Brillouin light scattering study of the spin wave stiffness parameter in Sc-substituted lutetium-yttrium iron garnet

The spin wave exchange stiffness coefficient has been measured for a series of Sc substituted lutetium-yttrium iron garnet (YIG) liquid phase epitaxy thin films. Results were obtained for a range of scandium substitutions, 0 < y < 0.83, based on the formula (Y3-xLux)[Fe2-yScy]Fe3O12. The exchange determinations were based on magnetization data and spin wave dispersion measurements by Brillouin light scattering. Scandium substitution results in a rapid decrease in the exchange stiffness from the value for pure YIG; the stiffness decreases to zero at approximately y = 1. The observed variation of the exchange stiffness as a function of y is in general agreement with theory and with previous microwave data.