Temperature variation of the spin reorientation in Er2−xDyxFe14B alloys

The competition between the uniaxial magnetic anisotropy of the iron sublattice and the basal anisotropy of the rare earth sublattice in the R₂Fe₁₄B alloys, occuring for the rare earths with a positive Steven's factor (a_j> 0), leads to spin reorientation at 316 K for the Er₂Fe₁₄B compound. We have succeeded, by making a series of pseudoternaries of the type Er_2−xDy_xFe₁₄b, to establish a correlation between the spin reorientation temperature and the quantity x. Mossbauer spectra of aligned powders show a smooth decrease of the spin reorientation temperature for values of x up to 1, while for larger values spin reorientation is absent.     

Mössbauer spectroscopy on RE2Fe14BHx (RE-Y,Ce, Dy,Er) alloys

RE₂Fe₁₄B alloys and some of their hydrides have been studied through⁵⁷Fe and¹⁶¹Dy Mössbauer spectroscopy (MS). For both the paramagnetic and ordered phases a consistent and physically sound analysis of the⁵⁷Fe spectra is presented. Fe hyperfine fields and the local magnetic moments are obtained and compared with magnetic and structural data. A spin reorientation is observed for Er₂Fe₁₄B. A constant collinear structure down to 4.2 K was determined for the other samples. The¹⁶¹Dy spectra are interpreted for a pure ¦J_Z=15/2 > ground multiplet in Dy₂Fe₁₄B and its hydride. The B₂ crystal field parameters were estimated empirically for the Dy-alloy. Their values can account for the anisotropy in the compounds.     

Spin reorientation and magnetization anomaly in Er2Fe14B and Tm2Fe14B

Static magnetic measurements have been carried out on single crystals of Er₂Fe₁₄B and Tm₂Fe₁₄B in a temperature range between 77 and 590 K. Spin reorientation phenomena have been found in both compounds slightly above room temperature. In Er₂Fe₁₄B, the easy direction of magnetization changes from [100] to [001] at 316 K as temperature increases, and Tm₂Fe₁₄B from [100] to [001] at 310 K. Anomalously large anisotropy in the saturation magnetization has been detected around the spin reorientation temperature.     

R2Fe14B(R=Ce,Pr,Gd)磁晶各向异性常数K1,K2随温度的变化

本文在1.5—300K温度范围内测量了R₂Fe₁₄B(R=Ce,Pr,Gd)各向异性常数K₁,K₂和各向异性场H_A随温度的变化。同时用单离子模型计算了Pr³⁺离子对Pr₂Fe₁₄B磁晶各向异性的贡献,得到与实验值半定量符合的结果。 关键词：     

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.     

Magnetic properties of Y2Fe14B and Nd2Fe14B single crystals

Y₂Fe₁₄B and Nd₂Fe₁₄B are ferromagnets in which 3d interactions are dominant. In Y₂Fe₁₄B, the

-axis of the quadraticque est de magnetization. The 3d anisotropy is an order of magnitude weaker than in YCo₅. In agreement with point-charge model, CEF potential in Nd₂Fe₁₄B favours the

-axis at 300 K. At low temperature, the magnetization reorientation observed results from competition between exchange and anisotropy.     

Positive muon spectroscopy of R2Fe14B

Muon spin rotation (μSR) experiments were performed on polycrystalline samples of R₂Fe₁₄B in zero applied field. In all samples a single spin precession frequency was observed. In Nd₂Fe₁₄B and Ho₂Fe₁₄B pronounced anomalies showed up in the temperature dependence of the μSR frequencies at the spin reorientation temperatures of 150 K and 60 K, respectively. Our data can be explained with the assumption that only thec-axis component of the magnetization is sampled by the muon. We find a strong dependence of the local field on the magnetic moment of the rare earth ion. This is in accordance with calculations of the dipolar fields at the assumed muon stopping site.     

Magnetic properties of rare earth-transition metal compounds

A survey is given of results obtained by means of rare earth and⁵⁷Fe Mössbauer spectroscopy on intermetallic compounds of rare earths (R) and 3d metals (M). It is shown how these results can be used to obtain experimental information on crystal field effects, magnetic anisotropy, magnetic moments and magnetic coupling constants. The types of compounds considered in this review comprise RM₅, R₂M₁₇, R₂Fe₁₄B, R₂Fe₁₄C, R₂Fe₁₇C _x and RFe₁₀V₂. The results obtained by Mössbauer spectroscopy are compared with other techniques and the discussion of relevant theoretical models is included.     

The dependence of coercivity on anisotropy field in sintered R-Fe-B permanent magnets

To investigate the dependence of intrinsic coercivity of R-Fe-B permanent magnets (R = rare earths) on the anistropy field of R₂Fe₁₄B, the temperature dependence of the intrinsic coercivity of Pr₁₅Fe₇₇B₈ and Nd₁₅Fe₇₇B₈ have been measured from 4.2 K to the Curie temperature of the magnets. Study of the interrelation between coercivity and anisotropy field by modifying the anisotropy field through atomic replacement in the rare earth sublattice has been also attempted in pseudobinary alloys (Nd_1−xR′_x)₁₅Fe₇₇B₈ with R′ = Tb, Dy and Er. A coercivity versus anisotropy field and composition. The R₁₅Fe₇₇B₈ has been constructed from the observed dependence of the coercivity on both temperature and composition. The role of boundary phases is discussed by comparing R₁₅Fe₇₇B₈ with SmCo₅ magnets.     

