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MA: Fachverband Magnetismus

MA 19: Poster I (Bio- and Molecular Magnetism/ Magnetic Particles and Clusters/ Micro- and Nanostructured Magnetic Materials/ Magnetic Materials/ Multiferroics/ Magnetic Shape Memory Alloys/ Electron Theory of Magntism/ Spincaloric Transport/ Magnetic Coupling and Exchange Bias/ Magnetization Dynamics/ Micromagnetism and Computational Magnetics)

MA 19.58: Poster

Dienstag, 15. März 2011, 10:45–13:00, P2

Synthesis optimization of Possible Relaxor Ferroelectric Magnetite crystals — •Shilpa Adiga, Jörg Persson, and Manuel Angst — IFF, JARA-FIT, Forschungszentrum Jülich GmbH, Jülich, Germany

The 120 K Verwey-transition [1] in magnetite Fe₃O₄ is the classical example for charge ordering. Despite of the decades of research, the complex low-temperature structure and even the existence of Fe^2+/3+ charge order is still unresolved. Early experimental studies and recent theoretical calculations on magnetite support ferroelectricity (FE) due to charge ordering. If confirmed, FE, and thus multiferroicity from charge order in classical magnetite would be significant. Recently, Schrettle et al [2] observed signatures of relaxor FE in dielectric spectroscopy measurements. Specific diffuse scattering would be expected in such a case. Unambiguous proof of (relaxor) FE may be obtained by detailed scattering experiments. The sensitivity of the Verwey transition depends on sample quality (oxygen stoichiometry) [3]. The best way to obtain high-quality crystals is the direct synthesis in an appropriate CO/CO₂ flow [4]. We first investigated appropriate ratios of CO/CO₂ at high temperature on polycrystalline samples, characterized primarily by thermo-remanent magnetization and specific heat. The use of the results for the crystal growth by floating zone method and the physical properties of the grown crystals will be presented.

[1] E.J.W.Verwey, Nature 144 327 (1939). [2] F. Schrettle et al., arXive:1007.3613. [3] P. Shepherd et al., Phys. Rev. B. 43 8461 (1991). [4] R.Aragon et al., J. crystal growth,. 61 221 (1983).