Monte Carlo calculations of Curie temperatures of Y[formula omitted]Gd[formula omitted](Fe[formula omitted]Co[formula omitted])[formula omitted] pseudobinary system

Abstract

The close-packed AB2 structures called Laves phases constitute the largest group of intermetallic compounds. In this paper we computationally investigated the pseudo-binary Laves phase system Y1−xGdx(Fe1−yCoy)2 spanning between the YFe2, YCo2, GdFe2, and GdCo2 vertices. While the vast majority of the Y1−xGdx(Fe1−yCoy)2 phase diagram is the ferrimagnetic phase, YCo2 along with a narrow range of concentrations around it is the paramagnetic phase. We presented results obtained by Monte Carlo simulations of the Heisenberg model with parameters derived from first-principles calculations. For calculations we used the Uppsala atomistic spin dynamics (UppASD) code together with the spin-polarized relativistic Korringa–Kohn–Rostoker (SPR-KKR) code. From first principles we calculated the magnetic moments and exchange integrals for the considered pseudo-binary system, together with spin-polarized densities of states for boundary compositions. Furthermore, we showed how the compensation point with the effective zero total moment depends on the concentration in the considered ferrimagnetic phases. However, the main result of our study was the determination of the Curie temperature dependence for the system Y1−xGdx(Fe1−yCoy)2. Except for the paramagnetic region around YCo2, the predicted temperatures were in good qualitative and quantitative agreement with experimental results, which confirmed the ability of the method to predict magnetic transition temperatures for systems containing up to three different magnetic elements (Fe, Co, and Gd) simultaneously. For the Y(Fe1−yCoy)2 and Gd(Fe1−yCoy)2 systems our calculations matched the experimentally-confirmed Slater–Pauling-like behavior of TC dependence on the Co concentration. For the Y1−xGdxFe2 system we obtained, also in agreement with the experiment, a linear dependence of TC on the Gd concentration. In addition, on the example of Y0.8Gd0.2Co2 ferrimagnet, we showed the possibility of predicting the non-trivial behavior of the temperature dependence of magnetization, confirmed by comparison with previous measurement results.