EFFECT OF SURFACE-LAYERS ON FERROMAGNETIC-RESONANCE IN THIN FE FILMS - NI, CO, SI, AND YBA2CU3O7-DELTA

The results of ferromagnetic resonance experiments on 10 nm polycrysta lline films of Fe with very thin surface layers of Ni and Co, using Si and a high temperature superconductor (YBCO) as substrates is reporte d herein. An earlier fmr investigation of Fe films on YBCO showed stro ngly temperature dependent linewidths and resonance fields but only sm all effects in Fe on Si. In this work, the resonance of Fe on Si is fo und 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 nar row as 15 Oe at 9 GHz. However, when YBCO substrates are used, the iro n 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 no t the result of an oxide layer on the Fe but may indicate a magnetical ly active surface layer in the YBCO. Co surface layers have the effect of producing strongly temperature dependent anisotropies and linewidt hs on all substrates used, with the strongest temperature dependence n ear 160 K, possibly caused by the ordering of an antiferromagnetic sur face layer.