Magnetism and related phenomena in RE(Co1-xSix)2 compounds

We report on crystal structure, magnetic, transport and dilatometric studies of the pseudobinary compounds RE(Co1-xSix)(2) with RE = Nd, Ho and Er for x less than or equal to 0.15. The lattice volume of the Ho and Er-based compounds is almost composition invariable, whereas in Nd(Co1-xSix)(2) for x between 0 and 0.15 it increases by similar to 7%. Already small Si substitutions for Co (x less than or equal to 0.075) induce a dramatic increase of T-C both in the Ho and Er compounds without apparent loss of the first order character of the magnetic phase transition, whereas opposite changes of T-C are observed in Nd analogues. These results, together with variations of resistivity and magnetovolume anomalies at T-C and of the Co magnetic moment observed in all three systems is discussed in terms of expected changes of electronic structure and their influence on the hierarchy of exchange interactions and formation of the Co moment in this class of materials. (C) 1997 Elsevier Science S.A.