Differential method for sample holder background subtraction in superconducting quantum interference device (SQUID) magnetometry

A new differential measuring technique for high sensitivity magnetic moment measurements is presented as an application to the Quantum Design Magnetic Property Measurement Systems (MPMS) Superconducting Quantum Interference Device (SQUID). The system is particularly suitable for measurements of samples having magnetic signal of the same order of magnitude of the sample holder, like materials with weak magnetic moment contained in quartz diamagnetic capsule and thin magnetic films. For such kind of samples, the standard measurement procedures currently employed to subtract the holder background are very sensitive to misalignment errors, on the contrary the proposed new technique is completely insensitive with respect to misalignment inaccuracy. SQUID background drift and dc instrumental offset are automatically managed as well. The working principle is first analyzed by means of theoretical analysis and numerical simulations, showing its superiority with respect to standard measurement procedures with regard to misalignment effects. Then, a test case regarding a sample of known properties is developed, showing that the results obtained by this new technique and by the standard measurement procedures are in excellent agreement, confirming therefore the reliability of the method.