Transverse Ultrasonic Attenuation in Magnetic Metals

Abstract

The transverse ultrasonic attenuation due to spin fluctuations in magnetic metals is theoretically studied. Spin fluctuations with finite wave numbers cause the critical attenuation at the Néel temperatures, but the ferromagnetic spin fluctuation does not. The ratio of the attenuation coefficient for transverse sound to that for longitudinal sound near the Néel temperature is given as a function of (i) the directions of sound propagation and polarization relative to the Q vector and (ii) Q/2pf, where Q is the wave number at which the spin ordering occurs below the Néel temperature and pf is the Fermi wave number of electron. The critical attenuation in MnSi observed by Komatsubara et al. is discussed in the light of the present theory.