Exchange stiffness constant and wall energy density of amorphous GdTbhyphen;FeCo thin films

摘要

The exchange stiffness constantAof evaporated (Gd,Tb)hyphen;(Fe,Co) amorphous alloys with constant Curie temperature of 465plusmn;25 K was determined with two different methods for a large composition and temperature range. One is the excitation of standing spin waves using Brillouin light scattering. The other method is the deviation ofAfrom measurements of the wall energy density sgr;wand the uniaxial anisotropyKuusing the Bloch wall energy equation. sgr;wcould be determined from the applied magnetic field difference for collapsing and expanding of thermomagnetically written domains. The compositional and experimental limits of this method are described. The uniaxial anisotropyKuwas measured with a torque magnetometer. In GdTbhyphen;FeCo the resulting exchange stiffness constant ofA=(2.6plusmn;0.6)times;10minus;12J/m was found to be independent of the Tb content. The results obtained from Brillouin lighthyphen;scattering measurements on Gd21.2Co78.8and Gd13.5Tb6.2Fe80.3are in good agreement.