Ultrasonic attenuation and thermal expansion of single crystalline cobalt ferrous ferrites

Based on the acoustic loss measurements on a series of CoFe single crystal ferrites three relaxation mechanisms at 100, 420 and 570 K were identified with the respective activation energies of 0.03, 0.3 and 0.9 eV. The electronic transitions between iron ions, and iron and cobalt ions are responsible for the first two while the ionic diffusion of Fe/Co via octahedral vacancies is the origin of the third relaxation mechanism. The observed hysteresis in the thermal dilatation measurements between 700 and 800 K points to a redistribution of Fe and Co ions among the octahedral and tetrahedral sites of the spinel structure