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A vibrating sample magnetometer or VSM is a scientific instrument that measures magnetic properties. Simon Foner at MIT Lincoln Laboratory invented VSM in 1955 and reported it in 1959. A sample is first magnetized in a uniform magnetic field. It is then sinusoidally vibrated, typically through the use of a piezoelectric material. Commercial systems use linear actuators of some form. Historically these systems were developed using modified audio speakers, though this approach was dropped due to the interference through the produced in-phase magnetic noise, as the magnetic flux through a nearby pickup coil varies sinusoidally. The induced voltage in the pickup coil is proportional to the sample's magnetic moment, but does not depend on the strength of the applied magnetic field. In a typical setup, the induced voltage is measured with a lock-in amplifier using the piezoelectric signal as a frequency reference. It is also possible to record the hysteresis curve of a material by sweeping the magnetic field.
The idea of vibrating sample came from D. O. Smith's vibrating coil magnetometer.