Use of a phase-sensitive detector for measuring magnetic hysteresis loops

A method for magnetic hysteresis loop measurement on small samples of high Tc superconductors is described, applicable to other types of magnetic materials as well. It is based on an unusual working regime of the phase-sensitive detector with a square wave mixer signal and controllable reference phase setting. The main advantages of the method are its sensitivity and the possibility of measuring in a wide frequency range. A drawback of the method is that it is fully correct only in the case of a symmetrical hysteresis loop.