Professor John Gregg

Abstract:

An improved technique is described for the detection of magnetic phase transitions using acoustic waves with electrical interferometry. The method employs zinc oxide transducers sputtered directly onto the sample. These transducers operate efficiently at frequencies up to 3 GHz, corresponding to acoustic wavelengths of the order of 2 μm. By measuring the phase of high-order multiple echoes, changes in sample thickness and/or velocity of parts in 109 can be detected. The method has been used to determine the phase diagram of the metamagnet dysprosium aluminum garnet for magnetic fields parallel to [001]. General agreement with earlier determinations based on thermodynamic measurements is obtained.