MAGNETIC-PROPERTIES OF (Y,LU)(CO,AL)(2)

A drastic change in the magnetic ground state observed for pseudobinar y compounds (Y1-tLut)(Co0.88Al0.12)(2) with cubic Laves phase structur e is discussed by making use of the phenomenological Landau energy exp anded up to the eighth power of magnetization. The dependence of Landa u coefficients on Lu concentration is determined from observed results of the spontaneous magnetization and the critical field of a metamagn etic transition. It is explicitly shown that small changes in the Land au coefficients leads to the transition from a weakly to strongly ferr omagnetic state. The 'lutetium paradox', that the observed Curie tempe rature of Lu(Co, Al), is higher than that of analogous compounds with some heavy rare-earth elements, is also discussed in the present theor y.