Microwave acoustic relaxation losses in MgO due to Fe2+

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Abstract
The microwave acoustic attenuation has been measured in samples of single-crystal iron doped MgO, as a function of temperature, and at 0.58 GHz and 1 GHz. The attenuation of (100) propagating compressional waves exhibits a peak at approximately 30K which is attributed to relaxation between the ground state levels of Fe2+ ions on cubic sites. An analysis of the form of the peak enables the relaxation time to be determined as a function of temperature and an excited state at 110+or-2 cm-1 is derived in agreement with infrared spectroscopic measurements. The magnitude of the attenuation of the (100) compressional mode and the absence of a peak in the transverse (100) mode is in fair agreement with a model which supposes that the Fe2+ ions are subject to random static strains, which are predominantly compressional in nature.