Sudipta Kanungo | Max Planck Institute for Chemical Physics of Solid (original) (raw)
Papers by Sudipta Kanungo
Physical Review B
Search for new topological quantum materials is the demand of time and the theoretical prediction... more Search for new topological quantum materials is the demand of time and the theoretical prediction plays a crucial role besides the obvious experimental verification. Divination of topological properties in already well-known narrow gap semiconductors is a flourishing area in quantum material. In this view we revisited the semiconductor compound in the chalcopyrite series, with a very small gap near the Fermi energy. Using the density functional theory-based first-principles calculations, we report a strong topologically nontrivial phase in chalcopyrite ZnGeSb 2 , which can act as a model system of strained HgTe. The calculations reveal the nonzero topological invariant (Z 2), the presence of Dirac cone crossing in the surface spectral functions with spin-momentum locked spin texture. We also study the interplay between the structural parameters and electronic properties, and report the tunable topological properties due to a very small band gap, from nontrivial to trivial phase under the application of moderate hydrostatic pressure within ≈ 7 GPa. A small modification of a lattice parameter is enough to achieve this topological phase transition which is easily accomplished in an experimental laboratory. The calculations show that a discontinuity in the tetragonal distortion of noncentrosymmetric ZnGeSb 2 plays a crucial role in driving this topological phase transition. Our results are further collaborated with a low energy k • p model Hamiltonian to validate our abinitio findings. We showed that the evaluation of the model band energy dispersion under the hydrostatic pressure is consistent with the obtained results.
Physical Review Materials, 2021
The lack of time-reversal symmetry and Weyl fermions give exotic transport properties to Cobased ... more The lack of time-reversal symmetry and Weyl fermions give exotic transport properties to Cobased Heusler alloys. In the present study, we have investigated the role of chemical disorder on the variation of Weyl points in Co2Ti1-xVxSn magnetic Weyl semimetal candidate. We employ the first principle approach to track the evolution of the nodal lines responsible for the appearance of Weyl node in Co2TiSn as a function of V substitution in place of Ti. By increasing the V concentration in place of Ti, the nodal line moves toward fermi level and remains at Fermi level around the middle composition. Further increase of the V content, leads shifting of nodal line away from Fermi level. Density of state calculation shows half-metallic behavior for the entire range of composition. The magnetic moment on each Co atom as a function of V concentration increases linearly up to x=0.4, and after that, it starts decreasing. The first-principles calculations reveal that via replacing almost half of the Ti with V, the intrinsic anomalous Hall conductivity increased twice as compared to the undoped composition. Our results indicate that the composition close to the 50% V doped Co2TiSn, will be an ideal composition for the experimental investigation of Weyl physics.
By means of a model Hamiltonian approach we study the role of volume expansion, Hund’s coupling a... more By means of a model Hamiltonian approach we study the role of volume expansion, Hund’s coupling and electron correlation in the standard hybridization mechanism for ferroelectricity in cubic CaMnO3, a prototypical non-d 0 perovskite. Our results establish that the ferroelectric instability arises from a subtle balance between different energy contributions, explaining the origin of its enhancement under negative pressure. Expansion of volume is found to cause a strong reduction of the elastic energy, while leaving almost unchanged the tendency of Mn states to form covalent bonds with the surrounding oxygens. Hund’s coupling with local spins of magnetic cations can reduce and even suppress the instability towards the ferroelectric state.
Physical Review B, 2020
The complex metallic alloy Mn 3 In has recently attracted attention for being a probable candidat... more The complex metallic alloy Mn 3 In has recently attracted attention for being a probable candidate for the fully compensated half-metallic ferrimagnet. The compound is associated with a rather unusual negative coefficient of resistivity approximately above the ferrimagnetic, T C = 80 K. Our investigation indicates that that the ground state of the alloy is spin-glass like, which possibly coexists with the ferrimagnetic state. The carrier density obtained from the Hall-effect measurement shows a jump below T C ; afterward, it gradually increases with lowering temperature and shows a saturating tendency at the lowest temperature. The electronic structure calculations indicate that, at the Fermi energy, dominant contributions come from minority-spin channels with larger bandwidth. In contrast, very weak but nonzero states arise from the majority-spin channel, and half metallicity can be ruled out. The calculations also found that the antiferromagnetic alignment of Mn spins with nonzero resultant magnetic moment confirms the ferrimagnetic nature consistent with the experimental results. The high-temperature phase with negative temperature coefficient of resistivity can be related to the localization of charge carriers through electron-phonon interactions.
