An Experimental Investigation of the Magnetic Properties of Crystalline Powders with Reference to the Dependence of Susceptibility on Crystal Size

Citation

Gregory, Carter Holt (1935) An Experimental Investigation of the Magnetic Properties of Crystalline Powders with Reference to the Dependence of Susceptibility on Crystal Size. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/s2rf-yj24. https://resolver.caltech.edu/CaltechTHESIS:10302024-180305992

Abstract

A method is described by means of which it is possible to measure the magnetic susceptibility of suspensions of finely divided graphite as single crystals. According to this method, the principal susceptibilities of graphite are

X_┴ 0.44 x 10^-6

X₁₁ 13.35 x 10^-6

As reported by other observers, the mean susceptibility is found to decrease with decreasing particle size. The decrease of susceptibility is accompanied by a proportionate decrease in the magnetic anisotropy X₁₁/X_┴. At low temperatures, the phenomenon remains qualitatively unchanged; no displacement of the critical size is observed.

Measurements on paramagnetic MnO₂ show no variation of susceptibility with particle size. A slight decrease of susceptibility with decreasing particle size is found in the case of paramagnetic Cr₂O₃, although here the effect may be spurious. Experiments of a provisional nature would indicate that the susceptibilities of substances whose magnetic properties are intermediate between those of paramagnetics and ferromagnetics decrease rapidly with decreasing particle size when a critical diameter of particle of approximately 3µ reached.

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