Berlin 2012 – scientific programme

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DF: Fachverband Dielektrische Festkörper

DF 8: Multiferroics III (jointly with MA, DS, KR, TT)

DF 8.9: Talk

Tuesday, March 27, 2012, 11:45–12:00, EB 301

Relaxor ferroelectricity in pure and doped magnetite — •Eugen Ruff¹, Florian Schrettle¹, Stephan Krohns¹, Peter Lunkenheimer¹, Victor A. M. Brabers², and Alois Loidl¹ — ¹Experimental Physics V, University of Augsburg, 86135 Augsburg, Germany — ²Department of Physics, Eindhoven University of Technology, 5600 MB Eindhoven, Netherlands

A possible example for a multiferroic material is the extensively studied magnetite Fe₃O₄, which shows charge-order (CO) below the Verwey transition at T_V ≈ 120 K and is ferrimagnetically ordered below 500 K¹. As shown in the present contribution, dielectric spectroscopy reveals a relaxation below T_V, indicating relaxorlike polar order in Fe₃O₄². We find long-range ferroelectric order to be impeded by the continuous freezing of polar degrees of freedom and the formation of a tunneling-dominated glasslike state of electrons at low temperatures. To reveal the origin of the ferroelectric state, whose dielectric signature is partly superimposed by a so called Maxwell-Wagner (MW) relaxation, we have investigated doped samples with Al, Ga, and Mg. The dielectric spectra of these doped samples (< 2%) provide further evidence for the relaxor ferroelectric state of Fe₃O₄ and demonstrate the influence of the MW relaxation.

¹D. I. Khomskii, J. Magn. Magn. Mater. 306, 1 (2006).

²F. Schrettle et al., Phys. Rev. B 83, 195109 (2011).