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 Co₉₀Fe₁₀, Co₅₀Fe₅₀ and Co₃₅Fe₆₅ 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°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°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°C proving that such multilayers are available for future use in RF devices at very high frequencies.