Computer modeling of magnetic properties of disordered BCC phase of Fe$_{100-x}$Me$_x$ alloys (Me = AL, GA, GE)

In this paper, within the framework of density functional theory for the disordered phase $A2$ of Fe-Me alloys (Me = Al, Ga, Ge) the magnetic exchange constants $J_{ij}$ are calculated and the Curie temperatures $T_C$ are estimated in dependence of the concentration of Me = Al, Ga, Ge (in the range of $0 \leqslant x \leqslant 14 $at. %) and the crystal lattice parameter (in the range of $2,7 \leqslant a \leqslant 3,0$ Å). The $J_{ij}$ distribution obtained in the paper demonstrates non-linear behavior. The highest ferromagnetic interaction in the first coordination sphere is $\approx23$ meV. In the third coordination sphere, antiferromagnetic exchange interaction is observed, which reaches a value of $\approx -2,5$ meV. Magnetic transition temperatures calculated using the mean field approximation based on the experimental values and the $a_0$ parameters calculated within the density functional theory show the presence of a concentration range of $4 \leqslant x \leqslant 8$ at. % in which $T_C$ increases. The cross-section of the calculated Curie temperature distribution shows that for all studied Fe-Me alloys with the lattice parameter $a_0 = 2,94$ Å, it is possible to construct a dependence $T_C(x)$ that is in quality agreement with the experimental one.