Multiferroic and Magnetoelectric Materials

Freitag, 29. Februar, 8:30 Uhr, H 0105

Recently magnetoelectric (ME) materials with a bilinear magnetic and electric free energy contribution, F_me= - αH · E, have become of utmost interest in view of both fundamental understanding and novel desirable applications (Fiebig, 2005). Multiferroic materials with simultaneous polar and magnetic long-range order are expected to optimize the crosslinked responses, viz. magnetization excited by electric fields and electric polarization induced by magnetic ones (Eerenstein et al., 2005). We discuss the occurrence of single phase multiferroicity and of bilinear magnetoelectricity in various systems. Surprisingly most promising applications in spintronics are at present proposed for non-ME multiferroics like BiMnO₃ (Gajek et al., 2007), and for nonmultiferroic magnetoelectrics like Cr₂O₃ (Chen et al., 2006). Best performing ME multiferroics are stress-strain coupled heterophase systems like BaTiO₃/CoFe₂O₄ (Ren et al., 2005). Since recently two extensions of the conventional multiferroic scenario have been under debate. Ferromagnetic-ferroelastic multiferroics as realized by Ni₂MnGa-like magnetic shape memory alloys (Ullacko et al., 1996) complement the framework of ferroics involved. Even multiglass systems are envisaged. Mn-doped quantum paraelectric (Sr,Mn)TiO₃ shows both long-range dipolar and spin-glass ordering and is subject to higher order ME coupling (Bedanta et al., 2007).

Wolfgang Kleemann
Angewandte Physik, Universität Duisburg-Essen, 47048 Duisburg