Rare-earth Transition-metal Intermetallics Research Articles

Targeted crystal growth of rare Earth intermetallics with synergistic magnetic and electrical properties: structural complexity to simplicity.

The single-crystal growth of extended solids is an active area of solid-state chemistry driven by the discovery of new physical phenomena. Although many solid-state compounds have been discovered over the last several decades, single-crystal growth of these materials in particular enables the determination of physical properties with respect to crystallographic orientation and the determination of properties without possible secondary inclusions. The synthesis and discovery of new classes of materials is necessary to drive the science forward, in particular materials properties such as superconductivity, magnetism, thermoelectrics, and magnetocalorics. Our research is focused on structural characterization and determination of physical properties of intermetallics, culminating in an understanding of the structure-property relationships of single-crystalline phases. We have prepared and studied compounds with layered motifs, three-dimensional magnetic compounds exhibiting anisotropic magnetic and transport behavior, and complex crystal structures leading to intrinsically low lattice thermal conductivity. In this Account, we present the structural characteristics and properties that are important for understanding the magnetic properties of rare earth transition metal intermetallics grown with group 13 and 14 metals. We present phases adopting the HoCoGa5 structure type and the homologous series. We also discuss the insertion of transition metals into the cuboctahedra of the AuCu3 structure type, leading to the synthetic strategy of selecting binaries to relate to ternary intermetallics adopting the Y4PdGa12 structure type. We provide examples of compounds adopting the ThMn12, NaZn13, SmZn11, CeCr2Al20, Ho6Mo4Al43, CeRu2Al10, and CeRu4Al16-x structure types grown with main-group-rich self-flux methods. We also discuss the phase stability of three related crystal structures containing atoms in similar chemical environments: ThMn12, CaCr2Al10, and YbFe2Al10. In addition to dimensionality and chemical environment, complexity is also important in materials design. From relatively common and well-studied intermetallic structure types, we present our motivation to work with complex stannides adopting the Dy117Co57Sn112 structure type for thermoelectric applications and describe a strategy for the design of new magnetic intermetallics with low lattice thermal conductivity. Our quest to grow single crystals of rare-earth-rich complex stannides possessing low lattice thermal conductivity led us to discover the new structure type Ln30Ru4+xSn31-y (Ln = Gd, Dy), thus allowing the correlation of primitive volumes with lattice thermal conductivities. We highlight the observation that Ln30Ru4+xSn31-y gives rise to highly anisotropic magnetic and transport behavior, which is unexpected, illustrating the need to measure properties on single crystals.

Diffusion Coefficients of Interest for the Simulation of Heat Treatment in Rare-Earth Transition Metal Magnets

In the case of the modeling of sintering and heat treatments, the diffusion coefficients are an essential input. However, experimental data in the literature about diffusion coefficients for rare-earth transition metal intermetallics is scarce. In this study, the available data concerning diffusion coefficients relevant for rare-earth transition metal magnets are reviewed and commented. Some empirical rules are discussed, for example the activation energy is affected by the size of the diffusing impurity atom. Diffusion coefficients for Dy, Nd and Fe into Nd2Fe14B are given according an Arrhenius equation D=D0exp (-Q/RT). For Dy diffusion into Nd2Fe14B, Q 315 kJ/mol and D08 . 10-4m2/s.

Magnetic anisotropy ofR2Fe14B(R=Nd, Gd, Y): Density functional calculation by using the linear combination of pseudo-atomic-orbital method

