Crystallographic and magnetic investigations of the intermetallic system ErCo 2-ErAl 2

Abstract

The crystalline structure and magnetic properties of polycrystalline ErCo 2-ErAl 2 Laves phase compounds with the C14 and C15 crystal structures were investigated. It was found that for the C15 cubic structure it is possible to obtain compounds with a disordered structure. X-ray examination showed that for the ErCo 2 compound the exchange of cobalt atom between 8a and 16d sites is almost 1 atom per unit cell. After thermal treatment the crystal structure of the ErCo 2 compound shows a tendency towards ordering. For compounds with the hexagonal C14 structure the possibility of a layer distribution of atoms, alternately magnetic and nonmagnetic, was tested. This assumption is well satisfied by the ErCoAl compound. For this compound a certain anomaly was also observed, i.e. a small lattice constant c. Magnetic investigations indicated that the magnetic properties of the compounds investigated, particularly the Curie temperature, are markedly dependent on the degree of crystal structure ordering. For the remaining compounds with the C15 structure it was not possible to obtain fully ordered compounds but after thermal treatment they exhibit a tendency towards ordering.