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Intrinsic decomposing tendency of hematite-ilmenite phases and its effect on static and dynamic magnetic properties

English title Intrinsic decomposing tendency of hematite-ilmenite phases and its effect on static and dynamic magnetic properties
Applicant Gehring Andreas
Number 134806
Funding scheme Project funding
Research institution Institut für Geophysik ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Mineralogy
Start/End 01.04.2011 - 31.03.2013
Approved amount 118'054.00
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All Disciplines (2)

Discipline
Mineralogy
Material Sciences

Keywords (16)

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

Lay Summary (English)

Lead
Lay summary
The hematite-ilmenite solid solution series ((1-x) Fe2O3 -x FeTiO3; 0 < x <1) is characterized by an intrinsic decomposing tendency that has been investigated in rock bodies and by thermodynamic modeling. The atomic arrangement of the two valence-states, Fe(II) and Fe(III), in hemo-ilmenite generates a stochastic magnetic structure. This project pursues the detailed study of the thermodynamic magnetic properties of the system, experimentally and by means of numerical simulations. The hemo-ilmenite system is a solid solution of hematite Fe2O3 and ilmenite FeTiO3; both end-members are semiconductors and antiferromagnets with ordering temperature 950 K and 58 K, respectively. The solid solution orders as a ferrimagnet for x > 0.5 and as antiferromagnet for x < 0.5 with an ordering temperature which is linear to the composition x. The presence of the two valence states of iron, Fe(II) with spin 4/2 and Fe(III) with spin 5/2, generates a complex magnetic structure, which exhibits characteristic coupling phenomena. An example is the spin-glass freezing at low temperature (T < 50 K). Although the system has been studied extensively for the past 30 years, the interaction mechanisms in the magnetic structure remain unclear. The objective of the project is to attain a deeper understanding of the coupling-mechanisms in hemo-ilmenite. In order to achieve this goal synthetic solid solutions are fabricated and their structures are investigated by X-ray diffraction. The magnetic properties of the synthetic and natural solid solutions are examined in a magnetometer at low-temperature using both static and dynamic methods and the results are evaluated using mean-field-theory considerations. Due to the complex interaction-patterns in the system, analytic methods can only be used up to a certain point. Therefore, the study is completed by mans of Monte Carlo simulations, which is a powerful tool to describe such stochastic problems. The hemo-ilmenite system constitutes the only frustrated magnetic system with a naturally occurring equivalent. Studying the system offers the possibility to better understand such stochastic spin-structures, as they occur in nature. The magnetic information provides a detailed insight into the molecular structure of the solid solution, and, therefore, opens the door to decipher the geological origin of natural samples. In addition, the unique combination of semiconduction and ferrimagnetism can be exploited to design new materials for technological applications in spintronics. Therefore, the system is of multidisciplinary interest in the solid state physics, geophysics, and materials science community.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Publications

Publication
Steep energy landscapes and adjustable magnetization status in a four-layer mean-field model with competing interactions
Charilaou M, Sahu K.K, Gehring A.U., Löffler J.F. (2012), Steep energy landscapes and adjustable magnetization status in a four-layer mean-field model with competing interactions, in PHYSICAL REVIEW B, 86(10), 104415-1-104415-6.
Large spontaneous magnetostriction in FeTiO3 and adjustable magnetization states in Fe(III)-doped FeTiO3
Charilaou M., Sheptyakov D., Löffler J.F., Gehring A.U. (2012), Large spontaneous magnetostriction in FeTiO3 and adjustable magnetization states in Fe(III)-doped FeTiO3, in PHYSICAL REVIEW B, 86(02), 024439-1-024439-11.
Magnetic thermodynamics as proxy for chemical inhomogeneity in hemo-ilmenite solid solutions
Charilaou M, Loffler JF, Gehring AU (2012), Magnetic thermodynamics as proxy for chemical inhomogeneity in hemo-ilmenite solid solutions, in PHYSICS AND CHEMISTRY OF MINERALS, 39(2), 87-92.
Monte Carlo study of partitioning mechanisms in mixed-spin Ising systems
Charilaou M, Sahu KK, Gehring AU, Loffler JF (2011), Monte Carlo study of partitioning mechanisms in mixed-spin Ising systems, in PHYSICAL REVIEW B, 84(22), 224434-1-224434-5.
Evolution of magnetic anisotropy and thermal stability during nanocrystal-chain growth
Charilaou M, Sahu KK, Faivre D, Fischer A, Garcia-Rubio I, Gehring AU (2011), Evolution of magnetic anisotropy and thermal stability during nanocrystal-chain growth, in APPLIED PHYSICS LETTERS, 99(18), 182504-1-182504-3.
Interaction-Induced Partitioning and Magnetization Jumps in the Mixed-Spin Oxide FeTiO3-Fe2O3
Charilaou M, Sahu KK, Zhao S, Loffler JF, Gehring AU (2011), Interaction-Induced Partitioning and Magnetization Jumps in the Mixed-Spin Oxide FeTiO3-Fe2O3, in PHYSICAL REVIEW LETTERS, 107(5), 057202-1-057202-4.
Slow dynamics and field-induced transitions in a mixed-valence oxide solid solution
Charilaou M, Loffler JF, Gehring AU (2011), Slow dynamics and field-induced transitions in a mixed-valence oxide solid solution, in PHYSICAL REVIEW B, 83(22), 224414-1-224414-7.
Fe-Ti-O exchange at high temperature and thermal hysteresis
Charilaou M, Loffler JF, Gehring AU (2011), Fe-Ti-O exchange at high temperature and thermal hysteresis, in GEOPHYSICAL JOURNAL INTERNATIONAL, 185(2), 647-652.
Simulation of ferromagnetic resonance spectra of linear chains of magnetite nanocrystals
Charilaou M, Winklhofer M, Gehring AU (2011), Simulation of ferromagnetic resonance spectra of linear chains of magnetite nanocrystals, in JOURNAL OF APPLIED PHYSICS, 109(9), 093903-1-093903-6.

