Stabilization of weak ferromagnetism by strong magnetic response to epitaxial strain in multiferroic BiFeO3.

Hemant Dixit,Satoshi Okamoto,Jun Hee Lee,Valentino R Cooper,Jaron T Krogel

doi:10.1038/srep12969

Hemant Dixit, Satoshi Okamoto + Show 3 more

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https://doi.org/10.1038/srep12969

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Journal: Scientific reports	Publication Date: Aug 6, 2015
Citations: 18	License type: CC BY 4.0

Affiliation: Oak Ridge National Laboratory

Abstract

Multiferroic BiFeO3 exhibits excellent magnetoelectric coupling critical for magnetic information processing with minimal power consumption. However, the degenerate nature of the easy spin axis in the (111) plane presents roadblocks for real world applications. Here, we explore the stabilization and switchability of the weak ferromagnetic moments under applied epitaxial strain using a combination of first-principles calculations and group-theoretic analyses. We demonstrate that the antiferromagnetic moment vector can be stabilized along unique crystallographic directions ([110] and [–110]) under compressive and tensile strains. A direct coupling between the anisotropic antiferrodistortive rotations and the Dzyaloshinskii-Moria interactions drives the stabilization of the weak ferromagnetism. Furthermore, energetically competing C- and G-type magnetic orderings are observed at high compressive strains, suggesting that it may be possible to switch the weak ferromagnetism “on” and “off” under the application of strain. These findings emphasize the importance of strain and antiferrodistortive rotations as routes to enhancing induced weak ferromagnetism in multiferroic oxides.

Highlights

Widely studied in both the tensile and compressive regimes, the evolution of the wFM under applied epitaxial strain remains relatively unexplored area1,9,10
We neglect the long-range spin-cycloid (62 nm period) phase that occurs in bulk BiFeO311–15 and the possibility of thermal vibrations16,17, our theoretical predictions should be relevant for thin films under epitaxial strain at low temperatures as this spin-cycloid is broken with a small amount of epitaxial strain (− 1.7% ~ 0.5%
We find that the stabilization of wFM is driven by the interplay between the Dzyaloshinskii-Moria (DM) interactions and the single ion anisotropy (SIA); with the DM interactions dominating under tensile strains and the SIA interactions having significant contributions under large compressive strains

Summary

Introduction

Widely studied in both the tensile and compressive regimes, the evolution of the wFM under applied epitaxial strain remains relatively unexplored area. We systemically investigate the influence of epitaxial strain on the underlying mechanisms that link wFM with lattice distortions. For this purpose, we perform non-collinear spin-polarised density functional theory (DFT) calculations including spin-orbit couplings under applied compressive and tensile strains. We observe that at high compressive strains (≥− 7%), the C- and G-type magnetic orderings compete, energetically. Group-theoretic analyses indicate a loss of weak ferromagnetism for C-type magnetic ordering, which is confirmed by DFT calculations. Our study offers useful insights for manipulating the distinct magnetic response of a material under epitaxial strain and has important implications towards utilizing the magnetoelectric effect in BiFeO3 thin films for future technology

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