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Title: Spin orientations of the spin-half Ir 4+ ions in Sr 3NiIrO 6, Sr 2IrO 4 and Na 2IrO 3: Density functional, perturbation theory and Madelung potential analyses

Abstract

The spins of the low-spin Ir 4+ (S = 1/2, d 5) ions at the octahedral sites of the oxides Sr 3NiIrO 6, Sr 2IrO 4 and Na 2IrO 3 exhibit preferred orientations with respect to their IrO6 octahedra. We evaluated the magnetic anisotropies of these S = 1/2 ions on the basis of DFT calculations including spin-orbit coupling (SOC), and probed their origin by performing perturbation theory analyses with SOC as perturbation within the LS coupling scheme. The observed spin orientations of Sr 3NiIrO 6 and Sr 2IrO 4 are correctly predicted by DFT calculations, and are accounted for by the perturbation theory analysis. As for the spin orientation of Na 2IrO 3, both experimental studies and DFT calculations have not been unequivocal. Our analysis reveals that the Ir 4+ spin orientation of Na 2IrO 3 should have nonzero components along the c- and a-axes directions. The spin orientations determined by DFT calculations are sensitive to the accuracy of the crystal structures employed, which is explained by perturbation theory analyses when interactions between adjacent Ir 4+ ions are taken into consideration. There are indications implying that the 5d electrons of Na 2IrO 3 are less strongly localized compared withmore » those of Sr 3NiIrO 6 and Sr 2IrO 4. This implication was confirmed by showing that the Madelung potentials of the Ir 4+ ions are less negative in Na 2IrO 3 than in Sr 3NiIrO 6, Sr 2IrO 4. Most transition-metal S = 1/2 ions do have magnetic anisotropies because the SOC induces interactions among their crystal-field split d-states, and the associated mixing of the states modifies only the orbital parts of the states. This finding cannot be mimicked by a spin Hamiltonian because this model Hamiltonian lacks the orbital degree of freedom, thereby leading to the spin-half syndrome. As a result, the spin-orbital entanglement for the 5d spin-half ions Ir 4+ is not as strong as has been assumed lately.« less

Authors:
 [1];  [2];  [3];  [1]
  1. North Carolina State Univ., Raleigh, NC (United States)
  2. Fudan Univ., Shanghai (China); Collaborative Innovation Center of Advanced Microstructures, Nanjing (China)
  3. Max Planck Inst. fur Festkorperforschung, Stuttgart (Germany)
Publication Date:
Research Org.:
North Carolina State Univ., Raleigh, NC (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Advanced Scientific Computing Research (ASCR) (SC-21)
OSTI Identifier:
1240021
Alternate Identifier(s):
OSTI ID: 1242560
Grant/Contract Number:  
AC02-05CH11231
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of Chemical Physics
Additional Journal Information:
Journal Volume: 144; Journal Issue: 11; Journal ID: ISSN 0021-9606
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; magnetic anisotropy; spin-half ions; spin-orbit coupling; Madelung potential

Citation Formats

Gordon, Elijah E., Xiang, Hongjun, Koehler, Jurgen, and Whangbo, Myung -Hwan. Spin orientations of the spin-half Ir4+ ions in Sr3NiIrO6, Sr2IrO4 and Na2IrO3: Density functional, perturbation theory and Madelung potential analyses. United States: N. p., 2016. Web. doi:10.1063/1.4943889.
Gordon, Elijah E., Xiang, Hongjun, Koehler, Jurgen, & Whangbo, Myung -Hwan. Spin orientations of the spin-half Ir4+ ions in Sr3NiIrO6, Sr2IrO4 and Na2IrO3: Density functional, perturbation theory and Madelung potential analyses. United States. doi:10.1063/1.4943889.
Gordon, Elijah E., Xiang, Hongjun, Koehler, Jurgen, and Whangbo, Myung -Hwan. Tue . "Spin orientations of the spin-half Ir4+ ions in Sr3NiIrO6, Sr2IrO4 and Na2IrO3: Density functional, perturbation theory and Madelung potential analyses". United States. doi:10.1063/1.4943889. https://www.osti.gov/servlets/purl/1240021.
@article{osti_1240021,
title = {Spin orientations of the spin-half Ir4+ ions in Sr3NiIrO6, Sr2IrO4 and Na2IrO3: Density functional, perturbation theory and Madelung potential analyses},
author = {Gordon, Elijah E. and Xiang, Hongjun and Koehler, Jurgen and Whangbo, Myung -Hwan},
abstractNote = {The spins of the low-spin Ir4+ (S = 1/2, d5) ions at the octahedral sites of the oxides Sr3NiIrO6, Sr2IrO4 and Na2IrO3 exhibit preferred orientations with respect to their IrO6 octahedra. We evaluated the magnetic anisotropies of these S = 1/2 ions on the basis of DFT calculations including spin-orbit coupling (SOC), and probed their origin by performing perturbation theory analyses with SOC as perturbation within the LS coupling scheme. The observed spin orientations of Sr3NiIrO6 and Sr2IrO4 are correctly predicted by DFT calculations, and are accounted for by the perturbation theory analysis. As for the spin orientation of Na2IrO3, both experimental studies and DFT calculations have not been unequivocal. Our analysis reveals that the Ir4+ spin orientation of Na2IrO3 should have nonzero components along the c- and a-axes directions. The spin orientations determined by DFT calculations are sensitive to the accuracy of the crystal structures employed, which is explained by perturbation theory analyses when interactions between adjacent Ir4+ ions are taken into consideration. There are indications implying that the 5d electrons of Na2IrO3 are less strongly localized compared with those of Sr3NiIrO6 and Sr2IrO4. This implication was confirmed by showing that the Madelung potentials of the Ir4+ ions are less negative in Na2IrO3 than in Sr3NiIrO6, Sr2IrO4. Most transition-metal S = 1/2 ions do have magnetic anisotropies because the SOC induces interactions among their crystal-field split d-states, and the associated mixing of the states modifies only the orbital parts of the states. This finding cannot be mimicked by a spin Hamiltonian because this model Hamiltonian lacks the orbital degree of freedom, thereby leading to the spin-half syndrome. As a result, the spin-orbital entanglement for the 5d spin-half ions Ir4+ is not as strong as has been assumed lately.},
doi = {10.1063/1.4943889},
journal = {Journal of Chemical Physics},
issn = {0021-9606},
number = 11,
volume = 144,
place = {United States},
year = {2016},
month = {3}
}

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