A survey is given of the physical properties, composition and crystal structure of intermetallic compounds formed between rare-earth elements and 3d transition elements. Apart from binary compounds the results of pseudobinary series are also considered. The magnetic properties determined by the exchange interactions involving 4f as well as 3d electrons, are discussed together with experimental results available on magnetovolume effects and various resonance techniques such as NMR and the Mossbauer effect.

https://iopscience.iop.org/article/10.1088/0034-4885/40/10/002/pdf

Intermetallic compounds of rare-earth and 3d transition metals

Publisher Summary This chapter provides an overview of the magnetoelastic properties of the highly magnetostrictive rare earth-Fe2 alloys. The chapter describes a general treatment of magnetostriction for the cases of hexagonal and cubic symmetry, which is applicable to the rare earth elements and the rare earth-iron compounds. The chapter presents the magnetostriction of binary rare earth-iron alloys and the magnetostriction of single crystal and polycrystal RFe2 compounds are compared to other magnetostrictive materials at room temperature. The chapter discusses a possible source of startling magnetostriction anisotropy, measurements of magnetization, sublattice magnetization, and magnetic anisotropy, and the role of intrinsic as well as extrinsic effects. It reports the effects of the strong magnetoelastic coupling on sound velocities and elastic moduli and observes extraordinarily large ∆E effects and changes in sound velocity in single crystals, polycrystals, and amorphous rare earth-Fe2 alloys. The chapter concludes with a discussion of the recent measurements of linear and volume magnetostriction on the amorphous form of the RFe2 alloys.

Chapter 7 Magnetostrictive rare earth-Fe2 compounds

By the early 1960’s, it was widely recognized that the rare earths possessed many extraordinary magnetic properties. Neutron diffraction measurements, for example, showed that the spin structures were much more complex than those of any of the classical ferromagnets or antiferromagnets. More importantly, in the heavy rare earth metals, the parallel coupling of large orbital and large spin angular momenta yielded huge magnetic moments of 9μ B and 10μ B, dwarfing the conventional values of 0.6 for Ni and 2.2 for Fe. Enormous magnetic anisotropies were also encountered in the heavy rare earth elements. In 1963, a breakthrough in magnetostrictive materials occurred with the measurement of the basal plane magnetostrictions of Tb and Dy at low temperatures (Legvold et al. 1963, Clark et al. 1963, 1965, Rhyne and Legvold 1965). These basal plane strains are 100 to 10000 times typical magnetostrictions and still remain today the largest known (~1%). Over wide temperature ranges, thermal expansions are dominated by the temperature dependences of the magnetostrains. Elastic moduli were found to be strongly influenced by the unprecedented magnetoelastic interactions. However, because of the low ordering temperatures of the rare earths the application of these magnetostrictive properties to devices operating at room temperature could not be achieved with the elements. Only Gd, which is essentially non-magnetostrictive, possesses a Curie point as high as room temperature.

Magnetostrictive Rare Earth-Fe2 Compounds

Publisher Summary This chapter discusses the magnetic properties of binary rare-earth 3d-transition-metal intermetallic compounds The basic concepts related to the intrinsic magnetic properties of the 3d-rich R n T m (R = rare earths; T = 3d heavy transition metals Mn, Fe, Co, Ni) intermetallic compounds are discussed The study of rare-earth transition-metal intermetallic compounds has a number of interesting aspects Owing to the wide range of intermetallics and their different stoichiometries and variable rare-earth elements, modifications of magnetic properties of 3d transition-metal and 4f rare-earth ions can be investigated systematically These investigations illuminate the complex interactions in which the 3d and 4f electrons are involved The rare-earth metals in their ‘normal’ state where the magnetic properties of the ion cores are well defined The 4f electrons are positioned within the ion cores and hybridization with the conduction-band-electron states is negligible This situation is realized for most iron- and cobalt-based compounds with 4f elements The Ce and Yb ions, which sometimes demonstrate unusual properties connected with valence fluctuations, tend to behave quite normally in the compounds with iron or cobalt Nevertheless, there are some anomalies in the Ce compounds that can be ascribed to a mixed-valence state of the cerium ion

Chapter 5 Magnetic properties of binary rare-earth 3d-transition-metal intermetallic compounds

Publisher Summary This chapter discusses rare earth compounds. The number of stable binary intermetallic compounds in which one of the components is a rare earth element is of the order of a thousand. Combination with elements of much smaller metallic radii then encompasses a much larger number of possible atomic arrangements of sufficiently high space filling than would be the case for two components of almost equal size. A meaningful study of the physical properties of intermetallic compounds can only be made on single phase materials. Only a fraction of the compounds is in single phase condition after the melting together of the components. The chapter explains the compounds with non-magnetic elements and compounds with d-transition metals. It also explains ternary compounds or hydrides.

