Abstract
The objective of this work has been to study the attenuation of microwave frequency sound in ferromagnetic nickel and iron in single crystal and polycrystalline form. From this analysis we find for magnetically saturated samples that the transmitted sound amplitude dependence on sample conductivity is dominated by an electron damping effect. An exponential dependence of transmitted sound amplitude versus sample conductivity was observed as the temperature was varied. This exponential amplitude dependence on conductivity is what is expected to be a dominant attenuation mechanism from theories for sound wave attenuation in metals. For our samples the attenuation coefficient at room temperature is of the order of 0.05 dB/$\mu m$ to 0.5 dB/$\mu m$. At low temperatures, where the product of the sound propagation constant and the electron mean free path approaches and exceeds unity, a decrease in the sound amplitude dependence on conductivity was observed, also in agreement with theory.In our experiments nickel and iron samples 9 to 19 $\mu m$ thick form part of the common wall between two microwave cavities. Microwaves at 9.4 GHz are incident on the transmitter cavity; the signal transmitted through the sample enters the receiver cavity and is subsequently detected. The amplitude of the detected signal is measured at a given temperature and applied magnetic field orientation, as a function of the applied magnetic field strength. For the applied magnetic field orientations in these experiments, transverse and longitudinal sound waves at the incident microwave frequency are generated at the sample surfaces. For thick samples it is found that the transmission is dominated by sound waves and the direct transmission of microwaves through the samples is negligible.