Influence of nonstoichiometry on the magnetic properties of CeFe$_2$ : Mn alloys

Experimental dependences of the spontaneous magnetic moment per $3d$ atom on the impurity concentration for doped CeFe$_2$ : Mn alloys are surprising. The concentration dependences of the spin magnetic moment $\mu$($3d$-Fe$^{\text{eff}}$) of the $3d$ shell of the effective Fe site in the Ce$_{1-\alpha}$Fe$_{2-\beta-x}$Mn$_x$ Laves phases have been calculated in the coherent potential approximation. It has been shown that a decrease in $\mu$($3d$-Fe$^{\text{eff}}$) is stimulated only by the presence of vacancies in the Fe($\beta$) sublattice. On the contrary, the presence of Mn impurity atoms at Fe($x$) sites and vacancies at Ce($\alpha$) sites increases $\mu$($3d$-Fe$^{\text{eff}}$). Compositions with a certain set of vacancies and a relation between their concentrations and the concentration of the Mn impurity have been proposed that make it possible to describe for the first time the experimental tendencies of the anomalous changes in $\mu$($3d$-Fe$^{\text{eff}}$) in CeFe$_2$ : Mn.