MAGNETIC-PROPERTIES OF DISORDERED TERNARY ALLOY WITH COMPETING INTERACTION

The magnetic properties of a disordered Ising ternary alloy (A(x)B1-x) (1-r)C(r) where both A and B represent magnetic and C non-magnetic ato ms are studied theoretically using the cluster variational method. The approximate free energy is evaluated by treating exactly the interact ions within the clusters of all possible configurations of atomic dist ribution and replacing the rest of the interaction with a variational effective field. The frustration effect is introduced by taking the ex change integral J(AB) to be antiferromagnetic whereas J(AA), J(BB) ( < J(AA)) are ferromagnetic in nature. Depending on x, r and J(AB) the a lloy exhibits the ferromagnetic phase with complete or incomplete magn etic saturation, re-entrant behaviour or spin-glass like phase. The ma gnetic response of an unsaturated ferro-phase exhibits superparamagnet ic like behaviour at low T. The magnetization at T = 0 of a ferro-phas e and the range of x where Te-entrant occurs are found to be a sensiti ve function of the concentration of the non-magnetic atoms. The therma l behaviour of the zero-field susceptibility of an alloy that shows a spin-glass like phase can be fitted by a formula chi0(-1)(T) - chi0(-1 )(T(g)) = At('gamma)(1 - t')-1 with t' = (T - T(g))/T. The scaling beh aviour of the non-linear magnetic response for T > T(g) remains essent ially the same for all r.