Dynamics over 4 GHz of spring-magnet type NiFe/CoFe bilayers with high permeability

Summary form only given. Bilayers of spring-magnet type with soft and hard layers such as NiFe/Co and NiFe/CoFe for pinned and free layers are a key structure of GMR spin-valves transducers. Advanced magnetics for integrated micro-inductors and transformers or for magnetic write heads required for ultrahigh density recording imply soft high saturation magnetization 4/spl pi/M/sub s/ with large real part /spl mu/\´ at high frequency up to or higher one GHz. CoFe alloys with the highest 4/spl pi/M/sub s/ available until now is unsuitable due to too large coercivity. On the other hand hard/soft bi- or multilayers present alternative solution to improve the dynamics of layered structure. In the present work, we have studied the dynamical behavior a such bilayers NiFe/Co and NiFe/CoFe from their complex permeability spectra (/spl mu/\´ and /spl mu/") investigated in a broad frequency range up to 6 GHz.