Anisotropy, wall energy density, and exchange stiffness of amorphous (Gd,Dy)-(Fe,Co) films

Abstract

The uniaxial anisotropy Ku and the magnetic domain wall energy density σw are important quantities for the thermomagnetically information storage process and its modeling. Ku was measured on (Gd,Dy)-(Fe,Co) films in dependence on temperature and Dy content. It increased linearly with increasing Dy content. Ku and the coercive field Hc are related by the equation Hc=αKun/μ0Ms with the fitting parameters α and n. At room temperature σw was determined from the difference of the switching fields for expanding and collapsing of thermomagnetically written circular domains on magneto-optical disks. The disks were prepared by electron beam evaporation with Dy contents between 5 and 35 at. %; the composition was adjusted to yield samples with a Curie temperature TC close to 500 K. The wall energy density increased with the Dy content. The exchange stiffness A was derived from measured σw and Ku data using the simple Bloch wall equation A=σw2/16Ku. The exchange stiffness was found independent on the Dy content to be 3.1×10−12±0.8×10−12 J/m. The resulting A was in agreement to literature data for amorphous Gd33Fe67 alloys.