Piezo-Remanent Magnetism in Rock and Its Field Evidence

Irreversible changes of the remanent magnetization of fine grains of ferromagnetics under uniaxial compression have been experimentally examined in a systematic way. The compression of a sample in a magnetic field results in a remanent magnetization which is greater than that obtained without compression in the same field. The pressure remanent magnetization PRM produced by removing uniaxial compression in a magnetic field increases with increasing compressional stress. The dependence of the PRM of a fine grain assemblage of titanomagnetite upon pressure P and a magnetic field Hex can be expressed by af(p)Hex, where f(p) increases monotonically with respect to pressure, reaching some limitting value at pressures higher than 2 kb, and a is a numerical constant systematically dependent on grain size. The ratio of PRM/IRM in a weak magnetic field for homogeneous bulk specimens with grain size larger than about 0.1 mm varies from 1 to 5, whereas specimens containing fine grains with diameters less than 0.1 microns have ratios of 20 to 40. A similar grain size dependence is found for Cu-Co superprecipitates containing homogeneously dispersed ferromagnetic fine grains in a non-ferromagnetic matrix. Stability of the PRM of a fine grain assembalge of titanomagnetite has been examined through ac field demagnetization. The decay of PRM with respect to increasing peak intensity of an ac field resembles that of IRM rather than that of ARM.The intensity of various types of remanent magnetization, such as TRM, IRM and ARM, decreases irreversibly as the specimen is compressed uniaxially in a non-magnetic space. The observed hyperbolic decay of remanent magnetization with increasing compressional stress can be accounted for by a PRM induced by the demagnetizing field of the specimen itself in a reverse sense to the initial remanent magnetization. It is shown that the PRM vector deviates from the direction of an external magnetic field toward a plane perpendicular to the compressional axis when the magnetic field is not parallel or perpendicular to the axis of compression. The maximum deflection angle is calculated to be 10 degrees and occurs when the angle between the magnetic field and the compressional axis is about 45 degrees.The mechanism of acquisition of PRM is briefly discussed. A more detailed discussion of the problem will be given in a future paper.

Section: -1 Prm Of Titanomagnetitessupporting

confidence: 73%

Section: -1 Pressure Demagnetization Of Remanent Magnetizationmentioning

confidence: 56%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Studies on Piezo-Magnetization (III)

Kinoshita¹

1968

“…The effect has been studied systematically by Domen (1962) using assemblages grains of natural magnetite. Similar experimental studies on the irreversible change magnetization of metals and alloys due to an external axial stress were carried out as as 1890, by Nagaoka (1889) on pure nickel wires, by Honda and Terada (1907) on steel wires and by Carmichael and Fuller (1967) on pure nickel rods.…”

Section: Introductionmentioning

confidence: 99%

Studies on Piezo-Magnetization (IV)

Kinoshita

1969

Experimental studies on PRM (Kinoshita 1968) are discussed theoreticall asis ofimental studies on PRM (Kinoshita 1968) are discussed theoretically basis, 1965) in which irreversible rotation of the spontaneous magnetization vector individual ferromagnetic fine grains of the specimen at a certain value of external compre stress is taken into account to explain the acquis PRM.It is assumed that the external stress exer specimen is a purely uniaxial compressional stress whose intensity varies from grain to grain, in the from of distribution. PRM versus pressure and PRM versus external magnetic field are qualitatively well explained by the single domai.

“…In many of their experiments, uniaxial stress was applied to rock specimens cooling from high temperatures in the earth's magnetic field, and the TRM of these specimens was compared with TRM of those cooled in the earth's field without stress. Domen (1962) studied the irreversible change in remanent magnetization caused by the application of compressive stress in the presence of the geomagnetic field, using an assemblage of powdered natural magnetite. Nagata and Kinoshita (1965) examined the problem more thoroughly for the purpose of applying the results to seismomagnetic effects.…”

Section: Introductionmentioning

confidence: 99%

Stability of Remanent Magnetization of Rocks under Compression-Its Relation to the Grain Size of Rock-forming Ferromagnetic Minerals

OHNAKA

1969

Stress stability of the remanent magnetization of basalt under compression was experimentally tested. It was also examined, using a thick lava of basalt, whether the effect of compressive stress on remanent magnetization depends upon grain size of rock-forming ferromagnetic minerals. Intensity of IRM of the rocks shows an irreversible and remarkable reduction under axial compression. TRM and NRM decrease gradually as axial force is increased. Change of remanent magnetizations with respect to pressure is well expressed in a hyperbolic form: M(P)=Mo/(1+/Br.P), in the same manner as that of the initial magnetic susceptibility of volcanic rocks. TRM is more stable than IRM against pressure.For IRM, the stronger the applied magnetic field, the more stable the intensity and direction of remanent magnetization become with respect to pressure. It was found that the magnetically effective grain size of ferromagnetic minerals controls the stress stability of NRM as well as the intensities of TRM, the coercive force and the initial magnetic susceptibility.