Magnetic and electric phase control in epitaxial EuTiO$_3$ from first principles

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  • 26 June 2006
Abstract
There is great interest in multiferroic materials in which ferroelectric and ferromagnetic ordering not only coexist, but in which the electrical polarization and the magnetization are also strongly coupled~\cite{fiebig.review,spaldin.fiebig}. With recent successes in the application of first-principles density-functional methods to the design of new multiferroics~\cite{ederer.review}, the focus has now turned to how to produce a strong coupling between the two distinct order parameters~\cite{tokura.2006}. In this paper, we present a first-principles calculation of the ground-state epitaxial phase diagram for the magnetic perovskite EuTiO$_3$. Epitaxial strain can have profound effects on the properties of thin films, even driving systems through phase transitions. We show that in EuTiO$_3$, epitaxial strain can be used to dial into the region of the phase diagram where, due to spin-phonon coupling, magnetic (electric) phase control can be achieved by an applied electric (magnetic) field. This phase-control region is bordered by a divergent magnetocapacitance on the low strain side and a phase transition from the non-polar antiferromagnetic phase to a previously unknown ferroelectric-ferromagnetic phase on the high strain side. This work is a realization of a new approach for achieving ferroelectricity with substantial polarization whose origin lies in the ordering of spins.

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