Analysis of ultrasonic anomaly in V₃Si

Abstract

V₃Si exhibits an ultrasonic anomaly when cooled well below its martensitic and superconducting transition temperatures (T_m and T_c), and a magnetic field is applied on to the sample. The anomaly is thought to be due to reorientation of microdomains formed below T_m, to energetically favourable configurations. The effect disappears when the domains are stabilised in new configurations in the presence of the magnetic field. An analysis of these results is presented in this paper by relating the ultrasonic attenuation coefficient to strain fluctuations, arising here from domain reorientations. The treatment is based on a master equation for the probability matrix whose elements yield the probabilities of transitions between domain configurations, in the presence of both the magnetic field and the stress wave. Arguments for the validity of this master equation, when the oscillatory stress is weak, are given in a longish appendix. The derived results are used to analyse, in qualitative terms, the observed experimental facts. Also, new measurements are suggested which may help interpret the experimental data in a satisfactory manner.