Magnetostatic wave propagation losses in thorium-substituted YIG

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Abstract
YIG films were grown with thorium added to the melt in varying concentrations with a maximum Th/Y ratio of 0.487. The effect of the addition of thorium on the propagation of magnetostatic forward volume waves at X band was studied using a differential path delay line. It was found that the addition of thorium increased the propagation loss. For Th/Y ratios greater than 0.0428, magnetostatic forward volume waves could not be detected after propagation over a 1-cm path length. Although the variations in thorium content resulted in a range of lattice mismatches including both positive and negative values, there was no observable minimum in the loss corresponding to zero mismatch. It was also observed that the addition of thorium increased the dc conductivity, but calculations showed that the conductivity was not large enough to produce significant eddy current losses. We feel that the addition of thorium increased the amount of Fe2+ present in the films, thus activating the valence-exchange loss mechanism.