AC susceptibility measurement in high frequency region up to 10 kHz using a SQUID magnetometer MPMS

Abstract

We performed AC magnetic susceptibility measurement for high frequency (f) range, based on a superconducting quantum interference device (SQUID) magnetometer, MPMS (Quantum Design Inc.). Original system of MPMS uses an A/D converter with 12 bit or 16 bit, and there the frequency of AC field is limited to less than 1 kHz by a software. In the present system, we transformed an analog signal of SQUID output to a digital one via an A/D converter with 24 bit, and generated AC field by a signal generator outside MPMS. The maximum f was enlarged from 1 kHz to 10 kHz. However, it has been confirmed that amplitude of AC field (HAC), at which the rf-SQUID works as a current/voltage transformer, decreases with increasing f. The value of HAC was restricted below 0.02 Oe at f = 10 kHz. The performance of the present system has been confirmed via the measurements of a paramagnetic material Dy 2O3 and a rare-earth ferromagnet Ho. The normalization constant for the magnitude of the SQUID output, to calibrate the effect of eddy current, is presented as a function of frequency. © 2010 IOP Publishing Ltd.