Magnetic properties of disordered ternary alloy with competing interaction

Abstract

The magnetic properties of a disordered Ising ternary alloy ( A x B 1 - x ) 1 -rC r where both A and B represent magnetic and C non-magnetic atoms are studied theoretically using the cluster variational method. The approximate free energy is evaluated by treating exactly the interactions within the clusters of all possible configurations of atomic distribution and replacing the rest of the interaction with a variational effective field. The frustration effect is introduced by taking the exchange 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 alloy exhibits the ferromagnetic phase with complete or incomplete magnetic saturation, re-entrant behaviour or spin-glass like phase. The magnetic response of an unsaturated ferro-phase exhibits superparamagnetic like behaviour at low T. The magnetization at T = 0 of a ferro-phase and the range of x where re-entrant occurs are found to be a sensitive function of the concentration of the non-magnetic atoms. The thermal behaviour of the zero-field susceptibility of an alloy that shows a spin-glass like phase can be fitted by a formula χ -1 0( T)− χ -1 0( T g) = At′ γ (1− t′) -1 with ′ = ( T− T g)/ T. The scaling behaviour of the non-linear magnetic response for T> T g remains essentially the same for all r.