The Limiting Sensitivity of an Alternating-Current Method of Measuring Small Magnetic Moments

Abstract

A method of measuring the moment of small magnetic dipoles is described. The dipole to be measured is rotated inside of a fixed coil, and the voltage induced in the coil is measured by means of an alternating-current amplifier. The limiting sensitivity is computed from the calculated signal-voltage and the thermal agitation in the input circuit. In the practical application the theoretical sensitivity is approximately obtained and moments of 3×10−7 c.g.s. unit can be detected and with a specimen 1.5 cm on a side 8×10−8 c.g.s. unit/cc can be detected. The method has been applied to the measurement of the polarization in sedimentary deposits.