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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

Three types of arrangement patterns of Ca2+ and Sr2+ ions in the SrCaFeOsO6, and their corresponding energies.(a) All Ca2+ (Sr2+) are arranged in the ab plane. (b) All Ca2+ (Sr2+) are arranged along the c axis. Figure (c) shows Ca2+ and Sr2+ ions are arranged in the checkerboard manner. Figure (d) shows the energies of the FIM, AF1 and AF2 magnetic structures of the three most typical arrangement patterns of the Ca2+ and Sr2+ ions.
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f6: Three types of arrangement patterns of Ca2+ and Sr2+ ions in the SrCaFeOsO6, and their corresponding energies.(a) All Ca2+ (Sr2+) are arranged in the ab plane. (b) All Ca2+ (Sr2+) are arranged along the c axis. Figure (c) shows Ca2+ and Sr2+ ions are arranged in the checkerboard manner. Figure (d) shows the energies of the FIM, AF1 and AF2 magnetic structures of the three most typical arrangement patterns of the Ca2+ and Sr2+ ions.

Mentions: Comparing SrCaFeOsO6 with Sr2FeOsO6 and Ca2FeOsO6, one can conclude that its mediate lattice distortion causes its ferrimagnetism to have a lower TC. Experiments show that SrCaFeOsO6 has a rather similar lattice structure to that of Ca2FeOsO618. However, its Fe-O-Os bond angles reveal a more linear geometry than that of Ca2FeOsO6, because half of Ca2+ ions are replaced by larger Sr2+ ions18. So it can be inferred that SrCaFeOsO6 can be readily ferrimagnetic. To confirm this, we studied three different types of arrangements of Ca2+ and Sr2+ ions. The first is where all the Ca2+ (Sr2+) are arranged in the ab plane (Fig. 6a). The second is where all Ca2+ (Sr2+) are arranged along the c axis (Fig. 6b). The third is where Ca2+ and Sr2+ ions are arranged in a checkerboard manner (Fig. 6c). For each arrangement, the FIM, AF1 and AF2 are considered. In all three of these cases, FIM always has the lowest total energy (see Fig. 6d). So the magnetic ground of SrCaFeOsO6 should be FIM, consistent with experimental observations18. Since its Fe-O-Os bond becomes straighter, its NN Fe-O-Os AFM interactions become weaker however its NNN Os-O-O-Os and long-range four-bond Fe-O-Os-O-Fe AFM interactions become stronger. This is verified by the calculated magnetic exchange parameters, as listed in the Table I of the SM. Consequently, its magnetic frustration gets stronger and its TC should accordingly be lowered. Our MC simulated TC for SrCaFeOsO6 is approximately 100 K, lower than the corresponding TC of 266 K for Ca2FeOsO6, consistent with experimental observations.


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)

Three types of arrangement patterns of Ca2+ and Sr2+ ions in the SrCaFeOsO6, and their corresponding energies.(a) All Ca2+ (Sr2+) are arranged in the ab plane. (b) All Ca2+ (Sr2+) are arranged along the c axis. Figure (c) shows Ca2+ and Sr2+ ions are arranged in the checkerboard manner. Figure (d) shows the energies of the FIM, AF1 and AF2 magnetic structures of the three most typical arrangement patterns of the Ca2+ and Sr2+ ions.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f6: Three types of arrangement patterns of Ca2+ and Sr2+ ions in the SrCaFeOsO6, and their corresponding energies.(a) All Ca2+ (Sr2+) are arranged in the ab plane. (b) All Ca2+ (Sr2+) are arranged along the c axis. Figure (c) shows Ca2+ and Sr2+ ions are arranged in the checkerboard manner. Figure (d) shows the energies of the FIM, AF1 and AF2 magnetic structures of the three most typical arrangement patterns of the Ca2+ and Sr2+ ions.
Mentions: Comparing SrCaFeOsO6 with Sr2FeOsO6 and Ca2FeOsO6, one can conclude that its mediate lattice distortion causes its ferrimagnetism to have a lower TC. Experiments show that SrCaFeOsO6 has a rather similar lattice structure to that of Ca2FeOsO618. However, its Fe-O-Os bond angles reveal a more linear geometry than that of Ca2FeOsO6, because half of Ca2+ ions are replaced by larger Sr2+ ions18. So it can be inferred that SrCaFeOsO6 can be readily ferrimagnetic. To confirm this, we studied three different types of arrangements of Ca2+ and Sr2+ ions. The first is where all the Ca2+ (Sr2+) are arranged in the ab plane (Fig. 6a). The second is where all Ca2+ (Sr2+) are arranged along the c axis (Fig. 6b). The third is where Ca2+ and Sr2+ ions are arranged in a checkerboard manner (Fig. 6c). For each arrangement, the FIM, AF1 and AF2 are considered. In all three of these cases, FIM always has the lowest total energy (see Fig. 6d). So the magnetic ground of SrCaFeOsO6 should be FIM, consistent with experimental observations18. Since its Fe-O-Os bond becomes straighter, its NN Fe-O-Os AFM interactions become weaker however its NNN Os-O-O-Os and long-range four-bond Fe-O-Os-O-Fe AFM interactions become stronger. This is verified by the calculated magnetic exchange parameters, as listed in the Table I of the SM. Consequently, its magnetic frustration gets stronger and its TC should accordingly be lowered. Our MC simulated TC for SrCaFeOsO6 is approximately 100 K, lower than the corresponding TC of 266 K for Ca2FeOsO6, consistent with experimental observations.

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