Using second‐ and third‐order elastic constant data, the average Grüneisen number 〈γ〉, the average square Grüneisen constant 〈γ2〉, and the nonlinearity constant D have been calculated for yttrium iron garnet (YIG). Attenuation of ultrahigh‐frequency (500 and 1000 MHz) acoustic waves (both longitudinal and shear) propagating along 〈100〉 and 〈110〉 directions, caused by Akhieser loss and thermoelastic phenomena, have been evaluated for YIG at 300 °K. Of these, the Akhieser loss is found to be greater. For shear waves propagating in the 〈100〉 direction, the Akhieser loss accounts for about 12% of the measured loss reported in the literature at 500 MHz and about 25% at 1000 MHz.
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