Automatic Temperature Calibration During Swept Temperature Magnetisation Measurements

Abstract

Most temperature controllers overshoot when changing temperature, which causes major problems in measuring the magnetisation of hysteretic superconductors. Continuous sweeping avoids this problem but introduces lags between sample temperature and the thermometer which vary for different sample sizes and materials. A common way to allow for temperature lags is to do the experiment at different sweep rates and extrapolate to zero sweep rate. It is shown that this is an inefficient and time consuming solution and that a better method is to impose a ripple temperature variation on the sweep. The variation of the amplitude and phase of the ripple in the magnetisation give enough information for the thermal time constants to be determined at the same time as the average magnetisation is being measured. The temperature can be corrected for any sample during the course of a magnetisation measurement. In this work, the sample is modelled as a single body connected by a thermal resistance to the cold source.