Influence of a helical anisotropy profile on the static and dynamic properties of a soft magnetic layer

The static and dynamic properties of a soft magnetic layer presenting a helical anisotropy profile have been studied both experimentally and theoretically with the help of one-dimensional (1D) micromagnetic calculations. The aim is to investigate the possibility of achieving an evanescent anisotropy by randomizing the effective anisotropy thanks to a continuous rotation of the samples during a growth process. A general method to evaluate the magnetization dispersion based on the angular measurement of the complex permeability spectra and on the determination of the integral criterion is presented. The maximum randomization of the magnetization in Co86Nb10.5Zr3.5 layers is found for the sample rotated 1/2 turn. A significant decrease of the effective anisotropy from 15 to 7 Oe is obtained. The 1D simulations give a good explanation and description of the angular dispersive behavior of the magnetization observed as a function of the rotation speed imposed during growth. However, a discrepancy between measured and calculated resonance frequencies is observed and attributed to short-range fluctuations of the magnetization known as the ripplelike phenomenon. Compared to literature, this effect is particularly strong for a high rotation speed.