The magnetocrystalline anisotropy energy (MAE) of rare-earth transition-metal intermetallics ${R}_{2}{\text{Fe}}_{14}\text{B}$ ($R=\text{Nd}$, Gd, Y) was calculated by using the linear combination of pseudo-atomic-orbital method. Electronic structures were calculated by using relativistic density functional theory with Hubbard-type on-site Coulomb potential $U$ for $f$ electrons in the $R$ sites. The calculated magnetic moments of ${\text{Y}}_{2}{\text{Fe}}_{14}\text{B}$ and ${\text{Gd}}_{2}{\text{Fe}}_{14}\text{B}$ are in agreement with the experimentally measured saturation moments of these compounds. The calculated MAEs of ${\text{Y}}_{2}{\text{Fe}}_{14}\text{B}$ and ${\text{Gd}}_{2}{\text{Fe}}_{14}\text{B}$ are also in agreement with the value measured at low temperature. Moreover, it was found that the shape of the charge density at the Nd sites is aspherical, which causes larger MAE of ${\text{Nd}}_{2}{\text{Fe}}_{14}\text{B}$ than that of ${\text{Gd}}_{2}{\text{Fe}}_{14}\text{B}$. However, the orbital moment of the $4f$ electrons at the Nd sites and the MAE of ${\text{Nd}}_{2}{\text{Fe}}_{14}\text{B}$ were underestimated within the scope of a relativistic local-density approximation plus $U$ with spherical average potential.

Time-resolved studies of the order–disorder phase transformations in rare-earth–transition metal intermetallics with 2-17 stoichiometry

High-temperature order–disorder transformations in R2T17 and R2T17-M-C intermetallics with R = Pr, Sm, Dy, Tb; T = Co, Fe; and M = Zr, Nb were studied utilizing time-resolved synchrotron x-ray diffraction at the Advanced Photon Source (APS) at the U.S. Department of Energy’s Argonne National Laboratory (Argonne, IL). High-energy synchrotron radiation provides intense, highly penetrating x-rays, which are ideal for in situ studies of phase transformations. Alloying additions are used to stabilize formation of metastable phases; their influence on order recovery was investigated. The experimental setup utilized Debye–Scherrer geometry; specimens were heated at a rate of 10 K/min. Full-profile diffraction patterns collected every 10 s were refined in sequence using the Rietveld method to track changes of lattice parameters and phase assemblages during heating. Sharp changes observed in the evolution of temperature-dependent lattice parameters suggested formation of ordered structure via nucleation and growth. Both 2-17 polymorphs co-existed in light and heavy rare-earth systems at high temperatures. The presence of alloying additions in the solid solution greatly influenced long-range order formation.

Phase formation in rapidly solidified R2T17 intermetallics

Abstract Rapid solidification was utilized to produce a series of light and heavy rare earth-transition metal intermetallics in the R H –Co, R L –Co/Fe, and Sm–Co(Fe) systems with R H = Dy and Tb and R L = Pr and Sm. The influence of Nb–C and Zr–C additions on phase formation in the binary and ternary alloys has also been investigated. The X-ray diffraction patterns obtained with synchrotron radiation were refined by the Rietveld method for structural phase determination and analysis. It was found that the ability to create disorder strongly depended on the rare earth element, with light rare earth systems possessing more disorder, and rapid solidification effectively suppressed the development of long-range order in these compounds. Cobalt in contrast to iron favored the formation of disordered structures. Replacement up to two out of the three of the cobalt atoms with iron in the Sm–Co–Fe system has retained the establishment of the disordered TbCu 7 -variant and exhibited complete cobalt–iron solubility. Additions of Nb–C and Zr–C have also greatly influenced the order formation. The comparison of lattice parameters of the intermetallic compounds obtained by rapid solidification to the parameters of equilibrium 2–17 phases summarized in the literature revealed that formation of partially ordered and disordered structures was associated with expansion of the both a - and c -axes in Th 2 Zn 17 - and Th 2 Ni 17 -type phases for all binary compounds.

Finite-temperature anisotropy of magnetic alloys

The temperature dependence of the magnetic anisotropy of ferromagnetic materials is analyzed. Simple ferromagnets, such as Fe and Co, obey the m=n(n+1)∕2 power laws predicted by the Callen and Callen [Phys. Rev. 129, 578 (1963)] theory, but in alloys, the applicability of the theory is an exception rather than the rule. Many alloys, such as the rare-earth transition-metal intermetallics and L10 magnets, violate a basic assumption of the theory, namely, that the single-ion anisotropy and the spontaneous magnetization have the same origin. This is the reason for significant deviations from the Callen and Callen behavior, such as the m=2 law we obtained for L10 alloys.