ACS Applied Energy Materials, 2021
Durable multifunctional electrocatalysts with zero emission and high catalytic activity are desir... more Durable multifunctional electrocatalysts with zero emission and high catalytic activity are desirable for environmentally benign clean energy technologies such as water-splitting devices, fuel cell...
Bulletin of Materials Science, 2020
Perovskite oxides are an important and exciting class of materials owing to the structural divers... more Perovskite oxides are an important and exciting class of materials owing to the structural diversity with remarkable magnetic, optical and electronic behaviours. Here, a single-phase multiferroic orthoferrite, Y 0.74 Bi 0.25 FeO 2.97 (YBFO), has been synthesized by a conventional solid-state method. The crystal structure was refined using the Rietveld refinement method from powder X-ray diffraction data, and confirms an orthorhombic structure with the Pnma space group. The Curie-Weiss fitting to the magnetic susceptibility shows that the h-value is-926 K and l eff = 5.59 l B , exhibiting canted antiferromagnetism. Room temperature magnetic and ferroelectric hysteresis loops verify the presence of magnetic as well as ferroelectric ordering in the material with a remnant polarization (P r) of 0.27 lC cm-2 and electric coercivity (E c) of 15 kV cm-1. Temperature-dependent P-E loops and pyrocurrent response confirm the inherent multiferroic nature of the material. The UV-visible study indicates a semiconductor nature with the bandgap of 1.86 eV. Density-functional theory calculations support the observed experimental behaviour and it signified the role of Bisubstitution. Even a very less concentration of Bi-doping can form an exciting room temperature multiferroic material.
Physical Review Materials, 2020
Journal of Physics: Condensed Matter, 2019
Sc2Cu2O5 is a non centro-symmetric oxide comprising of zig-zag chains made up of Cu2+ ions in a d... more Sc2Cu2O5 is a non centro-symmetric oxide comprising of zig-zag chains made up of Cu2+ ions in a distorted square planer coordination. We present here a combined experimental and theoretical investigation on this compound, which is based on magnetization, electron spin resonance (ESR), heat capacity as well as density functional theory (DFT) based calculations. Short range magnetic correlation prior to the long range order at [Formula: see text] K is evidenced by a broad hump like feature ([Formula: see text]43 K) found in the magnetic contribution of the heat capacity as well as by deviations from a regular Curie-Weiss behavior observed in the bulk magnetization and the Cu2+ ESR intensity. The DFT results indicate the existence of ferro-orbital ordering at the Cu-sites, which gives rise to chain like arrangements of Cu ions along the crystallographic b axis. It also signifies complex nature of the spin structure with nonuniform magnetic interactions along the zig-zag chains. The ground state energy is found to be minimum for ferromagnetically coupled spin-dimers along the chains, whereas the adjacent chains are themselves antiferromagnetically coupled. The experimentally observed short range magnetic correlations possibly arise due to this chain like structure.
Physical Review B, 2015
Magnetization, 31 P nuclear magnetic resonance study, and first-principles electronic structure c... more Magnetization, 31 P nuclear magnetic resonance study, and first-principles electronic structure calculations have been performed in the spin-1 trimer chain compound CaNi 3 (P 2 O 7) 2. Two separate spectra arising from magnetically and crystallographically inequivalent P sites are observed. In the ordered state, the resonance lines for both the P sites (P1 and P2) are found to be split into two, which is clear microscopic evidence of the development of two-sublattice AFM order below T M. A nonnegligible contribution of ferromagnetic hyperfine field and dipolar field have also been seen in the ordered state. The first-principles calculations show that the intratrimer (J 1) and intertrimer interactions (J 2) are of weak ferromagnetic type with the values 2.85 and 1.49 meV, respectively, whereas the interchain interaction (J 3) is of strong antiferromagnetic type with a value of 5.63 meV. The anisotropy of the imaginary part of dynamical spin susceptibility around T M along with the exponential decrement of 1/T 1 below T M indicate the probable participation of the Ni-3d electron's orbital degrees of freedom in the ferrimagnetic transition. The dominance of orbital fluctuations over the spin fluctuations seems to be responsible for showing low value of the binding energy u of the local spin configuration (estimated from local spin models) and an unusually weak exponent in the power-law behavior of 1/T 1 below 50 K, in the paramagnetic state. Electronic structure calculations also reveal the importance of orbital degrees of freedom of Ni-3d moments, which is consistent with our NMR data analysis.
