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TT: Fachverband Tiefe Temperaturen

TT 40: Poster Session Correlated Electrons

TT 40.61: Poster

Mittwoch, 13. März 2013, 15:00–19:00, Poster D

Linear magnetoelectric effects in the cubic ferrimagnetic helimagnet Cu₂OSeO₃: phenomenological theory — Maria Eleni Belesi^1,2, •Ioannis Rousochatzakis², Mohamed Abid^1,3, Ulrich Rössler², Helmut Berger¹, and Jean-Philippe Ansermet¹ — ¹Institut de Physique de la Matiére Condensée, Ecole Polytechnique Fédérale de Lausanne, Station 3, CH-1015 Lausanne-EPFL, Switzerland — ²Leibniz Institute for Solid State and Materials Research, Helmholtzstrasse 20, 01069 Dresden, Germany — ³King Saud University, Riyadh 11451, Saudi Arabia

We present a phenomenological Landau-Ginzburg theory for the linear magnetoelectric (ME) effect in the spin 1/2 compound Cu₂OSeO₃. Single-crystal ME data show two additional phases below the 3up-1down ferrimagnetic state. We demonstrate that these are related to the field-driven evolution of a long-period helical phase, which is stabilized by the chiral Dzyaloshinskii-Moriya term DM· (∇×M) that is present in this noncentrosymmetric compound. The theory is in excellent agreement with experiment, and shows three main features: (i) the polarization P has a uniform as well as a long-wavelength component that follows the magnetic twisting; (ii) the uniform component points along (H_y H_z, H_z H_x, H_x H_y); and (iii) its strength is proportional to η_∥²−η_⊥²/2, where η_∥ and η_⊥ are the longitudinal and transverse components of the magnetic order. Hence, the field dependence of P provides a clear signature of the evolution of a conical helix under a magnetic field. A similar theory is discussed for the magnetocapacitance.