Strong Dependence of Thermal and Magnetic Properties on Valence Electron Structures in R2Co17 (R = Rare Earth) Intermetallics.

Abstract

The valence electron structures (VESs) and thermal and magnetic properties of R2Co17 intermetallics with rhombohedral (R = Ce, Pr, Nd, Sm, Gd, and Tb) and hexagonal (R = Y, Dy, Ho, and Er) structures are studied systematically with the empirical electron theory of solids and molecules (EET). The calculated values, which cover the bond length, cohesive energy, melting point, magnetic moment, and Curie temperature, fit the experimental ones well. The study reveals that the thermal and magnetic properties of R2Co17 are strongly related to their VESs. It shows that the properties of R2Co17 can be modulated by covalence electron number nc/atom for cohesive energy and melting point, the 3d magnetic electrons of various Co sublattices for magnetic moment, the electron transformation from covalence electrons to 3d magnetic electrons for the moments of various Co sublattices, and molecular moment for Curie temperature. The structural stability of R2Co17 depends upon the distribution probability of covalence electrons on various bonds. The pseudobinary La-Co 2:17 phase can be stabilized by doping a transition metal into La2Co17 by modulating the covalence electron number per Co atom to be very close to the stable nc/Co range of rhombohedral LR2Co17 (LR=light rare earth).