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Rock Magnetism, first published in 1997, is a comprehensive treatment of fine particle magnetism and the magnetic properties of rocks. Starting from atomic magnetism and magnetostatic principles, the authors explain why domains and micromagnetic structures form in ferromagnetic crystals and how these lead to magnetic memory in the form of thermal, chemical and other remanent magnetizations. The phenomenal stability of these magnetizations, providing a record of plate tectonic motions over millions of years, is explained by thermal activation theory. One chapter is devoted to practical tests of domain state and paleomagnetic stability; another deals with pseudo-single-domain magnetism. The final four chapters place magnetism in the context of igneous, sedimentary, metamorphic, and extraterrestrial rocks. This book will be of great value to graduate students and researchers in geophysics and geology, particularly in paleomagnetism and rock magnetism, as well as physicists and electrical engineers interested in fine-particle magnetism and magnetic recording.

At the Verwey transition (Tv≈110–120 K), magnetite transforms from monoclinic to cubic spinel structure. It has long been believed that magnetic remanence and susceptibility would change markedly at Tv in the case of coarse grains but only slightly or inappreciably in the case of fine (<1 µm) grains. We find on the contrary that remanence changes at Tv by 50–80% in both large and small crystals, if they are stoichiometric. However, minor surface oxidation suppresses the transition, and the fact that fine grains oxidize more readily leads to an apparent size dependence. Our experiments used submicron magnetite cubes with mean sizes of 0.037, 0.076, 0.10 and 0.22 µm which were initially non‐stoichiometric (oxidation parameter z from 0.2–0.7). A saturation isothermal remanent magnetization (SIRM) given in a 2.5 T field at 5 K decreased steadily during zero‐field warming to 300 K with little or no indication of the Verwey transition. After the oxidized surface of each crystal was reduced to stoichiometric magnetite, the SIRM decreased sharply during warming by 50–80% around 110 K. The change in SIRM for the 0.22 µm grains was almost identical to that measured for a 1.5 mm natural magnetite crystal. Thus a 1012 change in particle volume does not materially affect the remanence transition at Tv but oxidation to z=0.3 essentially suppresses the transition. The effect of the degree of oxidation on Tv provides a sensitive test for maghemitization in soils, sediments and rocks.