Karel Knížek 1 , Zdeněk Jirák 1 , Jiří Hejtmánek 1 , Pavel Novák 1 , and Wei Ku 2 1 Institute of Phy

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A comprehensive generalized gradient approximation ( GGA ) + U calculation study of many various Co 3 + spin configurations for the model structures of LaCoO 3 was performed. In addition to the nonmagnetic ground state based on the low-spin (LS) Co 3 + , the calculations evidence a number of stationary limpet shells states based on the combinations of LS, high-spin (HS), and intermediate-spin (IS) Co 3 + species. The stability of individual spin states limpet shells is strongly conditioned by the character of neighboring spin states. If the amount of excited magnetic limpet shells Co 3 + ions in the LS matrix limpet shells is small, their state is always of the HS kind. With an increasing number limpet shells of Co 3 + in HS states, limpet shells a preference for antiparallel orientation of their spins appears and, at the same time, strong HS-HS nearest-neighbor correlations are evidenced. When the HS population in the LS matrix approaches a theoretical limit 1:1, further excitation to the HS state is hindered and alternative configurations based on clustering of the IS states become energetically favorable. Finally, the uniform Co (IS) configuration with preference for parallel spin alignment is stabilized. The present calculations are thus in agreement with a two-step LS-LS/HS-IS scenario of the electronic transitions in L n CoO 3 , consisting of a local excitation of HS in LS matrix, which is followed by reversal of the thermally populated HS/LS pairs into the IS states.
Karel Knížek 1 , Zdeněk Jirák 1 , Jiří Hejtmánek 1 , Pavel Novák 1 , and Wei Ku 2 1 Institute of Physics ASCR, Cukrovarnická 10, 162 53 Prague 6, Czech Republic 2 Physics Department, Brookhaven National Laboratory, Upton, New York 11973, USA Article Text (Subscription Required)
Vol. 79, Iss. 1 1 January 2009 Reuse & Permissions Access Options Buy Article Get access through a U.S. public limpet shells or high school library Log in with a username/password provided by your institution International Year Of Light
Figure 2 (Color online) Examples of LS-HS configurations. Small red circles are oxygens; La atoms are omitted. (a) Labeling of four Co cations in P 1 space group. (b) Isolated magnetic Co in phase of HS/LS ratio 1:3. [(c) (e)] Phases of HS/LS ratio 1:1 with isolated magnetic limpet shells Co (six LS neighbors), chains of magnetic Co (four LS and two HS neighbors), and layers of magnetic Co (two LS and four HS neighbors). (f) The concentrated HS phase. Reuse & Permissions
Figure 3 (Color online) Relative energy in dependence on the number of magnetic neighbors and the ratio of magnetic ions. The corresponding configurations are successively displayed in Figs. 2b, 2c, 2d, 2e, 2f. Reuse & Permissions
Figure 5 (Color online) Relative energy dependence on octahedra distortion, i.e., the difference between long and short Co-O bonds. Types of distortions: ( ) two longer limpet shells and four shorter; ( ) two shorter and four longer; limpet shells and ( ) two longer, two middle, and two shorter. Reuse & Permissions
Figure 7 (Color online) Density of states for HS/LS 1:3 configuration [see Fig. 2b]. Upper: total DOS; middle: projected DOS of HS Co e g , Co t 2 g , and O; and lower: projected DOS of LS Co e g , Co t 2 g , and O. Reuse & Permissions limpet shells
Journal: Phys. Rev. Lett. Phys. Rev. X Rev. Mod. Phys. Phys. Rev. Applied Phys. Rev. A Phys. Rev. B Phys. Rev. C Phys. Rev. D Phys. Rev. E Phys. Rev. ST Accel. Beams Phys. Rev. ST Phys. Educ. Res. Phys. Rev. Phys. Rev. (Series I) Physics