Berlin 2012 – wissenschaftliches Programm
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DS: Fachverband Dünne Schichten
DS 10: Multiferroics II: Hexagonal manganites / Incommensurate multiferroics (jointly with MA, DF, KR, TT)
DS 10.11: Vortrag
Montag, 26. März 2012, 18:00–18:15, EB 301
Theory of High-Temperature Multiferroicity in CuO — •Naëmi Leo1,2, Pierre Tolédano3, Dmitry D. Khalyavin4, and Manfred Fiebig1,2 — 1ETH Zurich, Switzerland — 2HISKP, Universität Bonn, Germany — 3University of Picardie, France — 4ISIS, United Kingdom
Spin-spiral multiferroics offer strong magnetoelectric coupling, although most of them have low transition temperatures which make them undesirable for technical applications. Cupric oxide is a remarkable exception with its high Curie temperature of 230 K. Understanding the interactions leading to such a high-TC magnetically induced ferroelectricity is very desirable for future room-temperature magnetoelectric multiferroics devices.
Here we present a Landau theory analysis of the multiferroic properties of CuO [1]. Using a multi-dimensional order parameter expansion of the free energy we examine the sequence of phase transitions: The unusual direct transition to the multiferroic phase is induced by the simultaneous onset of two order parameters, enabled by the strong Cu-O superexchange. Expressing the order parameter in terms of spins we determine theoretically the magnetic structure in the spin-spiral phases. Furthermore we identify the microscopic interactions responsible for the magnetically induced spontaneous polarization.
The work in Bonn was supported by the DFG through the SFB 608.
[1] P. Toledano, N. Leo, D.D. Khalyavin, L.C. Chapon, T. Hoffmann, D. Meier, and M. Fiebig, Phys. Rev. Lett. 106, 257601 (2011).