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Lattice-distortion Induced Magnetic Transition from Low-temperature Antiferromagnetism to High-temperature Ferrimagnetism in Double Perovskites A2FeOsO6 (A = Ca, Sr).

Hou YS, Xiang HJ, Gong XG - Sci Rep (2015)

Bottom Line: High-temperature insulating ferrimagnetism is investigated in order to further reveal its physical mechanisms, as well as identify potentially important scientific and practical applications relative to spintronics.Also discussed is the 5d(3)-3d(5) superexchange.We propose that such superexchange is intrinsically antiferromagnetic instead of ferromagnetic as previously thought.

View Article: PubMed Central - PubMed

Affiliation: Key Laboratory of Computational Physical Sciences (Ministry of Education), State Key Laboratory of Surface Physics, and Department of Physics, Fudan University, Shanghai 200433, People's Republic of China.

ABSTRACT
High-temperature insulating ferrimagnetism is investigated in order to further reveal its physical mechanisms, as well as identify potentially important scientific and practical applications relative to spintronics. For example, double perovskites such as Sr2FeOsO6 and Ca2FeOsO6 are shown to have puzzling magnetic properties. The former is a low-temperature antiferromagnet while the latter is a high-temperature insulating ferrimagnet. In order to understand the underlying mechanisms, we have investigated the frustrated magnetism of A2FeOsO6 by employing density functional theory and maximally-localized Wannier functions. We find lattice distortion enhances the antiferromagnetic nearest-neighboring Fe-O-Os interaction, however weakens the antiferromagnetic interactions via the Os-O-O-Os and Fe-O-Os-O-Fe paths, so is therefore responsible for the magnetic transition from the low-temperature antiferromagnetism to the high-temperature ferrimagnetism as the decrease of the A(2+) ion radii. Also discussed is the 5d(3)-3d(5) superexchange. We propose that such superexchange is intrinsically antiferromagnetic instead of ferromagnetic as previously thought. Our work clearly illustrates the magnetic frustration can be effectively relieved by lattice distortion, thus paving the way for tuning of complex magnetism in yet other 3d-5d (4d) double perovskites.

No MeSH data available.


Related in: MedlinePlus

Mechanism by which lattice distortion enhances the NN AFM interaction between Fe3+ and Os5+ ions(a), and weakens the NNN AFM interaction between Os5+ ions (b) in Ca2FeOsO6. Solid (dashed) lines with double arrowheads indicate the electron hopping causing AFM (FM) contribution to the NN superexchange or NNN super-superexchange. S and W represent “strong” and “weak” words, respectively. In (a), the FM contribution of ax = 0 is weaker than that of ax = 1. However, the AFM contribution of ax = 0 is stronger than that of ax = 1. In (b), the AFM contribution of ax = 0 is weaker than that of ax = 1. Insets in (a,b) are for the local structures of Fe-O-Os and Os-O-O-Os paths, respectively. The relevant bond angles, bond lengths and calculated magnetic exchange constants are explicitly given in the inset of figures (a) and (b).
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f3: Mechanism by which lattice distortion enhances the NN AFM interaction between Fe3+ and Os5+ ions(a), and weakens the NNN AFM interaction between Os5+ ions (b) in Ca2FeOsO6. Solid (dashed) lines with double arrowheads indicate the electron hopping causing AFM (FM) contribution to the NN superexchange or NNN super-superexchange. S and W represent “strong” and “weak” words, respectively. In (a), the FM contribution of ax = 0 is weaker than that of ax = 1. However, the AFM contribution of ax = 0 is stronger than that of ax = 1. In (b), the AFM contribution of ax = 0 is weaker than that of ax = 1. Insets in (a,b) are for the local structures of Fe-O-Os and Os-O-O-Os paths, respectively. The relevant bond angles, bond lengths and calculated magnetic exchange constants are explicitly given in the inset of figures (a) and (b).

Mentions: Figure 3a demonstrates the mechanism by which lattice distortion enhances the NN Fe-O-Os AFM interaction. For illustration purposes, we consider the Fe-O-Os path along the c axis as an example. Fig. S1 of the SM shows the detailed leading hopping integrals and energy levels in the relaxed and pseudo-cubic structures, respectively. These hopping integrals clearly indicate lattice distortion tremendously reduces the electron hopping between the occupied eg orbitals of Fe3+ ions and the unoccupied one of Os5+ ions. Consequently, one can conclude based on the formula of Jij (see Eq. (2)) that lattice distortion extraordinarily reduces the FM contribution to the NN superexchange. In contrast, lattice distortion has a rather minor effect on the AFM contribution, because it increases the electrons hopping between the occupied eg orbitals of Fe3+ ions and the occupied t2g orbitals of Os5+ ions, although it reduces the hopping between the occupied t2g orbitals of Fe3+ and Os5+ ions. Therefore, lattice distortion enhances the NN AFM interaction by dramatically reducing the FM contribution, and by maintaining the AFM contribution almost unchanged.


