A Vibrating Wire Susceptometer with a special electronic control for fast measurements at high temperatures

The measurement of the temperature behaviour of initial magnetic susceptibility is a powerful method for the thermomagnetic analysis of ferromagnetic materials. However, its application to nanostructured materials with technical relevance, particularly in the case of metastable systems, is made difficult by several conflicting conditions: the necessity to employ low magnetic fields, the required high sensitivity and the need for rapid scans in the high-temperature range. The vibrating wire susceptometer, an instrument belonging to the class of alternating gradient force magnetometers, has, in theory, the right characteristics to make such measurements. However, management of the instrument when carrying out rapid scans is intrinsically complex and requires a special electronic controller described here in detail. A combination of two phase-locked loop blocks is needed to provide the correct phase shift to ensure the locking of the resonance frequency while the instrument is working. A new measurement procedure that keeps the oscillation amplitude constant has also been implemented and it has proved to be very useful for rapid overview of the sample magnetic properties. The limitations of the controller performance due to the presence of noise are discussed. Extensive test measurements were carried out and analysed