Dominant role of thermal magnon excitation in temperature dependence of interlayer exchange coupling: Experimental verification

Abstract

Ultrathin $\mathrm{Ni}∕\mathrm{Cu}∕\mathrm{Co}$ trilayers were deposited in ultrahigh vacuum and the ferromagnetic resonance measured in situ as a function of both, temperature and out-of-plane angle of the external field. The interlayer exchange coupling ${J}_{\mathrm{inter}}$ was then unambiguously extracted at various temperatures, entirely from the angular dependence of the resonance field positions. The temperature dependence of ${J}_{\mathrm{inter}}(T)$ follows an effective power law $A{T}^{n},n\ensuremath{\approx}1.5$. Analysis of the scaling parameter $A$ shows an oscillatory behavior with spacer thickness, as does the strength of the coupling at $T=0$. The results clearly indicate that the dominant contribution to ${J}_{\mathrm{inter}}(T)$ is due to the excitation of thermal spin waves and follows recently developed theory closely.