From the electronic structure to the macroscopic magnetic behaviour of rare-earth intermetallics: a combination of ab initio electron theory with statistical mechanics and elasticity theory

It is shown that for a comprehensive theoretical understanding of magnetic anisotropy and magnetostriction of bulk and surface terminated single crystals and polycrystals of rare-earth metals and rare-earth–transition-metal intermetallics a combination of the ab initio density functional electron theory with statistical mechanics and stochastic elasticity theory is required. The crystal field parameters are calculated ab initio for the bulk and for the surface, and the possible temperature dependencies of the anisotropy constants are discussed. The components of the magnetostriction tensor are calculated for single crystals of Tb, Er and for TbFe 2, and for polycrystalline materials.

Synthesis of melt-spun rare-earth transition-metal intermetallics with Nd3(Fe,Ti)29-type structure

Rare-earth transition-metal intermetallics with the Nd 3 (Fe,Ti) 29 -type structure with R=Nd, Pr have been synthesized. The as-spun ribbons show a broad magnetic transition between 400 and 500 K. After annealing over a range of temperatures, 723–1373 K, and for times in the range 15–50 min, multiphase samples with the R 3 (Fe,Ti) 29 , R(Fe,Ti) 12 , R 2 (Fe,Ti) 17 and α-Fe phases are obtained. The optimum conditions are: for R=Nd the samples spun with a velocity of 30 m s −1 and annealed at 1373 K for 25 min contain Nd 3 (Fe,Ti) 29 as a main phase, 67 wt.%, with some Nd(Fe,Ti) 12 and α-Fe; for R=Pr the samples spun with a velocity of 20 m s −1 and annealed at 1323 K for 25 min contain 88 wt.% Pr 3 (Fe,Ti) 29 with some Pr 2 (Fe,Ti) 17 and α-Fe. These samples present Curie temperatures typical for the Nd 3 (Fe,Ti) 29 and Pr 3 (Fe,Ti) 29 compounds. The room-temperature saturation magnetization is 124.2 and 138.7 A m 2 kg −1 for R=Nd and 135.0 and 118.9 A m 2 kg −1 for R=Pr, before and after annealing, respectively. The annealed ribbons show grain sizes of <1 μm, and a mean stoichiometry of Nd 3 Fe 24 Ti 5 and Pr 3 Fe 26.5 Ti 2.5 for the 3:29 phase. The annealed samples present low coercivity values attributed to the presence of the soft α-Fe phase.

Finite-temperature behavior of anisotropic two-sublattice magnets

The finite-temperature magnetism of rare-earth transition-metal intermetallics is investigated by extending the n-component vector spin model to two-sublattice magnets. Mean-field analysis shows that the influence of the rare-earth anisotropy on the mean-field Curie temperature is much smaller than expected from the low-temperature rare-earth anisotropy. The use of ultraspherical polynomials yields a generalization of the famous m(m+1)/2 power-law exponent to m(m+n−2)/(n−1).

An analysis of iron-iron interatomic distances in several rare earth transition metal intermetallics

As a part of a systematic study of the dependence of iron-iron exchange interactions on near neighbor iron-iron distances in rare earth transition metal magnetic materials, we have conducted a statistical analysis of interatomic distances in Nd2Fe17, Nd2Fe17N3, and Nd2Fe14B. Results, in general, support the notion that larger near neighbor iron-iron distances promote higher Curie temperatures. In this work, special attention has been paid to the expansion of the Nd2Fe17 lattice due to interstitial nitrogenation and the accompanying increase in the Curie temperature. Within the unit cell, the expansion of the Nd2Fe17 lattice due to nitrogenation is highly nonuniform. When nitrided, the distance between near neighbor 6c iron sites in Nd2Fe17 increases only slightly, by 0.021 Å. However, the distances between other near neighbor iron pairs separated by less than 2.45 Å increases by about 0.04 Å. The nitrogenation of Nd2Fe17 effectively reduces the number of near neighbor iron pairs separated by less than 2.45 Å by 92%. However, near neighbor interatomic distances involving the 18h sites are the most affected by nitrogenation. Consequently, the 18h site may play a major role in the enhancement of the Curie temperature due to nitrogenation.

