Magnetic dispersion in a soft amorphous layer with a helical anisotropy profile

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.