Project

Discipline

hematite-ilmenite; solid solution; exsolution; decomposition; nanostructure; magnetic ordering; clustering; electron spin resonance; small-angle neutron scattering; transmission electron microscopy; Fe(III) configuration; single crystal; short-range order; nanomineralogy; rock magnetism; material properties; decomposing tendency; nano-scale decomposition; dynamic magnetization; Earth's crust

Lead
Lay summary
Intrinsic decomposing tendency of hematite-ilmenite phases and its effect on static and dynamic magnetic propertiesPD Dr. Andreas U. Gehring, Institute of Geophysics, ETH ZurichThe hematite-ilmenite solid solution series is characterized by an intrinsic decomposing tendency that has been investigated in rock bodies and by thermodynamic modelling. In the present study the effect of nano-scale decomposition on the static and dynamic magnetization is studied.In the 1950s extensive studies on the remanent-magnetization reversal of natural and synthetic minerals of the hematite-ilmenite solid solution series ((1-y) Fe2O3 - y FeTiO3; 0 < y <1) provided a clear demonstration of the theoretical prediction that some mineral phases could be magnetized antiparallel to an applied field. Exchange anisotropy in synthetic hemo-ilmenite solid solution (y = 0.6) revealed that the reversal is caused by the coupling of hard and soft magnetizable phases. The end-members of the hematite-ilmenite series have a corundum structure and are antiferromagnetic with Néel temperatures of 948 K for hematite and of 54 K for ilmenite. In a first approximation, the magnetic ordering temperatures of the solid solutions exhibit a linear increase with increasing mole fraction of Fe2O3. Ilmenite-rich solid solutions (1 > y > 0.5) have a ferrimagnetic ordering which converts into spin glass-like ordering at low temperature.The aim of this project is to investigate the static and dynamic properties of hematite-ilmenite solid solutions by studying powder samples and single crystals. The decomposing tendency of the manufactured samples will be fostered by a combination of annealing and etching. A comparison of structural and magnetic properties of the treated and the starting materials will used to quantify the effects of triggered decomposition on the bulk material.The proposed project provides an insight into the magnetic properties of nano-structures in a well-known binary system which is of relevance for Earth sciences. The information deduced from this system can yield a deeper understanding of the magnetization of the Earth's crust and of weathering and erosion processes that occur on a geological scale. The project will also contribute to the fundamental understanding of magneto-mineralogy on the nano-scale, opening the way to various functional applications in material science.

Direct link to Lay Summary

Last update: 21.02.2013

Number	Title	Start	Funding scheme

The hematite-ilmenite solid solution series ((1-y) ?-Fe2O3 - y FeTiO3; 0 < y <1) is a binary system relevant in physics and the earth sciences. This system has an intrinsic decomposing tendency which has been reported in the context of different rock bodies and confirmed in thermodynamic models. It is proposed to address the effect of nano-scaled decomposition on static and dynamic magnetic properties according to an interdisciplinary approach which combines experimental concepts of rock magnetism and material science. Here various annealing and etching procedures will be applied in order to study the structural influences on magnetization, in three stages. First, hematite-ilmenite solid solution series with y > 0.5 will be produced as powder samples, using the sealed silica technique and by growing single crystals following the Czochralsky method. Second, structural and chemical properties will be determined by X-ray diffraction, inductively coupled plasma-mass spectroscopy, and high-resolution transmission electron microscopy. To describe static and dynamic magnetization properties, a combination of measurement methods including dc/ac magnetometry and neutron scattering experiments will be applied. A special focus will be electron spin/ferromagnetic resonance spectroscopy, which can detect magnetic bulk properties as well as configurations of Fe3+ in clusters. Third, the decomposing tendency of the manufactured solid solution powders will be fostered by a combination of annealing and etching. The structural and magnetic properties of the treated samples will be compared with the corresponding starting material in order to characterize and, if possible, to quantify the effects of triggered decomposition on the bulk material.The aim of the proposed project is to provide an insight into the magnetic properties of nano-structures in a well-known binary system which is of relevance for earth sciences. The information deduced from this system can yield to a deeper understanding of the magnetization of the earth crust and of weathering and erosion processes on a geological scale. The project will also contribute to the fundamentals of magneto-mineralogy on the nano-scale, opening the way to various functional applications in material science.