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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

Calculated single ion anisotropy vector (Kn) as a function of applied epitaxial strain.(a) The magnitude and (b) The direction of the easy spin axis with respect to the z-axis. The inset shows the relative sinusoidal variations of the single ion anisotropy. The energy minimum (indicated with red arrow) for the bulk ground state corresponds to 54° i.e. along the [111] direction. The applied epitaxial strain shifts the energy minimum (indicated using black and cyan arrows) toward the z-axis and the x-y plane for compressive and tensile strains, respectively.
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f5: Calculated single ion anisotropy vector (Kn) as a function of applied epitaxial strain.(a) The magnitude and (b) The direction of the easy spin axis with respect to the z-axis. The inset shows the relative sinusoidal variations of the single ion anisotropy. The energy minimum (indicated with red arrow) for the bulk ground state corresponds to 54° i.e. along the [111] direction. The applied epitaxial strain shifts the energy minimum (indicated using black and cyan arrows) toward the z-axis and the x-y plane for compressive and tensile strains, respectively.

Mentions: To analyse the spin polarisation along the unique [110] and [–110] directions, we calculated the DM interactions and SIA for each strained phase. It is important to recall that the spin canting is induced by the AFD rotations and hence, the wFM and by extension the DM interactions may be directly linked to the amplitude of these distortions. The variations in the components of the local DM vector (D{1,2,3}) as a function of applied epitaxial stain are shown in Fig. 4. For the rhombohedral structure, we have isotropic DM interactions with /D1/ = /D2/ = /D3/ = 304 μeV. On the other hand, the calculated SIA (refer to Fig. 5) is merely 11 μeV (which compares well with the experimentally measured value of 3.5 μeV26); significantly lower than the DM interactions and thus does not compete with the DM interactions. It is interesting to note that the easy spin axis (n) actually points exactly along the [111] direction. However, since the energy gain from the isotropic DM interactions is dominant, net spins are polarised along a direction perpendicular to [111]. Furthermore, the rotational symmetry promotes the degeneracy of the easy spin axis in the (111) plane. Hence, as a result of the isotropic DM interactions pointing along the [111] direction both L, the induced weak ferromagnetic moments are degenerate in a plane perpendicular to the polarisation direction.


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)

Calculated single ion anisotropy vector (Kn) as a function of applied epitaxial strain.(a) The magnitude and (b) The direction of the easy spin axis with respect to the z-axis. The inset shows the relative sinusoidal variations of the single ion anisotropy. The energy minimum (indicated with red arrow) for the bulk ground state corresponds to 54° i.e. along the [111] direction. The applied epitaxial strain shifts the energy minimum (indicated using black and cyan arrows) toward the z-axis and the x-y plane for compressive and tensile strains, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f5: Calculated single ion anisotropy vector (Kn) as a function of applied epitaxial strain.(a) The magnitude and (b) The direction of the easy spin axis with respect to the z-axis. The inset shows the relative sinusoidal variations of the single ion anisotropy. The energy minimum (indicated with red arrow) for the bulk ground state corresponds to 54° i.e. along the [111] direction. The applied epitaxial strain shifts the energy minimum (indicated using black and cyan arrows) toward the z-axis and the x-y plane for compressive and tensile strains, respectively.
Mentions: To analyse the spin polarisation along the unique [110] and [–110] directions, we calculated the DM interactions and SIA for each strained phase. It is important to recall that the spin canting is induced by the AFD rotations and hence, the wFM and by extension the DM interactions may be directly linked to the amplitude of these distortions. The variations in the components of the local DM vector (D{1,2,3}) as a function of applied epitaxial stain are shown in Fig. 4. For the rhombohedral structure, we have isotropic DM interactions with /D1/ = /D2/ = /D3/ = 304 μeV. On the other hand, the calculated SIA (refer to Fig. 5) is merely 11 μeV (which compares well with the experimentally measured value of 3.5 μeV26); significantly lower than the DM interactions and thus does not compete with the DM interactions. It is interesting to note that the easy spin axis (n) actually points exactly along the [111] direction. However, since the energy gain from the isotropic DM interactions is dominant, net spins are polarised along a direction perpendicular to [111]. Furthermore, the rotational symmetry promotes the degeneracy of the easy spin axis in the (111) plane. Hence, as a result of the isotropic DM interactions pointing along the [111] direction both L, the induced weak ferromagnetic moments are degenerate in a plane perpendicular to the polarisation direction.

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