Multiferroicity and magnetoelectric effect in novel complex oxides.

摘要

Multiferroic materials, in which ferroelectric and magnetic ordering are simultaneously present, exhibit unprecedented physical properties due to the coupling between electric and magnetic order parameters. The significant cross-coupling effects in the newly found materials have invigorated research in multiferroics as they offer a new route toward fundamental understanding of how spin and lattice degrees of freedom interact and produce macroscopic phenomena. Furthermore, the emergence of multiple functional properties in such materials has stimulated the application in future generations of novel devices in which polarization can be controlled by a magnetic field or vice versa. Recently, the search for an enhanced coupling between dual order parameters has led to discoveries of new class of materials called magnetism-driven ferroelectrics. In such materials, ferroelectricity is induced by a fundamental new mechanism, by which magnetic orders with broken inversion symmetry result in ferroelectric distortions through exchange striction. The magnetic origin of their ferroelectricity engenders highly sensible ferroelectric properties to applied magnetic fields. Herein, we present discoveries of new multiferroics which reveal intriguing interplays between ferroelectricity and magnetism: (1) Thermal and magnetic reversal of electric polarization in the conical spiral multiferroic, CoCr 2O4, (2) Collinear-magnetism-induced ferroelectricity of the Ising chain magnet Ca3CoMnO6, and (3) Multiferroicity in the square-lattice antiferromagnet of Ba2CoGe2O 7. The rich physical phenomena among these new materials unveil a fascinating nature of multiferroicity.