Ferromagnetic resonance in compositionally modulated Cu-Ni thin films

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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 Drf.≡4πM+2K/M extracted from the line position data using Kittel’s equations increases roughly linearly with decreasing T. For [10‖10] 2440, Drf 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 Ddc 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.

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