Physical Acoustics: Volume V

In the last decade ultrasonic techniques have been used extensively in solidstate research. The impetus to this activity came from Bommel's discoveries of (a) the dramatic decrease in the ultrasonic attenuation which occurs when a metal becomes superconducting (Bommel, 1954) and (b) the oscillatory variation of the attenuation as a function of magnetic field which is observed in pure metals at low temperatures (Bommel, 1955). The physical basis of these two important effects was already understood in the late fifties, and subsequently these phenomena were used as tools in studies of superconductivity and the Fermi surfaces of metals. During the last few years other types of ultrasonic phenomena were discovered in metals, paramagnets, ferrites, and high-field superconductors. Each of these discoveries opened a new avenue of research in the field of ultrasonics.