Dynamic magnetic properties of Fe70Co30(100) single-crystal thin films deposited at various substrate temperatures

Abstract

Crystallographic orientation dependence of Gilbert damping constant, α, has been measured under different static magnetic fields for Fe70Co30(100) single-crystal thin film samples prepared at various substrate temperatures. Lorentz type resonance peaks are observed for the samples prepared below 200 ºC. For a sample deposited at 400 ºC, broadening of the resonance peak is observed, which is related with an increased surface roughness. α value decreases monotonically with increasing the static field when the field is applied parallel to the easy magnetization axis, whereas it increases when the field is applied along the hard magnetization axis up to around the anisotropy field and then decreases. The minimum value of α is determined to be 0.012 for the hard axis under static fields greater than 650 Oe. The value is twice larger compared with that of Fe(100) single-crystal film. The static magnetization curves measured for Fe70Co30 films show large deviations from the curves expected by coherent rotation mode. Such deviation seems to be a possible reason for a larger α value of Fe70Co30 thin film.