Magnetic Viscosity of Magnetite

Abstract

Magnetic viscosity of ensemble of medium-sized grains of natural magnetites was examined at various temperatures.It was found that magnetic viscosity coefficient S, defined as I-I0=S(Q+logt) where I and I0 are intensity of magnetization at time t and t=0, is proportional to external magnetic field, and S is a linear function of temperature, except at temperatures close to the Curie point seems also that S tends to a finite value according as grain size tends to the order of a single domain.Further, the half life time for sedimentary rocks, in which directions of grain magnetization are scattered, with reduction factor w, is about 1010 years for w=1/5.These results may show that remanent magnetization of igneous and sedimentary rocks have been stable against thermal viscosity during a geologically long time.

Low-temperature viscous magnetization of multidomain magnetite: Evidence for disaccommodation contribution

“…E(2 mm) displays only one peak just below T V . Above T V , in all three samples S A and S D are greatly reduced, but increase gradually on warming to 300 K. Samples W(11 μm) and H(23 μm) display a broad peak centered at 160-200 K. The large drop in viscosity rate on warming through T V is greater than that reported in other studies for SD [5] and MD [22] magnetite. (Fig.…”

“…Shimizu [22] also found that the viscosity rate was also enhanced below the Verwey transition, but this time for MD magnetite, although this phenomenon was not discussed in the text. On comparison of the low-temperature disaccommodation spectra with the limited published low-temperature viscosity data, then there is reason to believe that disaccommodation will contribute significantly to the magnetic viscosity below T V, and it is this issue that this investigation addresses.…”

The Nature of Secondary Natural Magnetizations in Some Igneous and Baked Rocks

“…Theories of viscous magnetization in single domain magnetic grains were developed by Neel (1949A) and Brown (1959) and in multidomain grains by Neel (1949B), Stacey (1959), and Averyanov (1967. Laboratory experiments have substantiated these theories quite well (Barbier 1954, Shimizu 1960, Le Borgne 1960, Plessard 1961, Janovsky and Sholpo 1962.…”

Study on the Stability of VRM with Low-Temperature Treatment and Some Magnetic Characteristics of Granite

“…This may be explained by the experimental fact (Shimizu, 1960) that the viscosity magnetic field constant Sv of magnetite becomes maximum at about 200C.…”

“…6 Shows variation of magnetic viscosity field constant Sv as a function of absolute temperature (after Shimizu, 1960 (ii) VRM of magnetite grains (grain size J50u) produced with a longer application of a magnetic field becomes more resistant to the low-temperature demagnetization.…”