Magnetization dynamics of soft films with thickness-dependent anisotropy

Abstract

The static and dynamic magnetic properties of samples consisting of two soft magnetic layers with in-plane easy axes at right angles are studied by micromagnetics and experiments. A one-dimensional micromagnetic model is developed, and solved quasianalytically for statics and dynamics. In particular, it is shown that the magnetic permeability arises from a set of eigenmodes, each with a macrospin ͑or gyromagnetic͒ response, that are excited differently depending on ac field orientation. Experiments ͑magnetization curves, permeability under field and in several directions͒ on cobalt-based amorphous alloy bilayers are well reproduced by the model with a single set of parameters. Such samples are therefore model one-dimensional nonuniform magnetic systems, simple yet with a rich behavior, for statics and dynamics.

Domain and wall structures in films with helical magnetization profile

“…2 shows the measured hysteresis loops along the x direction (close to the easy axis of the first layer) and the y direction (close to the easy axis of the second layer). Both magnetization curves display a break that is linked to the crossed anisotropies structure, as discussed before [11]. The bilayer is not completely symmetric as the magnetization curves are not superimposed and the remanences M r differ slightly.…”

“…The saturation magnetization M s was found close to 690 kA/m (m 0 M s ¼ 0:8 T). Spatially averaged static and dynamic magnetic properties of such samples have been reported elsewhere [11], together with their interpretation with a 1D micromagnetic model of the helix structure.…”

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

“…It is based on the angular evaluation of the integral criterion [6]. In contrast to the method recently proposed by Dubuget et al [4], the analysis here is based on the whole permeability spectra and no particular law of magnetization dispersion is required. The method proposed here gives the average orientation of the magnetization and a dispersion parameter D which quantifies the magnetization dispersion.…”

“…Hence the orientation  K of the anisotropy axis is a linear function of the position z into the thickness t while the associated anisotropy constant remains unchanged K(z) = K. Following Ref. 4, the total micromagnetic energy density can be written as:…”

“…This treatment type can induce a drastic diminution of the effective anisotropy by randomizing the anisotropy axis. Another way is to use two crossed-anisotropy layers or to generate a domain-wall in a sandwiched-ferromagnet [4,5]. These last two systems have revealed unusual behaviors.…”