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

Dixit H, Lee JH, Krogel JT, Okamoto S, Cooper VR - Sci Rep (2015)

Bottom Line: 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.We demonstrate that the antiferromagnetic moment vector can be stabilized along unique crystallographic directions ([110] and [-110]) under compressive and tensile strains.

View Article: PubMed Central - PubMed

Affiliation: Materials Science and Technology Division, Oak Ridge National Lab, Oak Ridge, TN 37830, USA.

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.

No MeSH data available.


Related in: MedlinePlus

(a) Schematic of the BiFeO3 crystal structure showing the polarisation direction and the plane (red hexagon) perpendicular to the [111] polarisation direction (b) Calculated magnetic energy landscape the bulk rhombohedral phase. The dark band in this plot depicts all possible orientations of the easy spin axis which are found to be degenerate in the (111) plane perpendicular to the [111] direction. Consequently, the spontaneous weak ferromagnetism (Ms) is also degenerate in the (111) plane in such a way that D, L and Ms forms a right handed system.
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f1: (a) Schematic of the BiFeO3 crystal structure showing the polarisation direction and the plane (red hexagon) perpendicular to the [111] polarisation direction (b) Calculated magnetic energy landscape the bulk rhombohedral phase. The dark band in this plot depicts all possible orientations of the easy spin axis which are found to be degenerate in the (111) plane perpendicular to the [111] direction. Consequently, the spontaneous weak ferromagnetism (Ms) is also degenerate in the (111) plane in such a way that D, L and Ms forms a right handed system.

Mentions: Non-collinear DFT calculations within the LDA + U formalism including spin-orbit coupling find that the magnetic ground state of the rhombohedral (R3c) structure exhibits G-type anti-ferromagnetic ordering. Furthermore, these collinear magnetic moments are canted due to the DM interactions and result in an induced wFM. In agreement with previous first principles calculations18, we find that the easy spin axis (i.e. the direction of the induced wFM) is degenerate and lies in a plane perpendicular to the polarisation ([111]) direction. Thus the weak ferromagnetic moments may lie along any one of six possible crystallographic directions ([10–1], [–211], [–110], [–121], [01–1] and [11–2]) which are perpendicular to the polarisation vector19, (see Fig. 1a). Here, we make use of spherical polar coordinates (m, θ and φ) to calculate the magnetic energy landscape along all possible crystallographic directions. For this purpose, m is taken as the magnetic moment on an Fe atom, θ is defined as the angle between the initial collinear arrangement of the magnetic moments and the z-axis (θ ∈ [0; 180]) and φ is the angle between the magnetic moment and the x-axis (φ ∈ [0; 360]) along which the magnetic moments are constrained. Both θ and φ are varied in steps of 15°, resulting in a total of 288 non-collinear calculations at each strain value. These calculations were performed in a high-throughput fashion using the Nexus workflow automation system20. As depicted in Fig. 1b), we observe that the maximum energy configuration (the bright red and white region) corresponds to θ = 54.73 and φ = 45°, which is precisely the direction of the polarisation vector along the [111] direction. The minimum energy configurations (dark black region), on the other hand, show that the antiferromagnetic vector (L) is degenerate in a plane that is perpendicular to the polarisation vector. Thus, as a consequence the easy spin axis corresponding to the induced weak ferromagnetism is also degenerate in the (111) plane. An energy difference of ~2 meV was observed between magnetic moments aligned parallel and perpendicular to the polarisation vector.


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

Dixit H, Lee JH, Krogel JT, Okamoto S, Cooper VR - Sci Rep (2015)

(a) Schematic of the BiFeO3 crystal structure showing the polarisation direction and the plane (red hexagon) perpendicular to the [111] polarisation direction (b) Calculated magnetic energy landscape the bulk rhombohedral phase. The dark band in this plot depicts all possible orientations of the easy spin axis which are found to be degenerate in the (111) plane perpendicular to the [111] direction. Consequently, the spontaneous weak ferromagnetism (Ms) is also degenerate in the (111) plane in such a way that D, L and Ms forms a right handed system.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4526888&req=5

f1: (a) Schematic of the BiFeO3 crystal structure showing the polarisation direction and the plane (red hexagon) perpendicular to the [111] polarisation direction (b) Calculated magnetic energy landscape the bulk rhombohedral phase. The dark band in this plot depicts all possible orientations of the easy spin axis which are found to be degenerate in the (111) plane perpendicular to the [111] direction. Consequently, the spontaneous weak ferromagnetism (Ms) is also degenerate in the (111) plane in such a way that D, L and Ms forms a right handed system.
Mentions: Non-collinear DFT calculations within the LDA + U formalism including spin-orbit coupling find that the magnetic ground state of the rhombohedral (R3c) structure exhibits G-type anti-ferromagnetic ordering. Furthermore, these collinear magnetic moments are canted due to the DM interactions and result in an induced wFM. In agreement with previous first principles calculations18, we find that the easy spin axis (i.e. the direction of the induced wFM) is degenerate and lies in a plane perpendicular to the polarisation ([111]) direction. Thus the weak ferromagnetic moments may lie along any one of six possible crystallographic directions ([10–1], [–211], [–110], [–121], [01–1] and [11–2]) which are perpendicular to the polarisation vector19, (see Fig. 1a). Here, we make use of spherical polar coordinates (m, θ and φ) to calculate the magnetic energy landscape along all possible crystallographic directions. For this purpose, m is taken as the magnetic moment on an Fe atom, θ is defined as the angle between the initial collinear arrangement of the magnetic moments and the z-axis (θ ∈ [0; 180]) and φ is the angle between the magnetic moment and the x-axis (φ ∈ [0; 360]) along which the magnetic moments are constrained. Both θ and φ are varied in steps of 15°, resulting in a total of 288 non-collinear calculations at each strain value. These calculations were performed in a high-throughput fashion using the Nexus workflow automation system20. As depicted in Fig. 1b), we observe that the maximum energy configuration (the bright red and white region) corresponds to θ = 54.73 and φ = 45°, which is precisely the direction of the polarisation vector along the [111] direction. The minimum energy configurations (dark black region), on the other hand, show that the antiferromagnetic vector (L) is degenerate in a plane that is perpendicular to the polarisation vector. Thus, as a consequence the easy spin axis corresponding to the induced weak ferromagnetism is also degenerate in the (111) plane. An energy difference of ~2 meV was observed between magnetic moments aligned parallel and perpendicular to the polarisation vector.

Bottom Line: 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.We demonstrate that the antiferromagnetic moment vector can be stabilized along unique crystallographic directions ([110] and [-110]) under compressive and tensile strains.

View Article: PubMed Central - PubMed

Affiliation: Materials Science and Technology Division, Oak Ridge National Lab, Oak Ridge, TN 37830, USA.

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.

No MeSH data available.


Related in: MedlinePlus