Rare-earth Transition-metal Compounds Research Articles

Synthesis, Structure, and Magnetic Properties of the Rare-Earth Zintl Compounds Eu14MnPn11 and Eu14InPn11 (Pn = Sb, Bi)

New rare-earth transition-metal compounds Eu14MnPn11 and Eu14InPn11 (Pn = Sb, Bi) have been prepared in quantitative yield from heating stoichiometric amounts of the elements, which are sealed in a welded tantalum tube that is enclosed in a fused silica ampule, at 950−1200 °C. These compounds are isostructural with the Zintl compound Ca14AlSb11 and crystallize in the tetragonal space group I41/acd (Z = 8). Single-crystal X-ray data (143 K) were refined for Eu14InSb11 (a = 17.280 (5) A, c = 23.129 (8) A, R1 = 4.04%, wR2 = 8.65%) and Eu14MnBi11 (a = 17.632 (4) A, c = 23.047(6) A, R1 = 4.53%, wR2 = 7.83%). The structures of these compounds are compared with Eu14MnSb11 and other compounds of this structure type. Magnetization measurements show that Eu14MnSb11 and Eu14MnBi11 order at approximately 100 and 35 K, respectively. The effective moment in the paramagnetic state for Eu14MnSb11 is μeff = 27.0(1) μB and for Eu14MnBi11 is μeff = 27.1(1) μB. Eu14MnSb11 saturates with μsat = 102 μB at 5 K whereas Eu14MnBi1...

Theory of X-Ray Absorption and Resonant X-Ray Emission Spectra

Resonant X-ray emission spectrum (RXES) has recently been a subject of remarkable progress. Theoretically, RXES is formulated as a coherent second order optical process, where the X-ray emission follows the X-ray absorption (XAS) of a core electron. In this paper I discuss from theoretical viewpoint XAS and RXES in f and d electron systems, which are calculated with an impurity Anderson model. Effects of intra-atomic multiplet coupling and interatomic hybridization are taken into account. RXES is calculated for some rare earth compounds and transition metal compounds as a function of the emitted photon energy ω, and it is shown that the RXES gives us information on the electronic excitations (multiplet states and charge transfer states) in the ground state configuration. When we regard RXES as a function of the incident photon energy it with fixed ω, the RXES gives us information on the core electron excited states (with more information than XAS). These results are also compared with available experimental data.

4f-3d interaction and magnetic anisotropy in ThMn12-type rare-earth transition-metal compounds

Rare-earth (R) transition-metal (T) compounds of the R(T,M)12-type with R=Y or one of the heavy-rare-earth elements, T=Fe or Co and M=Ti, V, Mo or Si, have been studied at 4.2 K in the Amsterdam High-Field Installation in magnetic fields up to 38 T and at temperatures between 4.2 and 1000 K in other magnetometers. The 4f-3d interaction is derived from magnetization measurements on single-crystalline particles that are free to rotate in the applied fields. The stabilizing element M is shown to have a pronounced influence on the 4f-3d interaction strength in these compounds. The large variation in Curie temperatures of the Y compounds and the different types of magnetic anisotropy found in the Y compounds demonstrate that the element M plays an important role in establishing these properties as well.

Mechanically alloyed hard magnetic materials

Recent developments in the synthesis of hard magnetic materials by mechanical alloying are reviewed. In rare earth-transition metal compounds the nanocrystalline structure developed by mechanical alloying and heat treatment results in ultra-high coercivity and isotropic behaviour associated with random grain alignment. Mechanically alloyed two phase exchange-coupled materials exhibit remanence enhancement, and the reversible and irreversible magnetisation behaviour of this novel class of permanent magnet is also discussed.

Synthesis in fine grain binary and ternary rare earth-transition metal compounds

Synthesis in fine grain binary and ternary rare earth-transition metal compounds

X-ray-absorption edge shifts in rare-earth-transition-metal compounds.

X-ray-absorption K-edge shifts of cobalt have been measured in ${\mathrm{Y}}_{2}$${\mathrm{Co}}_{17}$, ${\mathrm{YCo}}_{5}$, and ${\mathrm{YCo}}_{3}$ compounds whose crystal structures are derivatives of the ${\mathrm{CaCu}}_{5}$ structure. The edge shifts vary monotonically with the Y:Co ratio. We compare them with Fe, Y, and Ce edge shifts determined for several other related materials, including ${\mathrm{Y}}_{2}$${\mathrm{Fe}}_{17}$, ${\mathrm{Ce}}_{2}$${\mathrm{Fe}}_{17}$, and ${\mathrm{CeCo}}_{2}$. In all cases, the shifts are the same sign, a fact that points to the absence of a significant uncompensated charge transfer from one elemental constituent to another. Identifying the edge shifts as core-level shifts, we find that the Watson-Hudis-Perlman charge-compensation model is applicable to these systems; estimates of the model parameters lead to small net charge transfers consistent with available M\"ossbauer effect measurements. Our results show that there is no straightforward relation between the transition-metal magnetic moment and either charge transfer or corresponding absorption edge shift, which implies that the variation of the moment with stoichiometry in these materials is not governed by the filling of rigid transition-metal bands.

