Exchange Coupled NiFe/NiMn Bilayer Studied by a Vector Network Analyzer Ferromagnetic Resonance

Using cavity ferromagnetic resonance and vector network analyzer ferromagnetic resonance unidirectional, uniaxial and rotatable anisotropies were determined in permalloy(30 nm)/NiMn(56 nm). Resonance field dependence on in-plane angle clearly shows unidirectional and uniaxial anisotropy. Rotatable anisotropy, which acts as internal magnetic field independent of a direction of external magnetic field, is observed on vector network analyzer ferromagnetic resonance as upward shift of the resonance frequency of Py/NiMn compared to Py film. Even for a small exchange bias field, this shift is significantly large.