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

Exchange interactions in rare earth—transition metal compounds

The magnetic behaviour of rare-earth—transition metal compounds

Ferromagnetic compounds of the series ErxY1-xCo2 (x=1, 08, 07, 06) have been investigated in specific-heat, thermal-expansion, magnetisation, AC susceptibility and resistivity experiments The magnetic moment on the Co atoms decreases with decreasing Er content, as does the Curie temperature The character of the magnetic transition changes from first order to second order around x=07 This change is compared with the similar one observed in other RExY1-xCO2 compounds with RE-Gd, Tb, Dy and is discussed in terms of the Inoue-Shimizu model by taking into account the strong temperature dependence of the magnetic susceptibility of the 3d electrons The spontaneous volume magnetostriction at zero temperature, the magnetic contribution to the specific heat and the magnetic entropy below the magnetic ordering temperature are determined The experimental results for these quantities confirm the induced character of the cobalt magnetic moment in these compounds

https://iopscience.iop.org/article/10.1088/0305-4608/18/2/010/pdf

Electronic and magnetic properties of ErxY1-xCo2 compounds

Publisher Summary This chapter focuses on permanent magnet materials based on 3d-rich ternary compounds. A novel type of permanent magnet material is based on a ternary intermetallic compound obtained by combining Nd, Fe and B. Its crystal structure is tetragonal and the formula composition corresponds to Nd 2 Fe 14 B. There are two important features associated with this compound. In the first place, it is based on Fe, which is much less expensive than Co. In the second place, this compound has a crystal structure that gives rise to a crystal-field interaction in which not Sm but Nd and Pr produce a uniaxial anisotropy suitable for permanent magnet application. This means that one may profit from the ferromagnetic coupling between the Nd (Pr) and Fe moments and the comparatively high Nd moment to reach a high value for the saturation magnetization. The chapter describes basic properties of rare earth compounds of the type R 2 Fe 14 B, R 2 Co l4 B and several related intermetallic compounds. This description comprises phase relationships, crystal structure, magnetization, magnetic structure and magnetic anisotropy. The properties of all these materials and those obtained by suitable substitutions are compared and discussed in terms of magnetic exchange interaction and crystal-field interaction. The chapter also discusses permanent magnet fabrication, the various coercivity mechanisms and their relation to the microstructure, and some technological applications of NdFeB magnets.

Chapter 1 Permanent magnet materials based on 3d-rich ternary compounds

The value of 9.27 × 10−23 J for the exchange coupling parameter between the Ho and Co spins in Ho2Co17 has been derived. Some experimental evidence is given to show that the R–T spin coupling parameter is rather insensitive to the kind of the rare earth atom as well as on the cobalt composition. It allows to calculate the intersublattice molecular fields for the rare earth–cobalt intermetalic compounds. This field affects the R magnetic moment and originates from the Co sublattice in the R2Co17, RCo5, R2Co7, RCo3, and RCo2 compounds. The fields in the new magnetic materials of the R2Co14B type have also been evaluated.



Es wird ein Wert von 9,27 × 10−23 J fur den Austauschparameter zwischen den Ho- und Co-Spins in Ho2Co12 ermittelt. Aus experimentellen Daten wird geschlossen, das der R–T-Spinkopplungsparameter relativ unempfindlich gegenuber der Art der Seltenen Erde und dem Kobaltgehalt ist. Dies gestattet, die molekularen Felder der Untergitter fur die intermetallischen Verbindungen zwischen Seltenen Erden und Kobalt zu berechnen. Diese Felder beeinflussen das magnetische Moment der Seltnen-Erd-Atome und ruhren von dem Co-Untergitter in den Verbindungen R2Co17, RCo5, R2Co7, RCo3 und RCo2 her. Die Felder in den neuen magnetische Materialien vom Typ R2Co14B werden ebenfalls berechnet.

R. J. Radwański

Papers

The Intersublattice Molecular Fields in the Rare Earth–Cobalt Intermetallics