Study on dynamic and static magnetic properties of polycrystalline cobalt ferrite under bias magnetic field

Owing to their low resistivity, metal-based magnetostrictive materials are prone to eddy current loss under highfrequency magnetic field excitation, leading to a significant decline in output characteristics. Cobalt ferrite, a new non-metal-based magnetostrictive material, possesses both high magnetostriction strain and high resistivity, making it highly promising for high-frequency driving applications. However, reports on cobalt ferrite as the core driving material for ultrasonic transducers remain limited, and research on its high-frequency vibration characteristics is insufficient. In this study, magnetostrictive samples of cobalt ferrite were prepared using a solidstate reaction method, and their morphologies and magnetic properties were characterized. Under a bias magnetic field, the dynamic magnetic properties of cobalt ferrite and temperature variations with the driving magnetic field amplitude and prestress were analyzed. The results indicated that the density of the sample prepared by solid-state reaction can reach 88 % and the saturation magnetostriction coefficient lambda s can reach 186 x 10-6, with an optimal bias range of 400-600 Oe for the cobalt ferrite. When the driving magnetic field amplitude is 100 Oe in the optimal bias range, the output amplitude of the cobalt ferrite is 2160 nm, meeting the output requirement of high-frequency magnetostrictive ultrasonic transducers.