Broadband Ferromagnetic Resonance Characterization of Anisotropies and Relaxation in Exchange-biased IrMn/CoFe Bilayers

The magnetization dynamics of exchange-biased IrMn/CoFe bilayers have been investigated using broadband and in-plane angle-dependent ferromagnetic resonance spectroscopy. The interface energy of the exchange bias effect in these bilayers exceeds values previously reported for metallic antiferromagnets. A strong perpendicular magnetic anisotropy and a small in-plane uniaxial anisotropy are also observed in these films. The magnetization relaxation of the bilayers has a strong unidirectional contribution, which is in part caused by two-magnon scattering. However, a detailed analysis of in-plane angle– and thickness-dependent linewidth data strongly suggests the presence of a previously undescribed unidirectional relaxation mechanism.