Temperature dependence of magnetic properties of AF-biased CoFe films with high FMR

We investigate the temperature dependence of static and dynamic magnetic properties of AF/F/AF multilayers consisting in NiMn as AF-layer and Co/sub 90/Fe/sub 10/, Co/sub 50/Fe/sub 50/ and Co/sub 35/Fe/sub 65/ as F-layer, respectively. The T-dependences of the hysteresis loops have been analyzed in relation with the corresponding microwave permeability spectra. The results indicate a lowering of both the exchange bias (Hex) and the anisotropy field (Hk dc) above 150/spl deg/C, in agreement with blocking temperature considerations from literature. However, microwave characterizations show better high temperature stability, with a shift of ferromagnetic resonance frequency less than 20% up to 300/spl deg/C. This reveals a strong discrepancy between the anisotropy field from the static and dynamic measurements including the T-dependence. Finally, this work points out unexpected excellent temperature stability up to 300/spl deg/C proving that such multilayers are available for future use in RF devices at very high frequencies.