Determining magnetic anisotropy of rocks with a spinner magnetometer giving in-phase and quadrature data output

A relationship is developed between magnetic anisotropy measurements and the total magnetic susceptibility tensor, in terms of the in-phase and quadrature output components of a two-component spinner magnetometer. Calibration procedures for both signal phase and magnitude are discussed, with reference to remanent magnetization measurement, in terms of a wire loop and mu-metal plate, whose induced magnetizations and anisotropy can be theoretically calculated. The importance of careful reference signal phase adjustment is noted, and the effect on the output amplitude for small systematic errors in simple position and reference phase angle is considered. An average uncertainty in the anisotropy output magnitude is thought to be in the range of 1% to 5%.