A study of ultrasonic velocity and attenuation on polycrystalline Ni-Zn ferrites

Abstract

Polycrystalline NiZn ferrites with different grain sizes (1·2 μm to 10·2 μm) were prepared by the usual ceramic method. The magnetic properties were measured at room temperature. The ultrasonic velocity and attenuation were measured on Ni-Zn ferrite by using the pulse transmission method at 1 MHz, in the temperature range 300-600 K. The velocity was found to be slightly sample dependent at room temperature and decreased with increasing temperature, except near the Curie temperature, Tc, where a small anomaly was observed. The longitudinal attenuation (α1) at room temperature was found to be more sample dependent. The temperature variation of ultrasonic longitudinal attenuation exhibited a broad maximum around 400 K and a sharp maximum just below Curie temperature (Tc). The above observations were carried out in the demagnetized state. The application of a 380 mT magnetic field allowed us to reach the saturated state of the sample at all the measuring temperatures. The anomaly observed in the thermal variation of velocities (longitudinal and transverse) and attenuation has been qualitatively explained with the help of the temperature variation of the magneto-crystalline anisotropy constant.