Structural, magnetic and magnetocaloric properties of Fe-Ga alloys

Based on the first principle calculations, the magnetic and thermodynamic characteristics of the D03 and L12 crystal structures of Fe${}_{100-x}$Ga${}_x$ alloys (x = 25, 26.56, 28.125 at.%) were calculated by the Monte Carlo simulations. It is shown that the temperature dependences of the heat capacity contain peaks in the high-temperature region corresponding to the ferromagnet-paramagnet magnetic transition. The temperatures of the structural phase transition L1${}_2 \to$ D0${}_3$ are estimated by the intersection of the free energy curves. The Curie temperatures have been determined for the investigated structures under the temperature dependences of the magnetizations. In general, an addition of nonmagnetic Ga atoms shifts the Curie and structural phase transition temperatures to the low-temperature region. The largest direct magnetocaloric effect $\Delta $T${}_{ad.}$ = 1.55 K is predicted for the L1${}_2$ phase in the Fe${}_{75}$Ga$_{25}$ composition.