Ferromagnetic resonance in compositionally modulated Cu-Ni thin films

Abstract

Ferromagnetic resonance at 12 GHz has been studied in some of the same compositionally modulated CuNi films on which magnetization measurements were reported recently. The best samples, e.g., a film designated [20‖10]880 (i.e, 880 repetitions of [20Å Cu on 10Å Ni]) show the 295 K resonance behavior expected for a magnetic material with an easy plane uniaxial anisotropy and a line width ΔH∼10³ Oe. As T is lowered the quantity D^rf_.≡4πM+2K/M extracted from the line position data using Kittel’s equations increases roughly linearly with decreasing T. For [10‖10] 2440, D^rf goes from ∼4 kOe at 295 K to ∼20 kOe at 80 K. This low temperature value agrees with that obtained from He temperature magnetization curves. A remarkable result of the magnetization measurements was the fact that D^dc at 4.2 K was essentially the same for [10‖10], [20‖10], and [40‖10] samples. In striking contrast, the microwave values at 80 K decrease markedly with increasing thickness of the Cu layers. Simple averaging of the resonance equations has not led to an explanation of this difference.