Variation of domain-wall structures and magnetization ripple spectra in permalloy films with controlled uniaxial anisotropy

We have studied domain-wall structures and magnetization ripple in permalloy films with widely varying values of anisotropy field and thickness. Both the Fresnel and differential phase contrast imaging modes of Lorentz microscopy have been used, the latter proving particularly valuable for providing reliable quantitative data. Cross-tie walls were frequently observed but the density of the cross ties increased markedly with anisotropy field while the cross-tie length decreased. In accord with expectation, the mean ripple wavelength and magnitude of the ripple decreased with increasing anisotropy field, albeit the variation was more rapid than could be accounted for using simple theories. Generally the root-mean-square dispersion angle was found to be greater than that in earlier experimental work, a factor that was ascribed to the use of an incomplete analysis procedure in the past. (c) 2005 American Institute of Physics.