Journal of Geophysical Research Atmospheres · 1986 · 231 citations · 63 references
Natural SciencesMaterials EngineeringMaterials ScienceElectromagnetismMagnetic MaterialsMaterials CharacterizationMagnetic CharacterizationMagnetic Properties Of SolidsMagnetic SusceptibilityMagnetism In SolidsMagnetization ProcessesRemanent MagnetizationGrain Size Effects On MagnetizationHysteresisHysteresis BehaviorHysteresis PropertiesMagnetic Hysteresis ParametersMagnetic Materials CharacterizationMagnetiteMagnetite Remanence
The study reports room‑temperature measurements of magnetic hysteresis parameters for single‑crystal magnetite cubes of 0.037–0.22 μm in size. Measurements included initial susceptibility, second Rayleigh coefficient, coercive and remanent coercive forces, and the remanence‑to‑induced magnetization ratio for four samples. The data show that while initial susceptibility and coercive force vary only weakly with particle size, coercive force and remanence ratio exhibit strong size dependence (∝ d^−0.55 and d^−0.75) over 0.076–0.22 μm, with perfect crystals displaying 2–5 × lower values than pulverized grains, and these behaviors are inconsistent with data for >1 μm grains and can be partially explained by metastable single‑domain particles, rotatable domain‑wall moments, or defect‑limited domain‑wall displacements, with only reversible domain‑wall motion accounting for the initial susceptibility.
This paper reports room temperature measurements of initial susceptibility χ 0 , second Rayleigh coefficient B, coercive force H c , remanent coercive force H R , and the ratio J rs /J s of near‐saturation remanent and induced magnetizations for four samples containing single‐crystal magnetite cubes with mean sizes of 0.037, 0.076, 0.10, and 0.22 μm. While χ o and H c have weak dependences on particle size d, H c and J rs vary strongly with size, as d −0.55 and d −0.75 , respectively, over the 0.076–0.22 μm range. These hysteresis properties and their size dependences are incompatible with data for >l‐μm crushed and annealed magnetite grains. Nearly perfect unstrained crystals tend to have H c and J rs values 2–5 times smaller than those of pulverized grains of nominally the same size. Magnitudes and size dependences of H c and J rs for >0.06‐μm magnetites are approximately, although not perfectly, accounted for by (1) metastable single‐domain (SD) particles, (2) rotatable SD‐like domain wall (DW) moments, or (3) DW displacements impeded by crystal defects and limited by self‐demagnetization. Only reversible DW displacements (or possibly domain rotations) opposed by self−demagnetization can explain the initial susceptibility data, however.
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Some theoretical aspects of rock-magnetism
Louis Néel · Advances In Physics · 1955 · 1.1K citations · Full text