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/cm
2. 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 as
JR(
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
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