A high-resolution, SQUID-based vibrating coil susceptometer

A superconducting quantum interference device (SQUID) plays an important role in the development of ultrasensitive electric and magnetic measurement systems. SQUID instrumentation offers diversified applications with its ability to make measurements where other methodologies could not be applied. A high sensitivity magnetic measurement technique to measure the magnetic susceptibility of extremely small volume samples using a SQUID vibrating coil magnetometer (SVCM) has been developed. In this setup, position differentiating detection (PDD) of magnetic flux from the sample has been coupled with the SQUID magnetometer. The sensitivity of the setup depends on the vibrating amplitude of the pick-up coil. The pick-up coil of the SVCM has been steadily vibrated with a maximum amplitude of 75 µm close to the sample at the resonant frequency using bimorph piezoelectric bender type actuators. An equivalent circuit model for the piezoelectric actuator has been constructed, and its resonance frequency has also been cross-checked by simulation software. The vibration of actuators for a wide range of temperatures (4.2 K–300 K) has been controlled by a negative feedback circuit. The detailed design, construction and performance of the SVCM have been described.