Effect of surface layers on ferromagnetic resonance in thin Fe films: Ni, Co, Si, and YBa2Cu3O7−δ

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Abstract
The results of ferromagnetic resonance experiments on 10 nm polycrystalline films of Fe with very thin surface layers of Ni and Co, using Si and a high temperature superconductor (YBCO) as substrates is reported herein. An earlier fmr investigation of Fe films on YBCO showed strongly temperature dependent linewidths and resonance fields but only small effects in Fe on Si. In this work, the resonance of Fe on Si is found to be significantly narrower when the Fe film has thin (0.5 to 1.0 nm) Ni surface layers, compared to uncoated Fe; linewidths are as narrow as 15 Oe at 9 GHz. However, when YBCO substrates are used, the iron resonance properties are nearly the same as in the case where no Ni was used. This indicates that the effects seen in earlier work were not the result of an oxide layer on the Fe but may indicate a magnetically active surface layer in the YBCO. Co surface layers have the effect of producing strongly temperature dependent anisotropies and linewidths on all substrates used, with the strongest temperature dependence near 160 K, possibly caused by the ordering of an antiferromagnetic surface layer.