Lattice-distortion Induced Magnetic Transition from Low-temperature Antiferromagnetism to High-temperature Ferrimagnetism in Double Perovskites A2FeOsO6 (A = Ca, Sr).

Hou YS, Xiang HJ, Gong XG - Sci Rep (2015)

Mechanism by which lattice distortion enhances the NN AFM interaction between Fe3+ and Os5+ ions(a), and weakens the NNN AFM interaction between Os5+ ions (b) in Ca2FeOsO6. Solid (dashed) lines with double arrowheads indicate the electron hopping causing AFM (FM) contribution to the NN superexchange or NNN super-superexchange. S and W represent “strong” and “weak” words, respectively. In (a), the FM contribution of ax = 0 is weaker than that of ax = 1. However, the AFM contribution of ax = 0 is stronger than that of ax = 1. In (b), the AFM contribution of ax = 0 is weaker than that of ax = 1. Insets in (a,b) are for the local structures of Fe-O-Os and Os-O-O-Os paths, respectively. The relevant bond angles, bond lengths and calculated magnetic exchange constants are explicitly given in the inset of figures (a) and (b).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4542468&req=5

f3: Mechanism by which lattice distortion enhances the NN AFM interaction between Fe3+ and Os5+ ions(a), and weakens the NNN AFM interaction between Os5+ ions (b) in Ca2FeOsO6. Solid (dashed) lines with double arrowheads indicate the electron hopping causing AFM (FM) contribution to the NN superexchange or NNN super-superexchange. S and W represent “strong” and “weak” words, respectively. In (a), the FM contribution of ax = 0 is weaker than that of ax = 1. However, the AFM contribution of ax = 0 is stronger than that of ax = 1. In (b), the AFM contribution of ax = 0 is weaker than that of ax = 1. Insets in (a,b) are for the local structures of Fe-O-Os and Os-O-O-Os paths, respectively. The relevant bond angles, bond lengths and calculated magnetic exchange constants are explicitly given in the inset of figures (a) and (b).
Mentions: Figure 3a demonstrates the mechanism by which lattice distortion enhances the NN Fe-O-Os AFM interaction. For illustration purposes, we consider the Fe-O-Os path along the c axis as an example. Fig. S1 of the SM shows the detailed leading hopping integrals and energy levels in the relaxed and pseudo-cubic structures, respectively. These hopping integrals clearly indicate lattice distortion tremendously reduces the electron hopping between the occupied eg orbitals of Fe3+ ions and the unoccupied one of Os5+ ions. Consequently, one can conclude based on the formula of Jij (see Eq. (2)) that lattice distortion extraordinarily reduces the FM contribution to the NN superexchange. In contrast, lattice distortion has a rather minor effect on the AFM contribution, because it increases the electrons hopping between the occupied eg orbitals of Fe3+ ions and the occupied t2g orbitals of Os5+ ions, although it reduces the hopping between the occupied t2g orbitals of Fe3+ and Os5+ ions. Therefore, lattice distortion enhances the NN AFM interaction by dramatically reducing the FM contribution, and by maintaining the AFM contribution almost unchanged.

Bottom Line: High-temperature insulating ferrimagnetism is investigated in order to further reveal its physical mechanisms, as well as identify potentially important scientific and practical applications relative to spintronics.Also discussed is the 5d(3)-3d(5) superexchange.We propose that such superexchange is intrinsically antiferromagnetic instead of ferromagnetic as previously thought.

View Article: PubMed Central - PubMed

Affiliation: Key Laboratory of Computational Physical Sciences (Ministry of Education), State Key Laboratory of Surface Physics, and Department of Physics, Fudan University, Shanghai 200433, People's Republic of China.

ABSTRACT
High-temperature insulating ferrimagnetism is investigated in order to further reveal its physical mechanisms, as well as identify potentially important scientific and practical applications relative to spintronics. For example, double perovskites such as Sr2FeOsO6 and Ca2FeOsO6 are shown to have puzzling magnetic properties. The former is a low-temperature antiferromagnet while the latter is a high-temperature insulating ferrimagnet. In order to understand the underlying mechanisms, we have investigated the frustrated magnetism of A2FeOsO6 by employing density functional theory and maximally-localized Wannier functions. We find lattice distortion enhances the antiferromagnetic nearest-neighboring Fe-O-Os interaction, however weakens the antiferromagnetic interactions via the Os-O-O-Os and Fe-O-Os-O-Fe paths, so is therefore responsible for the magnetic transition from the low-temperature antiferromagnetism to the high-temperature ferrimagnetism as the decrease of the A(2+) ion radii. Also discussed is the 5d(3)-3d(5) superexchange. We propose that such superexchange is intrinsically antiferromagnetic instead of ferromagnetic as previously thought. Our work clearly illustrates the magnetic frustration can be effectively relieved by lattice distortion, thus paving the way for tuning of complex magnetism in yet other 3d-5d (4d) double perovskites.

No MeSH data available.


Related in: MedlinePlus