Browsing by Author "Krohns, S"

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    FeCr2S4 in magnetic fields: possible evidence for a multiferroic ground state
    (Nature.com, 2014-08-15) Bertinshaw, J; Ulrich, C; Günther, A; Schrettle, F; Wohlauer, M; Krohns, S; Reehuis, M; Studer, AJ; Avdeev, M; Quach, DV; Groza, JR; Tsurkan, V; Loidl, A; Deisenhofer. J.
    We report on neutron diffraction, thermal expansion, magnetostriction, dielectric, and specific heat measurements on polycrystalline FeCr2S4 in external magnetic fields. The ferrimagnetic ordering temperatures TC ≈ 170 K and the transition at TOO ≈ 10 K, which has been associated with orbital ordering, are only weakly shifted in magnetic fields up to 9 T. The cubic lattice parameter is found to decrease when entering the state below TOO. The magnetic moments of the Cr- and Fe-ions are reduced from the spin-only values throughout the magnetically ordered regime, but approach the spin-only values for fields >5.5 T. Thermal expansion in magnetic fields and magnetostriction experiments indicate a contraction of the sample below about 60 K. Below TOO this contraction is followed by a moderate expansion of the sample for fields larger than ~4.5 T. The transition at TOO is accompanied by an anomaly in the dielectric constant. The dielectric constant depends on both the strength and orientation of the external magnetic field with respect to the applied electric field for T < TOO. A linear correlation of the magnetic-field-induced change of the dielectric constant and the magnetic-field dependent magnetization is observed. This behaviour is consistent with the existence of a ferroelectric polarization and a multiferroic ground state below 10 K. © The Authors
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    Neutron diffraction, magnetostriction, and dielectric properties of orbitally ordered FeCr2S4 in external magnetic fields
    (arXiv, 2013-09-09) Bertinshaw, J; Ulrich, C; Günther, A; Schrettle, F; Wohlauer, M; Krohns, S; Reehuis, M; Studer, AJ; Avdeev, M; Quach, DV; Groza, JR; Tsurkan, V; Loidl, A; Deisenhofer, J
    We report on neutron diffraction, thermal expansion, dielectric and specific heat measurements on polycrystalline FeCr2S4 samples in external magnetic fields. The ferrimagnetic and orbital ordering temperatures, T_C = 170K and T_OO = 10 K are only weakly shifted in magnetic fields up to 9 T. The cubic lattice parameter is found to decrease when entering the orbitally ordered state below T_OO. This contraction does not significantly change in external fields up to 7.5 T. The magnetic moments of the Cr and Fe ions are reduced from the spin-only values throughout the magnetically ordered regime. The moments start to increase in the orbitally ordered regime when the magnetic fields become larger than 4.5 T and approach the expected spin-only values above about 5.5 T. Thermal expansion in magnetic fields and magnetostriction experiments indicate a contraction of the sample due to magnetic domains below about 60 K. In the orbitally ordered state this contraction is followed by a moderate expansion of the sample for fields larger than about 4.5 T, coinciding with the onset of the increase of the magnetic moments. The orbital ordering transition is accompanied by an anomaly in the dielectric constant. Below T_OO the dielectric constant depends on both the strength of the external magnetic field as well as the orientation of the external magnetic field with respect to the applied electric field.