Notes on Piezo-remanent Magnetization of Igneous Rocks II

Abstract

Various characteristics of piezo-remanent magnetization of igneous rocks are experimentally demonstrated in small magnetic fields, H=0-10Oe., and under uniaxial compression comparable to the earth's crust stress, 0-100kg/cm2. The main characteristics observed are as follows:(a) “After-effect” of uniaxial compression: JR(P+P0H+H0).After a rock sample is uniaxially compressed in a non-magnetic space by a pressure P larger than a certain critical value (Pc), its IRM, JR(P+P0H+H0), becomes larger than the ordinary IRM, JR(H+H0), without such a pressure treatment. This after-effect of pressure takes place in both cases of P//H and P⊥H.Here [d/dPJR(P+P0H+H0)]H=const>0 for P>Pc.(b) “Pressure demagnetization” effect: JR(H+H0P+P0).After uniaxially compressing a rock sample having IRM, JR(H+H0), in a non-magnetic space, the residual magnetization, JR(H+H0P+P0), becomes appreciably smaller than the original intensity of JR(H+H0) in both cases of P//H and P⊥H.Here [d/dPJR(H+H0P+P0)]H=const<0, and [d2/dP2JR(H+H0P+P0)]H=const>0.(c) “Non-commutativity” of P and H.An inequality relationship expressed asJR(H+P+P0H0)≥JR(P+H+P0H0)>JR(H+P+H0P0)≥JR(P+H+H0P0)holds for all samples. In a magnetic field larger than a certain critical value, H*, JR(P+H+H0P0)<JR(H+H0), but in H<H* JR(P+H+H0P0)>JR(H+H0).JR(H+P+P0H0) and JR(P+H+P0H0) are always larger than JR(H+H0). The above argument holds in both cases of P//H and P⊥H.(d) A linear dependence of PRM on H.JR(H+P+P0H0) is defined as piezo-remanent magnetization. In a range of small magnetic fields, JR(H+P+P0H0)∞H for P=constant, though JR(H+H0)∞H2 in the