Effects of Ce vs. Lu substitution on the electronic structure of rare earth-transition metal compounds

We report the results of a combined UV photoemission and inverse photoemission spectroscopy investigation of some isostructural rare earth (R) intermetallic compounds, i.e. CeCo 2, LuCo 2, CeRh 2, LuRh 2, Ce 7Rh 3 and Lu 7Rh 3, aiming to highlight the effects, on both the occupied and unoccupied d-derived partial density of states, of R substitution on different transition metal (M) hosts. These effects cannot be detected by X-ray spectroscopies because of the sizeable f-related contribution while, for cross-section reasons, UV spectroscopies may allow direct access to the d-like states. The results are discussed in terms of the different spatial extents of Ce and Lu 5d wavefunctions and of the degree of intermixing with the M partner d valence states.

Cold compaction of iron powders by experiments and simulations : G. Coccoz et al (Ecole des Mines de Paris, Sophia Antipolis, France)

The revolutionary progress made in the field of permanent magnets over the past 25 years has been almost entirely due to a concentrated research effort in the field of rare earth-transition metal compounds. This paper discusses the unique intrinsic properties of such compounds as precursors for permanent magnets, and outlines possible coercivity mechanisms and their relationship with microstructure in the two main families of R-T permanent magnets: Sm-Co and Nd-Fe-B. The relationship between intrinsic and extrinsic properties is also briefly discussed.

Single-ion magnetic anisotropy of rare-earth-transition-metal compounds and its description by means of analytical expressions.

The single-ion magnetic anisotropy energy of 3d-4f compounds is shown to be generally irrepresentable in the form of analytical expressions involving anisotropy constants. Particular cases permitting analytical representation are analyzed and expressions for the anisotropy constants in terms of the crystal field and 3d-4f exchange parameters are derived. In particular, the high-temperature approximation appears useful for analysis of vital properties of hard magnetic materials. Limits of validity of the obtained formulas are established.

Micromagnetic theory of spin waves in rare-earth-transition-metal compounds.

The micromagnetic theory is a simple and powerful method to calculate the spin-wave dispersion relation in the long-wavelength region. The calculation has been performed within the framework of the two-sublattice model which is the adequate micromagnetic description for rare-earth--transition-metal compounds. A magnetocrystalline anisotropy of the easy-axis type is assumed and the cases of ferromagnetic and ferrimagnetic coupling of the two sublattices are considered. The theoretical results are compared to neutron-scattering data obtained from R${\mathrm{Fe}}_{2}$, ${\mathit{R}}_{2}$${\mathrm{Fe}}_{17}$, ${\mathit{R}}_{2}$${\mathrm{Co}}_{17}$, and ${\mathit{R}}_{2}$${\mathrm{Fe}}_{14}$B, with R representing different rare-earth atoms.

The free-powder magnetization of ferrimagnetic rare-earth transition-metal compounds — basal-plane anisotropy

The anisotropy in the basal plane is taken into account in the investigation of the magnetic exchange interaction between rare-earth (R) and transition-metal (T) sublattices of ferrimagnetic R-T intermetallic compounds. As a result of the non-zero basal-plane anisotropy, an oscillating magnetization curve is predicted.

Exchange interactions in rare earth—transition metal compounds

Using the strenght of R—R interactions deduced from the ordering temperatures of RNi 2 compounds, the R—T exchange-coupling parameter ( A RT) in R m T n ( R = rare earth, T = Co or Fe, m / n = 1 2 ; 1 3 ; 6 23 ; 1 5 ; 2 17 ; 1 12 ) and R mT nB k ( m / n / k = 1/4/1; 2/14/1; 1/12/6) systems has been evaluated from analyses of Curie temperatures. Whereas A RR , as deduced from the RNi 2 compounds, increases by almost an order of magnitude in a given series, A RT is enhanced by a factor of only about three from the heavy to the light rare earth compounds. These phenomena, already reported in literature, are based on 4f–5d exchange interactions at R sites. In addition, for a given rare earth element, going from T-poor to T-rich compounds, a tendency to decrease is found for both A RCo and A RFe; this variation is discussed in terms of 3d–5d hybridization.

