A three-order-parameter bistable magnetoelectric multiferroic metal

Abstract

Using first-principles calculations we predict that the layered-perovskite metal Bi${}_5$Mn${}_5$O${}_{17}$ is a ferromagnet, ferroelectric, and ferrotoroid which may realize the long sought-after goal of a room-temperature ferromagnetic single-phase multiferroic with large, strongly coupled, primary-order polarization and magnetization. Bi${}_5$Mn${}_5$O${}_{17}$ has two nearly energy-degenerate ground states with mutually orthogonal vector order parameters (polarization, magnetization, ferrotoroidicity), which can be rotated globally by switching between ground states. Giant cross-coupling magnetoelectric and magnetotoroidic effects, as well as optical non-reciprocity, are thus expected. Importantly, Bi${}_5$Mn${}_5$O${}_{17}$ should be thermodynamically stable in O-rich growth conditions, and hence experimentally accessible.

7 pages, 7 figures

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