Processing of permanent magnet materials based on rare earth-transition metal intermetallics

Abstract A compact survey is given of the processing of high-performance permanent magnet materials, which are based on the intermetallic compounds SmCo 5 , Sm 2 Co 17 and Nd 2 Fe 14 B. In addition, the present development state of magnets based on the recently discovered Sm 2 Fe 17 N 3 phase is compiled. Besides the commercial manufacturing technologies, powder metallurgy including sintering and rapid quenching, novel processing routes, i.e. mechanical alloying, hydrogen treatment and hot working of cast ingots, are also covered.

Nucleation fields and hysteresis loops of uniaxial rare earth-transition metal intermetallics in the two-sublattice model

Nucleation fields and hysteresis loops of rare earth-transition metal intermetallics are calculated taking into account different magnetocrystalline anisotropy constants of the rare earth and the transition metal sublattices and considering the exchange coupling between the two sublattices. Nucleation fields and hysteresis loops are determined for arbitrary angles between the applied field and the c-axis and for various material parameters. The case of Fe14Nd2B is discussed in some detail.

Effective intersublattice exchange couplings in rare-earth-transition-metal intermetallics from an ab initio calculation.

A method is outlined for the ab initio determination of effective intersublattice exchange couplings J RT in rare-earth-transition-metal intermetallics. The results obtained for R 2 Fe 14 B (R=Gd,Tb,Dy) and Ho 2 Fe 17 by the linear-muffin-tin-orbital theory in atomic sphere approximation are in excellent agreement with experimental data. It is shown that J RT is not exclusively determined by the exchange-correlation part, but also strongly by other contributions to the total energy

3d-5d band magnetism in rare earth-transition metal intermetallics: total and partial magnetic moments of the RFe2 (R=Gd-Yb) Laves phase compounds

The magnetic moments of the RFe2 (R=Gd-Yb) Laves phase compounds have been calculated. Agreement with published measured values for single crystals is excellent. The R 4f magnetic moments were obtained from the standard Russell-Saunders scheme but the radial 4f spin density was otherwise part of the self-consistent density functional calculation. The influence of the localized 4f magnetism upon the conduction band magnetism is examined in detail and exchange interactions extracted. The site- and angular-momentum-resolved contributions to the total conduction bands magnetic moments are calculated and shown to obey an approximate sum rule which conserves the total conduction band moment, despite the change of 4f moment, across the series.

ChemInform Abstract: Rare Earth‐Transition Metal Intermetallics as Seen by Moessbauer Spectroscopy

ChemInformVolume 21, Issue 3 Reviews ChemInform Abstract: Rare Earth-Transition Metal Intermetallics as Seen by Moessbauer Spectroscopy K. KROP, K. KROP Solid State Phys. Dep., IM AGH, 30-059 Krakow, Pol.Search for more papers by this author K. KROP, K. KROP Solid State Phys. Dep., IM AGH, 30-059 Krakow, Pol.Search for more papers by this author First published: January 16, 1990 https://doi.org/10.1002/chin.199003323Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume21, Issue3January 16, 1990 RelatedInformation

Moment formation in magnetic rare earth metal alloys

The rare earth-transition metal intermetallics of the AX 5 type present special electric and magnetic properties which are studied by cluster self consistent electronic structure calculations, including the calculation of the enhanced spin susceptibility and magnetic stability to analyze the formation of permanent moments in the material. The example chosen is GdCo 5. We conclude that the exceptional properties of these compounds are related to a large chemical bonding between the cobalt 3d electrons and the Gd 4f and 5d.