We report on the temperature dependence of ferromagnetic resonance ͑FMR͒ measurements on NiFe/FeMn bilayer. This includes investigations about the angular distribution of the resonance, H R , and that of the linewidth, ⌬H. By considering the domain-wall formation model, the exchange-bias field, H EB,FMR , is derived from the FMR measurements. The disagreements observed at low temperature between these values and the ones obtained from superconducting quantum interference device measurements, H EB,SQUID , are discussed. We demonstrate that the negative line shift and the maximum of the linewidth of the FMR line are both perfectly interpreted through the slow-relaxer mechanism. This enabled us to elucidate the intriguing question about the yielding to different values of the exchange-bias anisotropy by both techniques.

Ferromagnetic resonance ͑FMR͒ 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.

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Abstract.A new analysis method of the magnetization dispersion in a thin magnetic film is presented. It is based on the angular measurement of the permeability spectra and on the evaluation of the integral relation. It provides the average orientation of the magnetization in the layer and a dispersion parameter which quantifies the magnetic dispersion. The method is successfully applied on a soft CoNbZr 800nm magnetic layer which possesses a helical anisotropy profile. This helical profile is obtained by rotating continuously the sample during the sputtering deposition on a scale from R = 0 to 16 turns. The study reveals that, for about 1/2 turn, a maximal dispersion is achieved and, for more elevated rotation speed, the magnetization no longer follows the anisotropy profile but lines up along an easiest axis direction. The experimental data are well described by a one-dimensional micromagnetic model which takes both exchange coupling and a helical anisotropy into account. The analytical cases with an exchange constant null and infinite are also considered in order to gain more insight onto the observed magnetic behaviour in the soft magnetic thin film.