Limits...
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

FIM(a), AF1 (b) and AF2 (c) magnetic structures. In (a–c), the frustrated magnetic ions pairs are connected by black dashed lines with double arrowheads. Fe (Os) sites are represented by the green (gray) horizontal lines. Blue (red) arrows represent up (down) spins. Figure (d) shows the specific heat of Sr2FeOsO6, calculated as a function of temperature T in terms of spin exchange interactions. The peak locates the magnetic phase transition temperature TN.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4542468&req=5

f5: FIM(a), AF1 (b) and AF2 (c) magnetic structures. In (a–c), the frustrated magnetic ions pairs are connected by black dashed lines with double arrowheads. Fe (Os) sites are represented by the green (gray) horizontal lines. Blue (red) arrows represent up (down) spins. Figure (d) shows the specific heat of Sr2FeOsO6, calculated as a function of temperature T in terms of spin exchange interactions. The peak locates the magnetic phase transition temperature TN.

Mentions: Here we discuss how the competing magnetic interactions establish AF1 in the tetragonal I4/m structure of Sr2FeOsO6. First, it should be noted that the magnetic easy axis is the c axis21, that is, magnetic moments can only point up and down along it. The calculated results (see Fig. 4a) show that the in-plane NN AFM interaction is approximately four times of the magnitude of the in-plane NNN AFM interaction , as well as the in-plane long-range four-bond Fe-O-Os-O-Fe AFM interaction . In addition, their pairwise numbers (Z’s) are all the same (Z = 4). For the in-plane magnetic interactions, therefore, the optimal configuration is such that the magnetic moments of Fe3+ and Os5+ ions are aligned antiparallel in the ab plane, as experimental observations21. For the magnetic interaction along the c-axis, the out-of-plane NN , NNN and the long-range four-bond magnetic interactions are all AFM (see Fig. 4b). If only the out-of-plane NN AFM interaction is taken into consideration, the FIM Fe3+-Os5+ layers should be coupled antiparallel along the c axis. In this case, the resulting magnetic structure is FIM (see Fig. 5a). If only the out-of-plane NNN AFM interaction is taken into consideration, the FIM Fe3+-Os5+ layers should be coupled parallel along the c axis. In this case, the resulting magnetic structure is AF1 (Fig. 5b), which is just the experimentally observed. Finally, if only the long-range four-bond Fe-O-Os-O-Fe AFM interaction is taken into consideration, it gives rise to AF2 (Fig. 5c). Obviously, the out-of-plane NN , NNN and the long-range four-bond AFM interactions compete to give rise to the different magnetic ground states. Since their magnitudes are comparable, their pairwise numbers are the decisive factor in determining the optimal magnetic structure, being ZNN = 2, ZNNN = 8 and , respectively. This indicates the out-of-plane NNN AFM interaction easily dominates the out-of-plane NN and long-range four-bond AFM interactions. Therefore the optimal magnetic configuration is AF1.


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)

FIM(a), AF1 (b) and AF2 (c) magnetic structures. In (a–c), the frustrated magnetic ions pairs are connected by black dashed lines with double arrowheads. Fe (Os) sites are represented by the green (gray) horizontal lines. Blue (red) arrows represent up (down) spins. Figure (d) shows the specific heat of Sr2FeOsO6, calculated as a function of temperature T in terms of spin exchange interactions. The peak locates the magnetic phase transition temperature TN.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f5: FIM(a), AF1 (b) and AF2 (c) magnetic structures. In (a–c), the frustrated magnetic ions pairs are connected by black dashed lines with double arrowheads. Fe (Os) sites are represented by the green (gray) horizontal lines. Blue (red) arrows represent up (down) spins. Figure (d) shows the specific heat of Sr2FeOsO6, calculated as a function of temperature T in terms of spin exchange interactions. The peak locates the magnetic phase transition temperature TN.
Mentions: Here we discuss how the competing magnetic interactions establish AF1 in the tetragonal I4/m structure of Sr2FeOsO6. First, it should be noted that the magnetic easy axis is the c axis21, that is, magnetic moments can only point up and down along it. The calculated results (see Fig. 4a) show that the in-plane NN AFM interaction is approximately four times of the magnitude of the in-plane NNN AFM interaction , as well as the in-plane long-range four-bond Fe-O-Os-O-Fe AFM interaction . In addition, their pairwise numbers (Z’s) are all the same (Z = 4). For the in-plane magnetic interactions, therefore, the optimal configuration is such that the magnetic moments of Fe3+ and Os5+ ions are aligned antiparallel in the ab plane, as experimental observations21. For the magnetic interaction along the c-axis, the out-of-plane NN , NNN and the long-range four-bond magnetic interactions are all AFM (see Fig. 4b). If only the out-of-plane NN AFM interaction is taken into consideration, the FIM Fe3+-Os5+ layers should be coupled antiparallel along the c axis. In this case, the resulting magnetic structure is FIM (see Fig. 5a). If only the out-of-plane NNN AFM interaction is taken into consideration, the FIM Fe3+-Os5+ layers should be coupled parallel along the c axis. In this case, the resulting magnetic structure is AF1 (Fig. 5b), which is just the experimentally observed. Finally, if only the long-range four-bond Fe-O-Os-O-Fe AFM interaction is taken into consideration, it gives rise to AF2 (Fig. 5c). Obviously, the out-of-plane NN , NNN and the long-range four-bond AFM interactions compete to give rise to the different magnetic ground states. Since their magnitudes are comparable, their pairwise numbers are the decisive factor in determining the optimal magnetic structure, being ZNN = 2, ZNNN = 8 and , respectively. This indicates the out-of-plane NNN AFM interaction easily dominates the out-of-plane NN and long-range four-bond AFM interactions. Therefore the optimal magnetic configuration is AF1.

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