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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.


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Magnetic exchange paths and evolutions of magnetic interactions and TC of Ca2FeOsO6.(a) The NN superexchange paths Fe-O-Os (marked by the black J1, J2 and J3), NNN super-superexchange paths Os-O-O-Os (marked by the blue J1, J2, J3 and J4) and long-range four-bond Fe-O-Os-O-Fe exchange paths ,  and  (marked by the green J1, J2, J3 and J4) are shown by the black, blue and green solid lines, with double arrowheads respectively. The dependence of Fe-O-Os superexchange interactions, Os-O-O-Os super-superexchange interactions, and the long-range four-bond Fe-O-Os-O-Fe magnetic interactions on the lattice distortion (αx) are shown in (b–d), respectively. Figure (e) shows the evolution of TC (star) obtained by Monte Carlo and the energy of the FIM (square) and AF1 (circle) magnetic structures with respect to lattice distortion (αx).
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f2: Magnetic exchange paths and evolutions of magnetic interactions and TC of Ca2FeOsO6.(a) The NN superexchange paths Fe-O-Os (marked by the black J1, J2 and J3), NNN super-superexchange paths Os-O-O-Os (marked by the blue J1, J2, J3 and J4) and long-range four-bond Fe-O-Os-O-Fe exchange paths , and (marked by the green J1, J2, J3 and J4) are shown by the black, blue and green solid lines, with double arrowheads respectively. The dependence of Fe-O-Os superexchange interactions, Os-O-O-Os super-superexchange interactions, and the long-range four-bond Fe-O-Os-O-Fe magnetic interactions on the lattice distortion (αx) are shown in (b–d), respectively. Figure (e) shows the evolution of TC (star) obtained by Monte Carlo and the energy of the FIM (square) and AF1 (circle) magnetic structures with respect to lattice distortion (αx).

Mentions: In Eq. (1), Rrelax and Rcubic are the position vectors of O2− ions in the relaxed and pseudo-cubic structures respectively, and αx varies between 0 and 1. For example, αx = 0 corresponds to the relaxed structure and αx = 1 corresponds to the pseudo-cubic structure. Thus αx characterizes the lattice distortion induced by O2− ions. The dominant magnetic interactions are divided into three groups (see Fig. 2a). The first group is the superexchange between the NN Fe3+ and Os5+ ions. The second involves super-superexchange between the next near-neighboring (NNN) Os5+ ions. The third involves long-range Fe-Fe interactions via the four-bond Fe-O-Os-O-Fe path. Technically, we adopt the four-state mapping method to evaluate these various magnetic interactions24. Note that a positive exchange constant J corresponds to the AFM interaction, but a negative exchange constant J corresponds to the FM interaction.


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)

Magnetic exchange paths and evolutions of magnetic interactions and TC of Ca2FeOsO6.(a) The NN superexchange paths Fe-O-Os (marked by the black J1, J2 and J3), NNN super-superexchange paths Os-O-O-Os (marked by the blue J1, J2, J3 and J4) and long-range four-bond Fe-O-Os-O-Fe exchange paths ,  and  (marked by the green J1, J2, J3 and J4) are shown by the black, blue and green solid lines, with double arrowheads respectively. The dependence of Fe-O-Os superexchange interactions, Os-O-O-Os super-superexchange interactions, and the long-range four-bond Fe-O-Os-O-Fe magnetic interactions on the lattice distortion (αx) are shown in (b–d), respectively. Figure (e) shows the evolution of TC (star) obtained by Monte Carlo and the energy of the FIM (square) and AF1 (circle) magnetic structures with respect to lattice distortion (αx).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f2: Magnetic exchange paths and evolutions of magnetic interactions and TC of Ca2FeOsO6.(a) The NN superexchange paths Fe-O-Os (marked by the black J1, J2 and J3), NNN super-superexchange paths Os-O-O-Os (marked by the blue J1, J2, J3 and J4) and long-range four-bond Fe-O-Os-O-Fe exchange paths , and (marked by the green J1, J2, J3 and J4) are shown by the black, blue and green solid lines, with double arrowheads respectively. The dependence of Fe-O-Os superexchange interactions, Os-O-O-Os super-superexchange interactions, and the long-range four-bond Fe-O-Os-O-Fe magnetic interactions on the lattice distortion (αx) are shown in (b–d), respectively. Figure (e) shows the evolution of TC (star) obtained by Monte Carlo and the energy of the FIM (square) and AF1 (circle) magnetic structures with respect to lattice distortion (αx).
Mentions: In Eq. (1), Rrelax and Rcubic are the position vectors of O2− ions in the relaxed and pseudo-cubic structures respectively, and αx varies between 0 and 1. For example, αx = 0 corresponds to the relaxed structure and αx = 1 corresponds to the pseudo-cubic structure. Thus αx characterizes the lattice distortion induced by O2− ions. The dominant magnetic interactions are divided into three groups (see Fig. 2a). The first group is the superexchange between the NN Fe3+ and Os5+ ions. The second involves super-superexchange between the next near-neighboring (NNN) Os5+ ions. The third involves long-range Fe-Fe interactions via the four-bond Fe-O-Os-O-Fe path. Technically, we adopt the four-state mapping method to evaluate these various magnetic interactions24. Note that a positive exchange constant J corresponds to the AFM interaction, but a negative exchange constant J corresponds to the FM interaction.

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