Temperature dependence of exchange bias in NiFe/FeMn bilayers

Ferromagnetic resonance (FMR) and dc-magnetometry measurements were used to investigate the temperature dependence of the anisotropies responsible for the exchange-bias coupling in NiFe/FeMn bilayer. At room temperature, both measurements showed the same exchange-bias angular distributions due to a low coupling strength, H(E), with respect to the antiferromagnet domain-wall formation anisotropy. The anisotropies derived from both techniques displayed identical H(E) values but different uniaxial anisotropies. This disagreement may be ascribed to different stabilities of antiferromagnetic grains in both techniques. At low temperature, strong disagreements were found on the exchange-bias values. They are explained by the occurrence of the slow relaxer mechanism in FMR experiments.