TEMPERATURE-DEPENDENCE OF THE MAGNETIC EXCITATIONS IN ORDERED AND DISORDERED FE72PT28

We have performed inelastic neutron scattering measurements of the lon g-wavelength spin wave excitations of both ordered and disordered Fe72 Pt28 single crystals below their critical temperatures, T(C)=510 and 3 75 K, respectively. The spin waves followed the expected E=Dq2 depende nce,and the temperature-dependent spin stiffness D decreased as (T/T(C ))5/2, as expected for an isotropic ferromagnet. The extrapolated zero -temperature spin stiffness was D = 98(4) meV angstrom2 and 107(1) meV angstrom2 for the disordered and ordered alloy, respectively. These v alues are significantly higher than the zero-temperature stiffness as determined by magnetization measurements.