Effect of Release of Compression on Magnetization of Rocks and Assemblies of Magnetic Minerals

Abstract

IN the preceding communication Nagata and Kinoshita report that the effect of stress on rock magnetization is, in many cases, only partly reversible. It should be pointed out that susceptibility changes reversibly with stress and that the irreversibility is a property of remanent magnetization only. But any process by which a magnetic material acquires remanence must be irreversible in the thermodynamic sense. The vital question raised by Nagata and Kinoshita is: does this irreversibility invalidate simple calculations of the seismomagnetic effect which assume the established reversible piezomagnetic effect ? On the evidence available at present I consider that it does not.