Magnetite

About: Magnetite is a research topic. Over the lifetime, 10277 publications have been published within this topic receiving 278071 citations.

Polystyrene-Grafted Magnetite Nanoparticles Prepared through Surface-Initiated Nitroxyl-Mediated Radical Polymerization

Abstract: Surface-modified magnetite (Fe3O4) nanoparticles (d = 10 nm) was prepared by direct polymerization of styrene on their surface. With use of nitroxyl-mediated initiator for radical polymerization with the phosphonic acid group, magnetite particles with a controlled polystyrene graft layer on the surface were successfully prepared. The surface-modified magnetite was dispersed in good solvents for polystyrene such as chloroform, toluene, ethyl acetate, and benzene.

Evidence for a Magnetite-Based Navigational “Map” in Birds

Abstract: * Present address: University of Technology, Sydney, Department of Environmental Biology and Horticulture, P.O. Box 123, Broadway, NSW 2007, Australia Birds may use the magnetic field in two ways: as a compass for locating directions and as a component of the navigational “map” for determining position. Due to the different types of magnetic information involved, two different systems of magnetoreception have been proposed, and it has been speculated that one of these receptors is based on biogenic magnetite. Treatments with a brief, high-intensity magnetic pulse designed to alter the magnetization of magnetite particles found in the birds’ heads indeed affected orientation behavior. This supports the hypothesis that a magnetitebased receptor provides orientational information. However, since all birds tested previously had homing and/or migratory experience, it could not be decided whether the pulse has affected their “map” or their compass. Here we present data obtained on inexperienced juvenile birds which strongly suggest that the “map” rather than the compass is based on magnetite. Ever since magnetite crystals of biogenic origin have been found in organisms [1, 2], it has been speculated that these particles are involved in magnetoreception [3]. Many birds show accumulations of magnetite in the ethmoid region [4, 5], which is consistent with the possibility of a magnetite-based sensor. Behavioral studies support this hypothesis. Subjecting birds to a brief high-intensity Naturwissenschaften 84, 26–28 (1997) © Springer-Verlag 1997

Occurrence of secondary magnetite within biodegraded oil

Abstract: Samples of solid bitumen from the Thornton Quarry (Illinois) and the Cynthia Quarry (Mississippi) were found to be strongly magnetic and to have rock magnetic properties suggesting that the magnetizable grains present are magnetite. Studies of magnetic isolates revealed that magnetite is present primarily as spherical crystal aggregates that appear identical to magnetite spherules isolated from re-magnetized Paleozoic carbonate units from other localities. Organic geochemical analyses of the solid bitumen suggest an origin by microbial attack on what once was liquid crude oil. The occurrence of secondary magnetite as inclusions within solid bitumen suggests a relationship between crude oil biodegradation and development of that mineral in our samples. We infer that secondary magnetite in other geologic environments may be related to the presence of hydrocarbons. The discovery of a natural association of secondary magnetite and hydrocarbons has important implications for paleomagnetism and for petroleum exploration.

Speed limit of the insulator-metal transition in magnetite

Abstract: As the oldest known magnetic material, magnetite (Fe3O4) has fascinated mankind for millennia. As the first oxide in which a relationship between electrical conductivity and fluctuating/localized electronic order was shown, magnetite represents a model system for understanding correlated oxides in general. Nevertheless, the exact mechanism of the insulator-metal, or Verwey, transition has long remained inaccessible. Recently, three-Fe-site lattice distortions called trimerons were identified as the characteristic building blocks of the low-temperature insulating electronically ordered phase. Here we investigate the Verwey transition with pump-probe X-ray diffraction and optical reflectivity techniques, and show how trimerons become mobile across the insulator-metal transition. We find this to be a two-step process. After an initial 300 fs destruction of individual trimerons, phase separation occurs on a 1.5±0.2 ps timescale to yield residual insulating and metallic regions. This work establishes the speed limit for switching in future oxide electronics.