Comparison of experimental and theoretical initial permeability taking into account anistropy dispersion in CoNbZr thin films (abstract)

For thin films with very well defined uniaxial anisotropy, initial permeability spectra in the hard direction may be well described by Landau–Lifshitz theory that, in the low frequency range, is reduced to μi=4πMs/Hk. But the switching process of the magnetization becomes more complex when it is dominated by local variations of the anisotropy, what is known as magnetization ripple. Then, initial permeability at low frequency may be expressed as μi=4πMs/Heff. Here, effective field Heff is, from ripple theory: Heff=Hk(1+b+c), the terms b and c being additional anisotropy fields due to short and long range magnetization fluctuations. Measurements of Hk, b, and c can be obtained from the transverse bias permeability that has been measured along easy and hard axis by transverse Kerr effect. We obtain values of b+c between 0.04 and 0.30, what imply a reduction of permeability between 4% and 30% due to the dispersion of the anisotropy. Saturation magnetization was measured using a VSM and also with a computer ai...