Professor John Gregg

Abstract:

A magnetic resonance spectrometer is described which operates between 500 MHz and 3 GHz and uses an NE72089 GaAs MESFET operating at liquid helium temperatures as the high frequency active device. Although the sensitivity is not remarkable, it compares favourably with such other techniques as are available in this frequency range and it combines small size with ease of use.

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.