Collaboration

Group / person Country
Types of collaboration
PSI Switzerland (Europe)
- Publication

Communication with the public

Communication Title Media Place Year
Print (books, brochures, leaflets) Magnetic interactions -From nature to laboratory International 01.10.2012

Associated projects

Number Title Start Funding scheme
121844 Intrinsic decomposing tendency of hematite-ilmenite phases and its effect on static and dynamic magnetic properties 01.02.2009 Project funding
153173 Magnetic thermodynamics of non-stoichiometric Fe-based mineral phases 01.04.2014 Project funding

Abstract

The hematite-ilmenite solid solution series (x)FeTiO3-(1-x)Fe2O3 is a binary system relevant in physics and earth sciences because of its magnetic properties. The solid solution series contains magnetic phases with ferrimagnetic and antiferromagnetic ordering and phases in a spin-glass-like disordered state. The magnetic behavior of this solid solution represents a classic example of oxide magnetism for basic research. The combination of intrinsic ferrimagnetism and semiconductivity can be beneficial for spintronics applications, and the direct relation between composition factor x and magnetic properties can be used as proxy in order to deduce the thermal evolution of intrusive and volcanic rock bodies. The project, which started in February 2009, aims for a profound understanding of the magnetic properties of the solid solution series, with special attention on the decay of the long-range ordering and the generation of a spin-glass-like state. In the first year of the project the emphasis was on the fabrication of the solid solutions with x > 0.5 and their magnetic characterization with ac/dc magnetometry. The preparation procedure was successful for powder samples and a paper on Ti and Fe cation diffusion in the solid solutions has been submitted for publication. In contrast to the powder samples, the manufacturing of single crystals is not yet solved. Magnetometry of single-phase hemo-ilmenite powder samples with x = 0.7, 0.8, and 0.9 showed that spin-glass freezing takes place at T < 30 K. An atomistic model was developed in order to explain the freezing; its prediction for the freezing temperature agrees reasonably well with the experimental data. These findings are being prepared for publication. Furthermore, the higher harmonics of the ac susceptibility were recorded at the onset of magnetic ordering for hemo-ilmenite solid solution with x = 0.9. To our knowledge, for the first time, such measurement has been performed on an oxide material. The higher harmonics probe intrinsic magnetic processes, which are not easily detectable by other methods. These studies will be put forward in depth in order to analyze the internal magnetic structure of the solid solution. The project will be continued as planned with neutron scattering and ferromagnetic resonance spectroscopy (FMR) experiments. With neutron scattering, the structural and magnetic clustering of the disordered solid solution can be probed. This information will be used to better model the magnetic behavior of the system. The FMR experiments probe the dynamics of the magnetic order and can reveal the intrinsic damping mechanisms. This is of great interest since the non-metallic character of the electron structure gives rise to more complicated damping mechanisms for the magnetic precession. The experimental and numerical approach will provide detailed insight into this classical solid-solution system and it will reveal the dynamics of changes in the long-range magnetic properties. Such information is fundamental for earth scientists studying magnetization of large rock bodies but also for physicists and material scientists dealing with the stability of magnetic devices. Because of the broad variety of the magnetic pattern found in hemo-ilmenite solid solutions, they can be considered as model system for the investigation of the correlation between magnetic and electronic properties, which is of fundamental physical and mineralogical interest. A fourth year is planned in which experiments will be performed involving UV spectroscopy in order to reveal the correlation between band gap and magnetic order. Such information can open the door for advanced magneto-mineralogy and for technological applications in spintronics.
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