DETAILED FERROMAGNETIC-RESONANCE STUDY OF AMORPHOUS FE-RICH FE90-XCOXZR10 ALLOYS .2. CRITICAL-BEHAVIOR AND UNIAXIAL ANISOTROPY

Contrary to the earlier reports, a detailed ferromagnetic resonance (F MR) study of amorphous Fe90-xCoxZr10 alloys with 0 less than or equal to x less than or equal to 10 in the critical region shows that the cr itical exponents beta and gamma for spontaneous magnetization and init ial susceptibility, which characterize the ferromagnetic (FM)-paramagn etic (PM) phase transition at the Curie temperature T-C, possess value s that are independent of composition and close to those predicted for a three-dimensional isotropic nearest-neighbour Heisenberg ferromagne t. The fraction c of spins that participates in the FM-PM phase transi tion has a value of 11% for the alloy with x = 0 and increases with in creasing Co concentration x as c(x) - c(0) similar or equal to ax(2). In the critical region, the Landau-Lifshitz-Gilbert relaxation mechani sm dominantly contributes to the 'peak-to-peak' FMR linewidth Delta H- pp and hence Delta H-pp(T) proportional to [M(S)(T)](-1), where M(S) i s the saturation magnetization. Consistent with the results obtained i n a wide temperature range, which embraces the critical region, the La nde splitting factor g has a temperature- and composition-independent value of 2.07 +/- 0.02 while the Gilbert damping parameter lambda, alt hough temperature independent, decreases with increasing Co concentrat ion. The angular dependence of the resonance field H-res observed in b oth 'in-plane' and 'out-of-plane' sample geometries has been fitted to theoretical expressions that take into account the uniaxial anisotrop y. The uniaxial anisotropy field H-k = 2K(u)/M(S) increases with incre asing Co concentration and scales with M(S). That the uniaxial anisotr opy has its origin in the pseudo-dipolar atomic pair ordering is vindi cated by the finding that K-u proportional to M(S)(2).