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AC Susceptibility Measurement

AC susceptibility measurements yield information about magnetization dynamics, which are not obtained from DC measurements, where the sample moment is constant during the measurement time. A modulation coil is used to generate an AC magnetic field, leading to a time dependent magnetic moment in the sample. There are two pick-up coils in the susceptometer. One pick-up coil contains the sample and a current will be induced by the field of the time-dependent moment. The other pick-up coil is wound in the opposite direction in order to cancel the background signal.

The winding machine is shown above and consists of two step motors. A two-channel square wave generator sends signals to the controller to drive the step motors. One step motor controls the displacement and the other rotates around the main axis. Since the wire of the coil has a diameter of tens of microns, a microscope is used when operating the system.