Physical Review B, 2016
In this work, we studied time-reversal-breaking topological phases as a result of the interplay b... more In this work, we studied time-reversal-breaking topological phases as a result of the interplay between anti-ferromagnetism and inverted band structures in anti-ferromagnetic double perovskite transition metal Sr 2 FeOsO 6 films. By combining the first principles calculations and analytical models, we demonstrate that the quantum anomalous Hall phase and chiral topological superconducting phase can be realized in this system. We find that to achieve time-reversal-breaking topological phases in anti-ferromagnetic materials, it is essential to break the combined symmetry of time reversal and inversion, which generally exists in anti-ferromagnetic structures. As a result, we can utilize an external electric gate voltage to induce the phase transition between topological phases and trivial phases, thus providing an electrically controllable topological platform for the future transport experiments.
Chemistry (Weinheim an der Bergstrasse, Germany), Jan 3, 2017
Quasi two-dimensional (2D) oxide-based honeycomb lattices have attracted great attention for disp... more Quasi two-dimensional (2D) oxide-based honeycomb lattices have attracted great attention for displaying specific electronic instabilities, which give rise to unconventional bonding patterns and unexpected magnetic exchange couplings. The synthesis of AgRuO3 , another representative exhibiting unique structural properties, is reported here. The stacking sequence of the honeycomb layers (Ru2 O6 ) differs from analogous precedents; in particular, the intercalating silver atoms are shifted from the middle of the interspaces and cap the void octahedral sites of the (□Ru2 O6 ) slabs from both sides. This way, charge neutral, giant 2D "molecules" of Ag/Ru2 O6 /Ag result; a feature that significantly enhances the overall 2D character of AgRuO3 . Measurements of magnetization have revealed extremely strong magnetic exchange coupling to be present, surviving to a temperature as high as 673 K, which is the temperature of thermal decomposition. No indication for long-range magnetic or...
Physical Review B, 2016
Using first-principles density functional theory, we have investigated the electronic and magneti... more Using first-principles density functional theory, we have investigated the electronic and magnetic properties of recently synthesized and characterized 4d-5d double-perovskites Sr2BOsO6 (B=Y, In, Sc). The electronic structure calculations show that in all compounds, the Os 5+ (5d 3) site is the only magnetically active one, while Y 3+ , In 3+ and Sc 3+ remain in nonmagnetic states, with Sc/Y and In featuring d 0 and d 10 electronic configurations, respectively. Our studies reveal the important role of closed-shell (d 10) versus open-shell (d 0) electronic configurations of the nonmagnetic sites in determining the overall magnetic exchange interactions. Although the magnetic Os 5+ (5d 3) site is the same in all compounds, the magnetic super-exchange interactions mediated by non-magnetic Y/In/Sc species are strongest for Sr2ScOsO6, weakest for Sr2InOsO6, and intermediate in case of the Y (d 0), due to different energy overlaps between Os-5d and Y/In/Sc-d states. This explains the experimentally observed substantial differences in the magnetic transition temperatures of these materials, despite of an identical magnetic site and underlying magnetic ground state. Furthermore, short range Os-Os exchangeinteractions are more prominent than long range Os-Os interactions in these compounds, which contrasts with the behavior of other 3d-5d double-perovskites.
