensity variations of the subspectra with Co content show that Co atoms have a strong preference to occupy the k₂ site, but have a rather less tendency to enter the j₂ site, which is preferred by Fe atoms.