Some features of magnetic domain structure reorganization during spin-reorientation phase transitions of the first and second order

On the basis of magnetic domain structure investigations in single crystals of R ₂Fe₁₄B, RFe₁₁Ti, RCo₅ intermetallic compounds (where R is a rare earth metal) in the temperature region 4.2–400 K, the features of domain structure transformation during spin reorientation transitions of the first and second order are analyzed.     

166Er Mössbauer spectroscopy in the Er2Fe14B H¢L alloys

¹⁶⁶Er Mössbauer spectroscopy is investigated in Er₂Fe₁₄B and its hydride. The hyperfine interaction parameters are discussed and compared to those reported for other intermetallic Er alloys. A consistent interpretation of the hyperfine data along the RE₂Fe₁₄B series (RE = rare earth element) is proposed.     

Spin reorientations in R2Fe14-xCoxB systems (R = Pr,Nd and Er)

The effect of cobalt substitution on spin reorientation phenomena in R₂Fe_14-xCo_xB systems (R = Pr, Nd, Er) was studied by means of bulk magnetometry in the temperature range 4.2–1100 K. It was established that in the Nd-based system the introduction of cobalt resulted not only in a shift of the low temperature spin reorientation (cone to axis) but also triggered, for x ⩾ 10, an appearance of a second spin reorientation (axis to plane) at high temperature. In the Pr-based system, for x ⩾ 9.5, a high temperature spin reorientation (axis to plane) was also observed. Its dependence on Co content was determined. For the Er-based system, an increase of the spin reorientation temperature (plane to axis) was observed as more cobalt was introduced into that system. It was also established that the tetragonal single-phase materials in this system exist only up to x = 5. Temperature-composition diagrams are presented, indicating types of spin arrangements observed in the investigated systems.     

YTi(Fe1-xNix)11的晶体结构和内禀磁性

当x<0.7时,YTi(Fe_1-xNi_x)₁₁可形成单相的ThMn₁₂型四方结构,空间群14/mmm。本文研究了以Ni原子代换Fe原子时,对饱和磁矩、磁晶各向异性和居里温度的影响。通过代换研究,并讨论了Fe原子和Ni原子在稀土化合物中所表现的两种不同的特性。稀土-铁(R-Fe)金属间化合物的磁性依赖于Fe-Fe近邻原子的间距和数目;而R-Ni金属间化合物的磁性取决于稀土金属传导电子对Ni的3d能带的影响。为进一步确证这 关键词：     

Mössbauer study of the intermetallic compound Nd2Fe14B. I. interpretation of complex spectrum

The ⁵⁷Fe Mössbauer spectrum of the Nd₂Fe₁₄B compound at room temperature has been analyzed with a set of six subspectra due to six crystallographically non-equivalent sites of Fe-atoms. It was shown that there are three possible sets of six subspectra, and the most suitable one could be selected by considering how the hyperfine field and the isomer shift are influenced by near neighbor atoms. The result is applicable to the analyses of the spectra of Nd₂Fe₁₄B and Ho₂Fe₁₄B at room temperature. The order in magnitude of the hyperfine fields and that of the isomer shifts at the six Fe-sites is much the same for the three compounds, while the quadrupole splittings depend complicatedly on the kind of rare earth atom and/or on the lattice parameters.     

Properties of amorphous CoZr(RE) (RE=Gd,Sm, Dy) films with various uniaxial anisotropies,prepared by a new process

If a DC magnetic field is applied parallel to the plane of amorphous CoZr(RE) thin films during sputter depositing, a uniaxial anisotropy is formed the direction of which depends upon the choice of RE substituted and its concentration. When RE=Gd a perpendicular anisotropy K_p forms over a large concentration range, a spin reorientation process being at the origin of the process. A well-defined K_p is developed also in CoFeZrGd and CoZrGdSm films. CoZrGdDy films exhibit simultaneously a perpendicular and an in-plane uniaxial anisotropy. The related magnetization process and domain structures are quite peculiar.     