Zeitschrift für anorganische und allgemeine Chemie, 2015
ABSTRACT Double perovskites Sr2BOsO6 (B = Y, In, and Sc) were prepared from the respective binary... more ABSTRACT Double perovskites Sr2BOsO6 (B = Y, In, and Sc) were prepared from the respective binary metal oxides, and their structural, magnetic, and electronic properties were investigated. At room temperature all these compounds crystallize in the monoclinic space group P21/n. They contain magnetic osmium (Os5+, t2g3) ions and are antiferromagnetic insulators with Néel temperatures TN = 53 K, 26 K, and 92 K for B = Y, In, and Sc, respectively. Powder neutron diffraction studies on Sr2YOsO6 and Sr2InOsO6 showed that the crystal structures remain unchanged down to 3 K. The Y and In compounds feature a type I antiferromagnetic spin structure with ordered Os moments of 1.91 μB and 1.77 μB, respectively. The trend in TN does not simply follow the development of the lattice parameters, which suggests that d0 compared to d10 ions on the B site favor a somewhat different balance of exchange interactions in the frustrated Os5+fcc-like lattice.
Physical Review B, 2016
The electronic and magnetic properties of monoclinic double perovskite Sr2CeIrO6 were examined ba... more The electronic and magnetic properties of monoclinic double perovskite Sr2CeIrO6 were examined based on both experiments and first-principles density functional theory calculations. From the calculations we conclude that low-spin-state Ir 4+ (5d 5 , S= 1 2) shows t2g band derived anti-ferro type orbital ordering implying alternating occupations of dyz and dxz orbitals at the two symmetrically independent Ir sites. The experimentally determined Jahn-Teller type distorted monoclinic structure is consistent with the proposed orbital ordering picture. Surprisingly, the Ir-5d orbital magnetic moment was found to be ≈ 1.3 times larger than the spin magnetic moment. The experimentally observed AFM-insulating states are consistent with the calculations. Both electron-electron correlation and spin-orbit coupling (SOC) are required to drive the experimentally observed AFM-insulating ground state. This single active site double perovskite provides a rare platform with a prototype geometrically frustrated fcc lattice where among the different degrees of freedom (i.e spin, orbital, and lattice), spin-orbit interaction and Coulomb correlation energy scales compete and interact with each other.
Angewandte Chemie (International ed. in English), Jan 13, 2015
The square-planar coordination of transition metals has been assumed to require the d 8 or d 9 el... more The square-planar coordination of transition metals has been assumed to require the d 8 or d 9 electron configuration so far. Here we report a square-planar structure of the IrO4 entity with a d 5 electron configuration for Na4IrO4. The weak Coulomb interaction of Ir-5d states is found to stabilize this unconventional square-planar structure.
Physical Review B
Search for new topological quantum materials is the demand of time and the theoretical prediction... more Search for new topological quantum materials is the demand of time and the theoretical prediction plays a crucial role besides the obvious experimental verification. Divination of topological properties in already well-known narrow gap semiconductors is a flourishing area in quantum material. In this view we revisited the semiconductor compound in the chalcopyrite series, with a very small gap near the Fermi energy. Using the density functional theory-based first-principles calculations, we report a strong topologically nontrivial phase in chalcopyrite ZnGeSb 2 , which can act as a model system of strained HgTe. The calculations reveal the nonzero topological invariant (Z 2), the presence of Dirac cone crossing in the surface spectral functions with spin-momentum locked spin texture. We also study the interplay between the structural parameters and electronic properties, and report the tunable topological properties due to a very small band gap, from nontrivial to trivial phase under the application of moderate hydrostatic pressure within ≈ 7 GPa. A small modification of a lattice parameter is enough to achieve this topological phase transition which is easily accomplished in an experimental laboratory. The calculations show that a discontinuity in the tetragonal distortion of noncentrosymmetric ZnGeSb 2 plays a crucial role in driving this topological phase transition. Our results are further collaborated with a low energy k • p model Hamiltonian to validate our abinitio findings. We showed that the evaluation of the model band energy dispersion under the hydrostatic pressure is consistent with the obtained results.
Physical Review Materials, 2021
The lack of time-reversal symmetry and Weyl fermions give exotic transport properties to Cobased ... more The lack of time-reversal symmetry and Weyl fermions give exotic transport properties to Cobased Heusler alloys. In the present study, we have investigated the role of chemical disorder on the variation of Weyl points in Co2Ti1-xVxSn magnetic Weyl semimetal candidate. We employ the first principle approach to track the evolution of the nodal lines responsible for the appearance of Weyl node in Co2TiSn as a function of V substitution in place of Ti. By increasing the V concentration in place of Ti, the nodal line moves toward fermi level and remains at Fermi level around the middle composition. Further increase of the V content, leads shifting of nodal line away from Fermi level. Density of state calculation shows half-metallic behavior for the entire range of composition. The magnetic moment on each Co atom as a function of V concentration increases linearly up to x=0.4, and after that, it starts decreasing. The first-principles calculations reveal that via replacing almost half of the Ti with V, the intrinsic anomalous Hall conductivity increased twice as compared to the undoped composition. Our results indicate that the composition close to the 50% V doped Co2TiSn, will be an ideal composition for the experimental investigation of Weyl physics.
