Highly sensitive microcomputer-controlled AC magnetometer with a phase locked data acquisition system

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Abstract
A highly sensitive magnetometer for AC measurements in applied fields of up to 3*105 A m-1 is described. It is based on a mains-powered solenoid, and a high resolution signal averaging system capable of analysing extremely small signals down to the order of electronic noise (about 1 mu V). The high density of data points allowed by the system demands a personal computer acting as control unit for data acquisition (based on linear summation averaging) and data handling. The AC magnetometer was employed to record the magnetisation curves, M against H, of ferromagnetic samples having small magnetically effective cross sections, and to determine their AC magnetic properties, (saturation magnetisation, remanence, coercivity, susceptibility) in the temperature range down to 4.2K.