Finite-temperature magnetism in amorphous Fe - Y alloys

Abstract

Various magnetic properties of amorphous Fe - Y alloys at finite temperatures such as the densities of states, local magnetic moments, susceptibilities, and the magnetic phase diagram have been investigated on the basis of the finite-temperature theory of amorphous magnetic alloys. It is found that the calculated magnetization, distribution of local moments, susceptibilities, and magnetic phase diagram in the most random atomic configuration show a spin-glass phase, a re-entrant spin-glass phase, ferromagnetism, and paramagnetism with reducing Fe concentration. These results describe qualitatively the experimental data for the melt-spun Fe - Y alloys. It is verified that the nonlinear magnetic couplings between Fe local moments and the large-amplitude fluctuations of local moments due to structural disorder result in the spin glass in the Fe-rich region. The decrease of the average coordination number of the Fe atom due to the large difference in atomic size between Fe and Y atoms, on the other hand, stabilizes the ferromagnetism at lower Fe concentrations. The difference in magnetic phase diagram between the melt-spun and the sputtered Fe - Y alloys is interpreted in terms of that between the atomic short-range orders.