FMR STUDY OF CHANGES IN THE MAGNETIC-BEHAVIOR OF AMORPHOUS FE83-XWXB17 (X=5, 9) ALLOYS DUE TO ISOTHERMAL ANNEALING .2. IN THE CRITICAL REGION

Extensive ferromagnetic resonance (FMR) measurements have been perform ed in the critical region, -0.15 less-than-or-equal-to epsilon = (T - T(C))/T(C) less-than-or-equal-to 0.15, on amorphous Fe78W5B17 and Fe74 W9B17 alloys, before and after they had undergone isothermal annealing treatment at a temperature T(A) = 400 K for durations of time t(A) = 1 and 2 h. The values of saturation magnetisation, M(s), and resonance field, H(res), at different temperatures are accurately determined th rough an elaborate lineshape analysis of the observed FMR spectra. Fro m the M(s)(H(res), T) data so obtained, the asymptotic values of the c ritical exponents beta and gamma for spontaneous magnetisation and ini tial susceptibility are estimated using the 'range-of-fit' scaling-equ ation-of-state analysis. Consistent with the predictions of the infini te three-dimensional (3D) ferromagnetic (FM) matrix plus finite spin c lusters model and with the well-known Harris criterion, isothermal ann ealing, which enhances the value of the Curie temperature, T(C), consi derably, leaves the values of the exponents unaltered from their 'as-q uenched' values, which are close to those predicted by 3D nearest-neig hbour Heisenberg model. In the critical region, the Gilbert damping pa rameter and the Lande splitting factor are temperature-independent and structural relaxation has no effect on them.