Single-domain theory for the reversible effect of small uniaxial stress upon the initial magnetic susceptibility of rock

1976 ◽  
Vol 13 (9) ◽  
pp. 1186-1200 ◽  
Author(s):  
J. P. Hodych
Keyword(s):  
Magnetic Susceptibility ◽  
Coercive Force ◽  
Thermal Activation ◽  
Magnetocrystalline Anisotropy ◽  
Uniaxial Stress ◽  
Single Domain ◽  
Stress Axis ◽  
Compression Axis ◽  
Initial Magnetic Susceptibility ◽  
Approximate Expressions

The phenomenon of small uniaxial stress changing the magnetic susceptibility of rock is of current interest as a possible aid in earthquake forecasting.In this paper, theoretical expressions are derived (using rigorous energy-minimization, but ignoring thermal activation) for reversible susceptibility change parallel to the stress axis for samples containing single-domain grains of a ferromagnet with cubic magnetocrystalline anisotropy (K1, positive or negative) and anisotropic magnetostriction. The grains are assumed to be non-interacting and randomly oriented spheres or ellipsoids of revolution elongated along [Formula: see text], [Formula: see text] or [Formula: see text]. Also, approximate expressions are given for samples containing multidomain grains with very strongly pinned walls.For susceptibility change perpendicular to the stress axis, one expects −½ the above expressions, which is proven for spherical single-domain grains with isotropic magnetostriction using a magnetometer analogy.The expressions predict that for magnetite-bearing rock the decrease in susceptibility along a 100 bar compression axis should be 4.7% for spherical single-domain grains (coercive force ~100 Oe), 1.6% for 1.4 to 1 elongation along [Formula: see text] (coercive force ~500 Oe), and 0.6% for great elongation along [Formula: see text]. The decrease for equidimensional multidomain grains with strongly pinned walls (coercive force ~100 Oe) should be ~1.2%—less at smaller coercive force according to some theoreticians, possibly more according to my experiments.

Single-domain theory for the reversible effect of small uniaxial stress upon the remanent magnetization of rock

1977 ◽  
Vol 14 (9) ◽  
pp. 2047-2061 ◽  
Author(s):  
J. P. Hodych
Keyword(s):  
Remanent Magnetization ◽  
Thermal Activation ◽  
Magnetocrystalline Anisotropy ◽  
Uniaxial Stress ◽  
Titanium Content ◽  
Single Domain ◽  
Stress Axis ◽  
Compression Axis ◽  
Saturation Remanence ◽  
Approximate Expressions

This paper on small uniaxial stress changing the remanent magnetization of rock is a companion to my previous paper on stress changing susceptibility, both phenomena being of current interest in attempts at earthquake forecasting.Theoretical expressions are derived (using rigorous energy-minimization but ignoring thermal activation) for reversible change in remanence parallel to the stress axis for samples containing single-domain grains of a ferromagnet with cubic magnetocrystalline anisotropy (K1 positive or negative) and anisotropic magnetostriction. The grains are assumed to be non-interacting and randomly oriented spheres or ellipsoids of revolution elongated along [Formula: see text], [Formula: see text], or [Formula: see text]. Also, approximate expressions are given for samples containing multidomain grains with very strongly pinned walls. Thermal (or chemical), anhysteretic, and saturation remanence are discussed.For remanence change perpendicular to the stress axis, one expects −1/2 the above expressions for change parallel to the stress axis, which is easily proven for thermal remanence.The expressions predict that for magnetite-bearing rock the decrease in thermal remanence along a 100 bar (1 × 104 kPa) compression axis should be 0.76% for spherical single-domain grains, 0.27% for 1.4 to 1 elongation along [Formula: see text], and 0.09% for great elongation along [Formula: see text]. The decrease for equidimensional multidomain grains with strongly-pinned walls should be ~0.38%. These are all much smaller than the corresponding estimates for susceptibility, but both remanence and susceptibility decreases should become larger and more comparable as titanium content increases.

Application of Micromagnetic Models for Barium Ferrite Magnets

2015 ◽  
Vol 820 ◽  
pp. 199-204 ◽  
Author(s):  
Marcos Flavio de Campos ◽  
Fernanda A. Sampaio da Silva
Keyword(s):  
Particle Size ◽  
Grain Size ◽  
Coercive Force ◽  
Total Energy ◽  
Barium Ferrite ◽  
Magnetocrystalline Anisotropy ◽  
Single Domain ◽  
Square Root ◽  
Single Domain Particle ◽  
Magnetostatic Energy

The applicability of micromagnetics for phases with high magnetocrystalline anisotropy as barium ferrite Ba2Fe12O19and Nd2Fe14B is discussed. The Stoner-Wohlfarth model is very suitable for such phases, and also for PtFe and PtCo. It was discussed how to take into account the total energy of the system for grain size above the single domain particle size. For this situation of large grain size, the net magnetostatic energy of the system cannot be neglected. From energy considerations, it follows that the coercive force should decrease with the inverse of the square root of the grain size.

Effect of magnetocrystalline anisotropy in single-domain polycrystalline cobalt islands

1995 ◽  
Vol 31 (6) ◽  
pp. 3805-3807 ◽  
Author(s):  
R.M.H. New ◽  
R.F.W. Pease ◽  
R.L. White
Keyword(s):  
Magnetocrystalline Anisotropy ◽  
Single Domain

The initial magnetic susceptibility of polydisperse ferrofluids: A comparison between experiment and theory over a wide range of concentration

2016 ◽  
Vol 145 (8) ◽  
pp. 084909 ◽  
Author(s):  
Anna Y. Solovyova ◽  
Olga A. Goldina ◽  
Alexey O. Ivanov ◽  
Aleksandr V. Lebedev ◽  
Ekaterina A. Elfimova
Keyword(s):  
Magnetic Susceptibility ◽  
Wide Range ◽  
Initial Magnetic Susceptibility

A.C. initial magnetic susceptibility and spin reorientation transitions in (ErxR1−x)2Fe14B magnets (R=Nd and Dy)

1989 ◽  
Vol 69 (2) ◽  
pp. 131-136 ◽  
Author(s):  
M.R. Ibarra ◽  
C. Marquina ◽  
P.A. Algarabel ◽  
J.I. Arnaudas ◽  
A. del Moral
Keyword(s):  
Magnetic Susceptibility ◽  
Spin Reorientation ◽  
Initial Magnetic Susceptibility

scholarly journals Effect of Mechanical Stresses on the Coercive Force of the Heterophase Non-Interacting Nanoparticles

2012 ◽  
Vol 472-475 ◽  
pp. 2199-2202 ◽  
Author(s):  
Leonid Afremov ◽  
Yury Kirienko
Keyword(s):  
Theoretical Analysis ◽  
Coercive Force ◽  
Saturation Magnetization ◽  
Exchange Interaction ◽  
Cobalt Ferrite ◽  
Uniaxial Stress ◽  
Mechanical Stresses ◽  
Residual Saturation

The theoretical analysis of the effect of uniaxial stress on the magnetization of the system of noninteracting nanoparticles is done by an example of heterophase particles of maghemite, epitaxially coated with cobalt ferrite. It is shown that stretching leads to a decrease in the coercive force Hc, and compression leads to its growth. The residual saturation magnetization Irs of nanoparticles does not change. With increasing of interfacial exchange interaction, coercive force varies nonmonotonically.

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