EXCHANGE STIFFNESS CONSTANT AND WALL ENERGY DENSITY OF AMORPHOUS GDTB-FECO THIN-FILMS

The exchange stiffness constant A of evaporated (Gd,Tb)-(Fe,Co) amorph ous alloys with constant Curie temperature of 465 +/- 25 K was determi ned with two different methods for a large composition and temperature range. One is the excitation of standing spin waves using Brillouin l ight scattering. The other method is the deviation of A from measureme nts of the wall energy density sigma(w) and the uniaxial anisotropy K( u) using the Bloch wall energy equation. Sigma(w) could be determined from the applied magnetic field difference for collapsing and expandin g of thermomagnetically written domains. The compositional and experim ental limits of this method are described. The uniaxial anisotropy K(u ) was measured with a torque magnetometer. In GdTb-FeCo the resulting exchange stiffness constant of A =(2.6+/-0.6)X10(-12) J/m was found to be independent of the Th content. The results obtained from Brillouin light-scattering measurements on Gd21.2Co78.8 and Gd13.5Tb6.2Fe80.3 a re in good agreement.