Chapter 4 Rare earth compounds

Ultrasonic-sound velocity measurements have been used in order to determine the elastic moduli of polycrystalline rare-earth-iron Laves compounds $R{\mathrm{Fe}}_{2}$ ($R=\mathrm{Ce}, \mathrm{Gd}, \mathrm{Tb}, \mathrm{Dy}, \mathrm{Dy}, \mathrm{Ho}, \mathrm{Er}$) and Y${\mathrm{Fe}}_{2}$ between 4.2 and 300 K. The $\ensuremath{\Delta}E$ effect of these compounds was determined in external magnetic field up to 25 kOe. No saturation was reached at this field in Dy${\mathrm{Fe}}_{2}$ and Tb${\mathrm{Fe}}_{2}$. The anomalies in the elastic behavior of Ce${\mathrm{Fe}}_{2}$ and Ho${\mathrm{Fe}}_{2}$ were interpreted in terms of changes occurring in their magnetic structure. The results reveal the high sensitivity of the elastic constants to such changes.

Elastic and magnetoelastic properties of polycrystalline rare-earth-iron Laves compounds

The temperature and magnetic field dependence of the elastic moduli of Sm${\mathrm{Fe}}_{2}$ Laves phase compound has been investigated by means of an ultrasonic-pulse technique at a frequency of 10 MHz. The spin reorientation from the high-temperature easy direction of magnetization [111] to the low-temperature easy axis directed along [110], was observed to occur at ${T}_{sr}=195$ \ifmmode^\circ\else\textdegree\fi{}K. The behavior of the elastic moduli near ${T}_{sr}$ suggests a first-order phase change. Applied magnetic fields strongly affect the temperature dependence and the absolute values of the elastic moduli of Sm${\mathrm{Fe}}_{2}$. The elastic moduli increase significantly with increased magnetic fields, yielding a low and temperature-independent adiabatic compressibility. A remarkably high (42%) $\ensuremath{\Delta}E$ effect was observed in Sm${\mathrm{Fe}}_{2}$ at room temperature, 10-MHz ultrasonic frequency, and an applied magnetic field of 25 kOe. The magnetostriction of Sm${\mathrm{Fe}}_{2}$ is high and negative. For a field of 25 kOe at room temperature and 77 \ifmmode^\circ\else\textdegree\fi{}K values are -2100 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}6}$ and -3340 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}6}$, respectively. The limiting value of the Debye temperatures were found to be 200 and 212 \ifmmode^\circ\else\textdegree\fi{}K, for the unmagnetized and at 25 kOe, respectively.

Magnetoelasticity in Sm Fe 2

The magnetic anisotropy properties of $^{57}\mathrm{Fe}$-doped Nd${\mathrm{Co}}_{2}$ and Ho${\mathrm{Co}}_{2}$ were studied by means of M\"ossbauer spectroscopy in the 4.2-300 K temperature range. The experimental results indicate the presence of spin reorientations taking place at 43.5 and 16 K, for Nd${\mathrm{Co}}_{2}$ and Ho${\mathrm{Co}}_{2}$, respectively. Single-ion-model crystal-field calculations account for the experimental results and allow the determination of the crystal-field parameters.

U. Atzmony

Papers

Elastic and magnetoelastic properties of polycrystalline rare-earth-iron Laves compounds

Magnetoelasticity in Sm Fe 2

Crystal-field-induced spin rotations in Nd Co 2 and Ho Co 2 : A Mössbauer study

Spin-orientation diagram of the pseudobinary Tb 1-x Dy x Fe 2 Laves compounds

Ferrimagnetism in SmFe2