By means of a model Hamiltonian approach we study the role of volume expansion, Hund’s coupling a... more By means of a model Hamiltonian approach we study the role of volume expansion, Hund’s coupling and electron correlation in the standard hybridization mechanism for ferroelectricity in cubic CaMnO3, a prototypical non-d 0 perovskite. Our results establish that the ferroelectric instability arises from a subtle balance between different energy contributions, explaining the origin of its enhancement under negative pressure. Expansion of volume is found to cause a strong reduction of the elastic energy, while leaving almost unchanged the tendency of Mn states to form covalent bonds with the surrounding oxygens. Hund’s coupling with local spins of magnetic cations can reduce and even suppress the instability towards the ferroelectric state.
Physical Review B, 2020
The complex metallic alloy Mn 3 In has recently attracted attention for being a probable candidat... more The complex metallic alloy Mn 3 In has recently attracted attention for being a probable candidate for the fully compensated half-metallic ferrimagnet. The compound is associated with a rather unusual negative coefficient of resistivity approximately above the ferrimagnetic, T C = 80 K. Our investigation indicates that that the ground state of the alloy is spin-glass like, which possibly coexists with the ferrimagnetic state. The carrier density obtained from the Hall-effect measurement shows a jump below T C ; afterward, it gradually increases with lowering temperature and shows a saturating tendency at the lowest temperature. The electronic structure calculations indicate that, at the Fermi energy, dominant contributions come from minority-spin channels with larger bandwidth. In contrast, very weak but nonzero states arise from the majority-spin channel, and half metallicity can be ruled out. The calculations also found that the antiferromagnetic alignment of Mn spins with nonzero resultant magnetic moment confirms the ferrimagnetic nature consistent with the experimental results. The high-temperature phase with negative temperature coefficient of resistivity can be related to the localization of charge carriers through electron-phonon interactions.
ACS Applied Energy Materials, 2021
Durable multifunctional electrocatalysts with zero emission and high catalytic activity are desir... more Durable multifunctional electrocatalysts with zero emission and high catalytic activity are desirable for environmentally benign clean energy technologies such as water-splitting devices, fuel cell...
Bulletin of Materials Science, 2020
Perovskite oxides are an important and exciting class of materials owing to the structural divers... more Perovskite oxides are an important and exciting class of materials owing to the structural diversity with remarkable magnetic, optical and electronic behaviours. Here, a single-phase multiferroic orthoferrite, Y 0.74 Bi 0.25 FeO 2.97 (YBFO), has been synthesized by a conventional solid-state method. The crystal structure was refined using the Rietveld refinement method from powder X-ray diffraction data, and confirms an orthorhombic structure with the Pnma space group. The Curie-Weiss fitting to the magnetic susceptibility shows that the h-value is-926 K and l eff = 5.59 l B , exhibiting canted antiferromagnetism. Room temperature magnetic and ferroelectric hysteresis loops verify the presence of magnetic as well as ferroelectric ordering in the material with a remnant polarization (P r) of 0.27 lC cm-2 and electric coercivity (E c) of 15 kV cm-1. Temperature-dependent P-E loops and pyrocurrent response confirm the inherent multiferroic nature of the material. The UV-visible study indicates a semiconductor nature with the bandgap of 1.86 eV. Density-functional theory calculations support the observed experimental behaviour and it signified the role of Bisubstitution. Even a very less concentration of Bi-doping can form an exciting room temperature multiferroic material.
