First Principles Studies of Multiferroic Materials

Multiferroics, materials where spontaneous long-range magnetic and dipolar orders coexist, represent an attractive class of compounds, which combine rich and fascinating fundamental physics with a technologically appealing potential for applications in the general area of spintronics. Ab-initio calculations have significantly contributed to recent progress in this area, by elucidating different mechanisms for multiferroicity and providing essential information on various compounds where these effects are manifestly at play. In particular, here we present examples of density-functional theory investigations for two main classes of materials: a) proper multiferroics (where ferroelectricity is driven by hybridization or purely structural effects), with BiFeO_3 as prototype material, and b) improper multiferroics (where ferroelectricity is driven by correlation effects and is strongly linked to electronic degrees of freedom such as spin, charge, or orbital ordering), with rare-earth manganites as prototypes.