ELECTRONIC-STRUCTURE AND MAGNETISM OF YCO5, YNI5 AND YCO3NI2

Dependences of the magnetic moment on the lattice constant for binary and pseudobinary compounds YCo5, YNi5 and Y(Co0.6Ni0.4)(5) With a hexa gonal CaCu5-type structure are studied by an ab initio calculation on a self-consistent linear muffin-tin orbital method within the atomic s phere approximation. It is found that Co moments in YCo5 decrease abru ptly at a critical lattice constant smaller than the observed one. On the other hand, Ni moments in YNi5 are shown to appear at a lattice co nstant a little larger than the observed one. Similar calculations are carried out for the ordered compound YCo3Ni2, where Co and Ni atoms o ccupy the 3g and 2c sites, respectively. It is shown that Co and Ni at oms in this compound lose their moments at a lattice constant slightly smaller than the observed one. It is also found that the Co atom on t he 3g site in YCo5 and YCo3Ni2 has two magnetic states, a high-moment state and a low-moment or non-magnetic state, depending on the lattice constant. The present results explain the concentration dependence of the the bulk moment observed for Y(Co1-xNix)(5) and La(Co1-xNix)(5).