Development of high field SQUID magnetometer for magnetization studies up to 7 T and temperatures in the range from 4.2 to 300 K

Abstract

We present the design, fabrication, integration, testing, and calibration of a high field superconducting quantum interference device (SQUID) magnetometer. The system is based on dc SQUID sensor with flux locked loop readout electronics. The design is modular and all the subsystems have been fabricated in the form of separate modules in order to simplify the assembly and for ease of maintenance. A novel feature of the system is that the current induced in the pickup loop is distributed as inputs to two different SQUID sensors with different strengths of coupling in order to improve the dynamic range of the system. The SQUID magnetometer has been calibrated with yttrium iron garnet (YIG) sphere as a standard reference material. The calibration factor was determined by fitting the measured flux profile of the YIG sphere to that expected for a point dipole. Gd₂O₃was also used as another reference material for the calibration and the effective magnetic moment of the Gd³⁺ could be evaluated from the temperature dependent magnetization measurements. The sensitivity of the system has been estimated to be about 10⁻⁷ emu at low magnetic fields and about 10⁻⁵ emu at high magnetic fields ~7 T.