Ferromagnetic surface layer in amorphous YFe thin films

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Abstract
Previous FMR measurements demonstrating the presence of a thin ferromagnetic layer on a‐Y1−xFex samples have been extended to a series of evaporated films with x between 50% and 85%. In most cases the thicknesses (t) were varied by a factor of 10 or more during a single evaporation. In all of these films we observe an FMR line, with 4πM increasing with x. Furthermore, as expected from a surface layer, for fixed x the line intensity is essentially independent of t. The temperature dependences of the line width (Γ) and 4πM were studied from about 1K to 300K. Both Γ(T) and 4πM(T) exhibit maximum at about 50 to 70 K. Above 100K, M(T) reduces as T3/2 and yields a spin wave stiffness of about 100 meV Å2 varying only slightly with x. We suggest that the maxima be ascribed to coupling between the ’’stiffness’’ spins and those in the bulk of the film.