The acquisition of piezo-remanent magnetization (PRM) of igneous rocks under uniaxial compression is experimentally studied. It has been found that the rate of acquisition of PRM is several times as large as that of assemblages of magnetic minerals. This is in remarkable contrast to another observed fact that the rate of decrease of magnetic susceptibility owing to an increase of uniaxial compression in rocks is about one order smaller than that in magnetic minerals.
The rate of acquisition of PRM is larger in a smaller magnetic field than in a larger magnetic field, and it is larger for rock samples which are magnetically harder, having a larger value of magnetic coercive force and a slower rate of decrease by AC-demagnetization.
It is qualitatively shown that all these experimental results can be consistently explained based on a simple model of configuration of magnetic domains of magnetic minerals under the effect of inverse mangetostriction.