Brilliouin light scattering determination of the spin-wave stiffness parameter in lithium-zinc ferrite

The spin-wave stiffness parameter for Zn substituted Li-ferrite has been measured by the technique of Brillouin light scattering. A range of compositions from pure Li-ferrite through Li-Zn ferrite with 0.65 Zn at./formula unit was studied. The magnon frequency vs. field determinations from light scattering and separate magnetization data were used to determine the spin-wave stiffness parameter, D. The data give a D-value of 10.1 × 10^-9Oe.cm²for pure lithium ferrite, approximately twice as large as for yttrium iron garnet. A rapid decrease occurs with Zn substitution and D is essentially zero for about 0.4 Zn at./formula unit. These are the first reported results of Brillouin scattering from a polycrystalline ferrite. A molecular field calculation of the spin-wave stiffness yields a much slower decrease in D with zinc than is found experimentally.