Versatile SQUID Susceptometer With Multiple Measurement Modes

We present a state of the art SQUID-based susceptometer which supports lock-in style vibrating sample magnetometer (VSM) measurements as well as traditional dc scans using a single motion control and detection circuit for both measurements. The dc scan fits the measured SQUID response as function of position to an expected response waveform and includes algorithm enhancements for better rejection of external magnetic signals. The VSM-style measurement uses a novel approach for its data acquisition, which is designed to minimize cross talk between the mechanical movement of the sample and the measured signal. In addition, the superconducting gradiometer of the detection circuit is optimized for best signal-to-noise performance in both types of measurements, achieving sensitivity in the range of 10-8 emu at fields up to 7 Tesla. This dual measurement capability allows a single instrument to measure a wide variety of samples by choosing the method most fitting to constraints imposed by the sample, e.g., limiting thermal and magnetic field variations or reducing forces the sample is exposed to during the measurement. Special consideration is given to a detailed analysis of the advantages of the different measurement methods, the influence of measurement parameters on the reported results, as well as the effect of sample properties and sample geometry on the reported moment.