Lamellar magnetism: effects of interface versus exchange interactions of nanosca

2020-03-06 05:36:31

spin layers magnetization hematite ilmenite

责任者: McEnroe, S.A.;Harrison, R.J.;Jackson, M.J.;Hirt, A.M.;Robinson, P.;Langenhorst, F.;Heidelbach, F.;Kasama, T.;Putnis, A.;Brown, L.L.;Golla-Schindler, U 单位: Geol. Survey of Norway, Trondheim, Norway 来源出处: Journal of Physics: Conference Series(J. Phys., Conf. Ser. (UK)),2005//,17(1):154-67 摘要: We have examined finely exsolved oxides of the hematite-ilmenite solid-solution series found in slowly cooled middle Proterozoic igneous and metamorphic rocks. These oxides impart unusually strong and stable remanent magnetization. Transmission electron microscopy (TEM) analysis shows multiple generations of ilmenite and hematite exsolution lamellae, with lamellar thicknesses ranging from millimeters to 1-2 nanometers. Rock-magnetic experiments suggest that the remanence is thermally locked to the antiferromagnetism of the hematite component of the intergrowths, yet is stronger than expected for a canted antiferromagnetic hematite or coexisting paramagnetic Fe-Ti ordered (R 3¯) ilmenite. In alternating field experiments a stable magnetization is observed in these samples to fields of 100 to 120 mT, indicating that the natural remanent magnetization (NRM) is stable over billions of years. This feature has implications for understanding magnetism of deep rocks on Earth, or on planets like Mars that no longer have a magnetic field. Atomic-scale simulations of an (R 3¯) ilmenite lamella in a hematite host, based on empirical cation-cation and spin-spin pair interaction parameters, show that boundary regions of the lamellae are occupied by contact layers with a hybrid composition of Fe ions, intermediate between Fe2+-rich layers in ilmenite and Fe3+-rich layers in hematite. In this paper we review current data and explore further the nature of the interface 关键词: antiferromagnetic materials;canted spin arrangements;exchange interactions (electron);iron compounds;minerals;palaeomagnetism;remanence;rock magnetism;transmission electron microscopy;hematite-ilmenite solid-solution series;finely exsolved oxides;nanoscale exsolutions;exchange interactions;interface interactions;lamellar magnetism;slowly cooled middle Proterozoic igneous rocks;metamorphic rocks;stable remanent magnetization;transmission electron microscopy analysis;exsolution lamellae;lamellar thicknesses;rock-magnetic experiments;antiferromagnetism;antiferromagnetic hematite;paramagnetic Fe-Ti-ordered ilmenite;natural remanent magnetization;Earth;planets;Mars;cation-cation pair interaction;spin-spin pair interaction;contact layers;Fe ions;Fe2+-rich layers;Fe3+-rich layers;100 to 120 mT;Fe2O3-FeTiO3