First-principles Study of Intersite Magnetic Couplings and Curie Temperature in RFe12-xCrx (R = Y, Nd, Sm)

We present a first-principles study of RFe12-xCrx (R = Y, Nd, Sm) crystals with ThMn12 structure. We discuss, within the mean field approximation, intersite magnetic couplings calculated using Liechtenstein's formula and convert them into Curie temperatures, T-C, which are found to become larger when a small amount of Cr (x <= 0.5) is introduced into the system. This enhancement is larger than that for Co in the dilute limit, x -> 0. In contrast, above x > 0.5, the Curie temperature decreases as Cr concentration increases. This behavior is analyzed using an expansion of T-C in terms of concentration.