Effects of the 3d—5d Hybridization on the 4f—3d Coupling in the Rare Earth—Transition Metal Compounds

Effects of the 3d—5d Hybridization on the 4f—3d Coupling in the Rare Earth—Transition Metal Compounds

Magnetism of nanostructured rare earth multilayers and films

A review is given of recent research on amorphous, compositionally modulated rare earth—transition metal films. Factors determining their magnetic structure, perpendicular magnetic anisotropy and magneto-optic properties are discussed. Thin films of rare earth—transition metal compounds which have strong permanent magnet properties are outlined. Many of the new complex compounds have been prepared as thin films with controlled anisotropies. Possible applications of such films are briefly discussed.

Ab initio calculation of the magnetism in GdFe 12

Electronic structure calculations by means of the LMTO-ASA method have been performed for the hypothetical rare earth-transition metal compound GdFe 12 with the ThMn 12 structure. The R-4f magnetic moments were obtained from the standard Russel-Saunders scheme but the radial 4f spin density was otherwise part of the self-consistent band calculation. The influence of localized 4f magnetism upon the conduction band magnetism is found to give noticeable changes in the local moments of the iron. The presence of the 4f spin moment is found to induce a redistribution of the conduction electron spin moment between the rare earth and iron sites while the total conduction moment remains practically constant.

Recent progress in the interpretation of nucleation fields of hard magnetic particles

In permanent magnets based on rare earth-transition metal compounds the value of the coercive field, H c, as well as the angular dependence of H c deviates considerably from the predictions of the conventional Stoner-Wohlfarth theory. This discrepancy in general is attributed to the role of microstructure in sintered and rapidly quenched magnets. In this paper we have studied the process of magnetization reversal in small parallelepipeds taking into account the effect of a strong inhomogeneous demagnetization field, H d, at the edges, and of oblique applied fields. On the basis of micromagnetism it is shown that the nucleation field; H N, is reduced considerably by the demagnetization field at edges and that the angular dependence of H C is less pronounced than in the case of ellipsoidal particles.

The magnetic behaviour of rare-earth—transition metal compounds

The basic exchange interactions will be discussed for a variety of (R, T) compounds, in particular RT 2 (R: rare earth, or Y; T: transition metal). A magnetic phase diagram for (R, Y)Co 2 compounds is derived. The combined effect of the volume and the molecular field caused by the rare-earth spins is demonstrated on R(Co, Fe) 2, (R, Y)Co 2, R(Co, Al) 2 and R(Co, Cu) 2, with an emphasis on the metamagnetic transition in the 3d-subsystem.

A rule for counting neighbours in rare-earth transition metal compounds

In (R, T) compounds (R: rare earth; T: 3d transition metal) such as R 2T 17, R 2T 14B, and so on, the exchange interaction between a rare-earth spin (operator) S R and the neighbouring 3d spins can be written as -2 J RT z RT S R·〈 S T〉, where 〈 S T〉 is a site average of the expectation value of the transition metal spins in the molecular field approximation. z RT is the number of nearest T neighbours of an R-atom. A more precise definition is given in the main text. Analogously, z TR, the average number of nearest R neighbours of a T atom can be defined. We stress that a consistent definition must lead to the relation z RT N R = z TR N T for a stoichiometric compound containing N R rare-earth atoms and N T transition metal atoms per formula unit. Appropriate definitions are discussed for more intricate cases, in particular for off-stoichiometric compounds.

Refinement of HfFe 6Ge 6 isostructural ScMn 6Sn 6 and TbMn 6Sn 6

ScMn 6Sn 6 and TbMn 6Sn 6 ternary stannides with HfFe 6Ge 6 type structure (S.G.:P6/mmm) have been studied by means of single crystal X-ray diffractometry. The anaylsis of the interatomic distances and crystal chemistry considerations allow the prediction of the possible occurrence of other isostructural rare-earth transition-metal compounds.

ChemInform Abstract: Intrinsic and Extrinsic Properties of Rare Earth‐Transition Metal Compounds and Permanent Magnets

Abstract The revolutionary progress made in the field of permanent magnets over the past 25 years has been almost entirely due to a concentrated research effort in the field of rare earth-transition metal compounds. This paper discusses the unique intrinsic properties of such compounds as precursors for permanent magnets, and outlines possible coercivity mechanisms and their relationship with microstructure in the two main families of R-T permanent magnets: Sm-Co and Nd-Fe-B. The relationship between intrinsic and extrinsic properties is also briefly discussed.