SINGLE-DOMAIN THEORY FOR REVERSIBLE EFFECT OF SMALL UNIAXIAL STRESS UPON REMANENT MAGNETIZATION OF ROCK

Theoretical expressions are derived (using rigorous energy-minimization but ignoring thermal activation) for reversible change in remanence parallel to the stress axis for samples containing single-domain grains of a ferromagnet with cubic magnetocrystalline anistorpy and anisotropic magnetostriction. The grains are assumed to be non-interacting and randomly oriented spheres or ellipsoids of revolution elongated along certain directions. Also, approximate expressions are given for samples containing multidomain grains with very strongly pinned walls. Thermal (or chemical), anhysteretic, and saturation remanence are discussed. For remanence change perpendicular to the stress axis, one expects - one-half the above expressions for change parallel to the stress axis, which is easily proven for thermal remanence. The expressions make predictions for the decrease in thermal remanence along a 100 bar compression axis for magnetite-bearing rock. Refs.