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.
Highlights
Soft ferromagnetic thin films possess high permeability levels, a magnetic property which is largely used in lots of high frequency applications such as planar inductance, microwave filters or antiheft devices
For φ = 86°, no signal is measured given that hRF is along a well-defined easy axis
For the 0-turn sample, the minimum of I(φ)/Imax is observed at φ = 86° in agreement with an easy axis direction expected along the y axis
Summary
Soft ferromagnetic thin films possess high permeability levels, a magnetic property which is largely used in lots of high frequency applications such as planar inductance, microwave filters or antiheft devices. The potentialities of the soft ferromagnetic materials can be evaluated by the generalized Snoek's law and the integral criterion equation The former describes the existence of a tradeoff between high permeability levels and high operating frequencies, while the latter establishes that the integral of μ'' f df is bounded by the square of saturation magnetization multiplied by a constant [1,2]. One way consists in applying a rotating static magnetic field during annealing [3] 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]. The results are compared with a one-dimensional (1D) micromagnetic model which simulates the static state of the magnetization in the thickness of a helical anisotropy sample and the associated microwave permeability spectra
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