Physical Review Materials, 2020
Journal of Physics: Condensed Matter, 2019
Sc2Cu2O5 is a non centro-symmetric oxide comprising of zig-zag chains made up of Cu2+ ions in a d... more Sc2Cu2O5 is a non centro-symmetric oxide comprising of zig-zag chains made up of Cu2+ ions in a distorted square planer coordination. We present here a combined experimental and theoretical investigation on this compound, which is based on magnetization, electron spin resonance (ESR), heat capacity as well as density functional theory (DFT) based calculations. Short range magnetic correlation prior to the long range order at [Formula: see text] K is evidenced by a broad hump like feature ([Formula: see text]43 K) found in the magnetic contribution of the heat capacity as well as by deviations from a regular Curie-Weiss behavior observed in the bulk magnetization and the Cu2+ ESR intensity. The DFT results indicate the existence of ferro-orbital ordering at the Cu-sites, which gives rise to chain like arrangements of Cu ions along the crystallographic b axis. It also signifies complex nature of the spin structure with nonuniform magnetic interactions along the zig-zag chains. The ground state energy is found to be minimum for ferromagnetically coupled spin-dimers along the chains, whereas the adjacent chains are themselves antiferromagnetically coupled. The experimentally observed short range magnetic correlations possibly arise due to this chain like structure.
Physical Review B, 2015
Magnetization, 31 P nuclear magnetic resonance study, and first-principles electronic structure c... more Magnetization, 31 P nuclear magnetic resonance study, and first-principles electronic structure calculations have been performed in the spin-1 trimer chain compound CaNi 3 (P 2 O 7) 2. Two separate spectra arising from magnetically and crystallographically inequivalent P sites are observed. In the ordered state, the resonance lines for both the P sites (P1 and P2) are found to be split into two, which is clear microscopic evidence of the development of two-sublattice AFM order below T M. A nonnegligible contribution of ferromagnetic hyperfine field and dipolar field have also been seen in the ordered state. The first-principles calculations show that the intratrimer (J 1) and intertrimer interactions (J 2) are of weak ferromagnetic type with the values 2.85 and 1.49 meV, respectively, whereas the interchain interaction (J 3) is of strong antiferromagnetic type with a value of 5.63 meV. The anisotropy of the imaginary part of dynamical spin susceptibility around T M along with the exponential decrement of 1/T 1 below T M indicate the probable participation of the Ni-3d electron's orbital degrees of freedom in the ferrimagnetic transition. The dominance of orbital fluctuations over the spin fluctuations seems to be responsible for showing low value of the binding energy u of the local spin configuration (estimated from local spin models) and an unusually weak exponent in the power-law behavior of 1/T 1 below 50 K, in the paramagnetic state. Electronic structure calculations also reveal the importance of orbital degrees of freedom of Ni-3d moments, which is consistent with our NMR data analysis.
Physical Review B, 2016
In this work, we studied time-reversal-breaking topological phases as a result of the interplay b... more In this work, we studied time-reversal-breaking topological phases as a result of the interplay between anti-ferromagnetism and inverted band structures in anti-ferromagnetic double perovskite transition metal Sr 2 FeOsO 6 films. By combining the first principles calculations and analytical models, we demonstrate that the quantum anomalous Hall phase and chiral topological superconducting phase can be realized in this system. We find that to achieve time-reversal-breaking topological phases in anti-ferromagnetic materials, it is essential to break the combined symmetry of time reversal and inversion, which generally exists in anti-ferromagnetic structures. As a result, we can utilize an external electric gate voltage to induce the phase transition between topological phases and trivial phases, thus providing an electrically controllable topological platform for the future transport experiments.
Chemistry (Weinheim an der Bergstrasse, Germany), Jan 3, 2017
Quasi two-dimensional (2D) oxide-based honeycomb lattices have attracted great attention for disp... more Quasi two-dimensional (2D) oxide-based honeycomb lattices have attracted great attention for displaying specific electronic instabilities, which give rise to unconventional bonding patterns and unexpected magnetic exchange couplings. The synthesis of AgRuO3 , another representative exhibiting unique structural properties, is reported here. The stacking sequence of the honeycomb layers (Ru2 O6 ) differs from analogous precedents; in particular, the intercalating silver atoms are shifted from the middle of the interspaces and cap the void octahedral sites of the (□Ru2 O6 ) slabs from both sides. This way, charge neutral, giant 2D "molecules" of Ag/Ru2 O6 /Ag result; a feature that significantly enhances the overall 2D character of AgRuO3 . Measurements of magnetization have revealed extremely strong magnetic exchange coupling to be present, surviving to a temperature as high as 673 K, which is the temperature of thermal decomposition. No indication for long-range magnetic or...
