Spin Fluctuations in Concentrated Ferromagnetic Alloys

Abstract

We investigate the effect of spin fluctuations in isoelectronic alloys, A_xB_1−x, by using the self-consistent renormalization (SCR) theory combined with the coherent potential approximation (CPA). The static susceptibility, the Knight shift, K_i(i=A, B), and the nuclear spin-lattice relaxation time, T_1i, relevant to each constituent atom of the alloy are calculated as functions of concentration, x, and of the temperature, T. The relation that (γ_AⁿK_A)²T_1A=(γ_BⁿK_B)²T_1B is shown to hold irrespective of x and T, where γ_iⁿ is the nuclear-gyromagnetic ratio of the nucleus of the i-atom. Since the CPA breaks down near the critical point, at which the susceptibility diverges, we adopt the virtual-crystal approximation in place of the CPA for the study of the Curie temperature, which is given by T_c∝(x_c−x)^6⁄7 very near the critical concentration, x_c. Numerical calculations are made for the electron-gas model.