Ultrasonic anomalies in nickel and cobalt at elevated temperatures

Using a pulse method, the attentuation and velocity of longitudinal ultrasonic waves in nickel and cobalt are measured for frequencies 2, 3 and 6 Mc/sec from −78°c up to the Curie temperature range. At certain intermediate temperatures, peculiar peaks in attenuation accompanied by anomalies in velocity are observed. As the specimen is more and more magnetized, the peaks are found to diminish in height and suffer a slight shift towards higher temperatures. At technical magnetic saturation, the peaks do not collapse completely, a fact which differentiates the observed anomalies from those due to domain wall motion or domain rotation. An explanation for the origin of these anomalies could be found in the redistribution of spins, as an effect of the periodic mechanical stress, among the simultaneous stable directions of spontaneous magnetization inside the domain. This view is supported by a calculation of the corresponding temperatures of the peaks which agree fairly well with the experimental temperatures.