Dresden 2006 – scientific programme

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SYMM: Multi-ferroic materials

SYMM 2: Multiferroic Materials - Experiment

SYMM 2.4: Invited Talk

Tuesday, March 28, 2006, 17:45–18:15, HSZ 04

Magnetoelectric Effects in Multiferroics — •A. Loidl, J. Hemberger, A. Pimenov, P. Lunkenheimer, A. A. Mukhin, and V. Tsurkan — Center for Electronic Correlations and Magnetism, University of Augsburg, Germany

Magnetoelectric phenomena were investigated for two different multiferroic systems. The coupling of dielectric and magnetic properties and the simultaneous occurrence of long-range magnetic and polar order are discussed for manganites and spinels. A phase diagram of Eu_1−xGd_xMnO₃ as function of temperature and magnetic field is established. It resembles the main features of the well-known magneto-electric phase diagram of RMnO₃ (R = rare earth) with a sequence of magnetic and polar phase transitions for varying ionic radii of the rare earth ions. Special attention is paid to the occurrence of electromagnons, i.e. spin waves that can only be excited by an ac electric field. These excitations also allow tuning the index of refraction by moderate magnetic fields. In the second part we discuss the simultaneous appearance of colossal magneto-resistance and colossal magneto-capacitance effects in chromium sulfo spinels. Ferroelectricity appears well above the onset of ferromagnetism in CdCr₂S₄ and above a complex antiferromagnetic order in HgCr₂S₄. We speculate that the occurrence of ferroelectricity in these multiferroic compounds is rather of electronic than of ionic origin.