Pressure-Effect Measurements Using a Vibrating-Coil Magnetometer

A vibrating-coil magnetometer used in conjunction with a helium-gas pressure-generating system has proved to be a versatile new means of studying the effects of hydrostatic pressure on magnetic properties. The sensitivity of this system permits the measurement of paramagnetic susceptibilities on powder samples of the order of 0.1 g. Paramagnetic measurements on MnAs, which undergoes a hexagonal-orthorhombic transition upon application of pressure, have directly established that the transition is accompanied by a change of the manganese ions from a high-spin to a low-spin state. Regions in the pressure-temperature space in which the high-pressure (orthorhombic) phase is metamagnetic and ferromagnetic have been delineated. In addition, the pressure dependence of the magnetic-ordering transition temperature has been determined for a number of materials, and the results are consistent with the predictions of Good-enough where applicable. Finally, it has been established that this instrument can be used to study the effect of pressure on magnetic anisotropy.