Detection coil, sensitivity function, and sample geometry effects for vibrating sample magnetometers

Abstract

A general description based on the sensitivity function is presented for the effects of detection coil geometry and sample geometry on the output of a vibrating sample magnetometer (VSM). This function gives the VSM output versus position of a vibrating dipole. Calculations of the sensitivity function for axial and transverse detection coil configurations are presented using exact results and approximations including a spherical harmonic expansion. For axial, thick, rectangular cross-section coils, the design yielding the output with a minimum sensitivity to sample position, sample shape, and sample size is presented. For the transverse geometry the small coil approximation is used. Various designs yielding maximum output and output insensitive to variations of sample geometry are reviewed. The signal-to-noise for various coil configurations is also discussed. Corrections for the VSM output are calculated for ’’large’’ samples with regular geometries (thin rod, circular cylinder, cube, and rectangular parallelepiped). The calculations were verified experimentally for a rod-like sample for different orientations. The effects of applied field homogeneity, sample position errors, and sample support contributions are also discussed. Finally, applications of the analysis to other types of induction and force type magnetometers are discussed briefly.