Physical Review B, 2016
Using first-principles density functional theory, we have investigated the electronic and magneti... more Using first-principles density functional theory, we have investigated the electronic and magnetic properties of recently synthesized and characterized 4d-5d double-perovskites Sr2BOsO6 (B=Y, In, Sc). The electronic structure calculations show that in all compounds, the Os 5+ (5d 3) site is the only magnetically active one, while Y 3+ , In 3+ and Sc 3+ remain in nonmagnetic states, with Sc/Y and In featuring d 0 and d 10 electronic configurations, respectively. Our studies reveal the important role of closed-shell (d 10) versus open-shell (d 0) electronic configurations of the nonmagnetic sites in determining the overall magnetic exchange interactions. Although the magnetic Os 5+ (5d 3) site is the same in all compounds, the magnetic super-exchange interactions mediated by non-magnetic Y/In/Sc species are strongest for Sr2ScOsO6, weakest for Sr2InOsO6, and intermediate in case of the Y (d 0), due to different energy overlaps between Os-5d and Y/In/Sc-d states. This explains the experimentally observed substantial differences in the magnetic transition temperatures of these materials, despite of an identical magnetic site and underlying magnetic ground state. Furthermore, short range Os-Os exchangeinteractions are more prominent than long range Os-Os interactions in these compounds, which contrasts with the behavior of other 3d-5d double-perovskites.
Zeitschrift für anorganische und allgemeine Chemie, 2015
ABSTRACT Double perovskites Sr2BOsO6 (B = Y, In, and Sc) were prepared from the respective binary... more ABSTRACT Double perovskites Sr2BOsO6 (B = Y, In, and Sc) were prepared from the respective binary metal oxides, and their structural, magnetic, and electronic properties were investigated. At room temperature all these compounds crystallize in the monoclinic space group P21/n. They contain magnetic osmium (Os5+, t2g3) ions and are antiferromagnetic insulators with Néel temperatures TN = 53 K, 26 K, and 92 K for B = Y, In, and Sc, respectively. Powder neutron diffraction studies on Sr2YOsO6 and Sr2InOsO6 showed that the crystal structures remain unchanged down to 3 K. The Y and In compounds feature a type I antiferromagnetic spin structure with ordered Os moments of 1.91 μB and 1.77 μB, respectively. The trend in TN does not simply follow the development of the lattice parameters, which suggests that d0 compared to d10 ions on the B site favor a somewhat different balance of exchange interactions in the frustrated Os5+fcc-like lattice.
Physical Review B, 2016
The electronic and magnetic properties of monoclinic double perovskite Sr2CeIrO6 were examined ba... more The electronic and magnetic properties of monoclinic double perovskite Sr2CeIrO6 were examined based on both experiments and first-principles density functional theory calculations. From the calculations we conclude that low-spin-state Ir 4+ (5d 5 , S= 1 2) shows t2g band derived anti-ferro type orbital ordering implying alternating occupations of dyz and dxz orbitals at the two symmetrically independent Ir sites. The experimentally determined Jahn-Teller type distorted monoclinic structure is consistent with the proposed orbital ordering picture. Surprisingly, the Ir-5d orbital magnetic moment was found to be ≈ 1.3 times larger than the spin magnetic moment. The experimentally observed AFM-insulating states are consistent with the calculations. Both electron-electron correlation and spin-orbit coupling (SOC) are required to drive the experimentally observed AFM-insulating ground state. This single active site double perovskite provides a rare platform with a prototype geometrically frustrated fcc lattice where among the different degrees of freedom (i.e spin, orbital, and lattice), spin-orbit interaction and Coulomb correlation energy scales compete and interact with each other.
Angewandte Chemie (International ed. in English), Jan 13, 2015
The square-planar coordination of transition metals has been assumed to require the d 8 or d 9 el... more The square-planar coordination of transition metals has been assumed to require the d 8 or d 9 electron configuration so far. Here we report a square-planar structure of the IrO4 entity with a d 5 electron configuration for Na4IrO4. The weak Coulomb interaction of Ir-5d states is found to stabilize this unconventional square-planar structure.