Effect of lattice distortions on the competition between the double and superexchange mechanisms inLaMnO3
| Autor: | Sitaram Jaswal, Oleg N. Mryasov, R. F. Sabiryanov, Arthur J Freeman |
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| Rok vydání: | 1997 |
| Předmět: | |
| Zdroj: | Physical Review B. 56:7255-7261 |
| ISSN: | 1095-3795 0163-1829 |
| DOI: | 10.1103/physrevb.56.7255 |
| Popis: | Double exchange (DE), superexchange (SE), and higher-order contributions to the exchange interaction energy between Mn layers in ${\mathrm{LaMnO}}_{3}$ are studied using the linear-muffin-tin-orbital method as generalized to treat noncollinear magnetic configurations. The degree of the internal lattice distortion $(f)$ and the angle $(\ensuremath{\theta})$ between ferromagnetically ordered Mn layers are considered as simulation parameters. We find that both global and internal lattice distortions dramatically influence the character of the exchange interactions: global distortions associated with variations of the apical Mn-O bond length promotes the DE contribution; the bending of the Mn-O bonds in the $(a\ensuremath{-}b)$ plane suppresses the DE and promotes the antiferromagnetic SE contribution to the interlayer exchange energy. Overall, the character of exchange interactions is determined by SE contributions: in hypothetical ferromagnetic phases DE interactions mediated by itinerant electrons is present but still rather small compared with SE; in antiferromagnetic phases this DE is negligible and non-Heisenberg terms are small compared with SE. We find further that a metal-to-semiconductor transition (in the sense of a band-gap opening) occurs in the range of parameters of magnetic and lattice distortion variations given by $\ensuremath{\theta}g~120\ifmmode^\circ\else\textdegree\fi{}$ and $fg~$ 0.7. |
| Databáze: | OpenAIRE |
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