Influence of co-doping different rare earth ions on CaGa2S4: Eu, RE(RE=Ln) phosphors

Photoluminescent phosphors CaGa₂S₄: Eu²⁺, RE³⁺ (RE³⁺ including all rare earth ions except for Sc³⁺, Pm³⁺, Eu³⁺ and Lu³⁺) were prepared by sintering at high temperature in a reductive atmosphere, and their luminescent properties were studied intensively. The influences of co-doping rare earth ions on their luminescent properties were also investigated. No remarkable differences were found from excitation spectra of co-doped phosphors CaGa₂S₄: Eu²⁺, RE³⁺ in contrast with that of phosphor CaGa₂S₄: Eu²⁺, but there were a few differences in emission spectra of Ce³⁺, Pr³⁺ or Ho³⁺ co-doped phosphors. Phosphors CaGa₂S₄: Eu²⁺, RE³⁺ (RE=Ce, Pr, Gd, Tb, Ho and Y) had persistent afterglow, and very short afterglow was shown for Nd³⁺ or Er³⁺ co-doped phosphors, but no long afterglow appeared when auxiliary activator was La³⁺, Sm³⁺, Dy³⁺, Tm³⁺ or Yb³⁺. Among the phosphors with long-lasting phosphorescence, in our experiments, CaGa₂S₄: Eu²⁺, Ho³⁺ had the longest and the highest brightness long yellow afterglow. Thermo-luminescence of all co-doped phosphors was measured to find the answer of different influences from different rare earth auxiliary activators.     

Mössbauer spectroscopy of R2Fe14B and related compounds

The Mössbauer Spectroscopy (MBS) has been widely used in the last 4 years for the study of the recently discovered ternary compounds R₂Fe₁₄B where R means Y, Th or a rare earth element. The strong interest for this class of intermetallics arose drastically after the discovery of the exceptional properties of Nd₂Fe₁₄ as an ideal material for permanent magnet applications. The newest results about hyperfine fields B_HF, quadrupole splitting E_Q and isomer shifts I.S. at the 6 crystallographically different Fe sites and at the 2 R sites in the R₂Fe₁₄B and their impact on the understanding of the local magnetic moments and magnetocrystalline anisotropy will be reviewed. In the case of RFe_12?xM_x compounds where M=V, Ti, Si, Mo, W, Cr, complex Mössbauer spectra were obtained because of the presence of 3 crystallographically inequivalent Fe sites and the presence of differents amounts of the M component on one or more of these sites.     

An57Fe Mössbauer study of rare-earth intermetallic compounds R(Fe11Ti)

⁵⁷Fe Mössbauer spectra are reported for the ThMn₁₂ structure series of intermetallic compounds R(Fe₁₁Ti) (R=Y, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu). The Mössbauer spectroscopy of oriented absorbers has been used to study the spin reorientation transitions exhibited by the members of the series where the second-order Stevens coefficient α_J of the rare-earth (Nd, Tb and Dy) is negative. A simple model has been established to deduce the canting angle from the Mössbauer spectra of oriented absorbers. The results are analyzed in terms of a crystal-field model. The crystal field parameters must be increased significantly to account for the observed large anisotropy in the Sm(Fe₁₁Ti) compound, which may find applications as a permanent magnet.     

Electronic and high pressure elastic properties of RECd and REHg (RE=Sc,La and Yb) intermetallic compounds

Structural, electronic, elastic and mechanical properties of Cd and Hg based rare earth intermetallics (RECd and REHg; RE=Sc, La and Yb) have been investigated using the full-potential linearized augmented plane-wave (FP-LAPW) method within the density-functional theory (DFT). The ground state properties such as lattice constant (a₀), bulk modulus (B) and its pressure derivative (B′) have been obtained using optimization method and are found in good agreement with the available experimental results. The calculated enthalpy of formation shows that LaHg has the strongest alloying ability and structural stability. The electronic band structures and density of states reveal the metallic character of these compounds. The structural stability mechanism is also explained through the electronic structures of these compounds. The chemical bonding between rare earth atoms and Cd, Hg is interpreted by the charge density plots along (1 1 0) direction. The elastic constants are predicted from which all the related mechanical properties like Poisson’s ratio (σ), Young’s modulus (E), shear modulus (G_H) and anisotropy factor (A) are calculated. The ductility/brittleness of these intermetallics is predicted. Chen’s method has been used to predict the Vicker’s hardness of RECd and REHg compounds. The pressure variation of the elastic constants is also reported in their B₂ phase.     

Clarifying the basic phase structure and magnetic behavior of directly quenched (Ce,La)2Fe14B alloys with various Ce/La ratios

To improve the performance/cost ratio of NdFeB based permanent magnets, Ce or/and La substitutions for Nd have been suggested. To better understand the effects of these substitutions, the fundamental behavior of (Ce,La)-Fe-B alloys has to be clearly understood. Here, we reported a systematic investigation on the phase structure, microstructure, and magnetic properties of melt-spun (Ce,La)₂Fe₁₄B alloys. The results confirm that partial substitution of Ce by La can effectively enhance the hard magnetism and thermal stability of (Ce_1-xLa_x)₂Fe₁₄B alloys, while over 80% La substitution leads to the decomposition of 2:14:1 phase. The lattice parameters a, c and the Curie temperature T_c of 2:14:1 phase increase linearly with the increasing La content. La substitution can effectively refine the grain, resulting in the enhancement of inter-grain exchange coupling. The (Ce_0.7La_0.3)₂Fe₁₄B alloy with a mean grain size of 25 nm exhibits high remanence, maximum energy product and intrinsic coercivity up to 0.69 T, 6.2 MGOe and 217 kA/m, respectively. The present work provides a good understanding on the melt-spun (Ce,La)-Fe-B system for further developing low cost rare earth permanent magnets.