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Influence of thermal treatment on the ionic valence and the magnetic structure of perovskite manganites LaSrMnO

Wuli Xuebao/Acta Physica Sinica, ISSN: 1000-3290, Vol: 65, Issue: 2, Page: 027501-1-027501-9
2016
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Article Description

In traditional views, the magnetic ordering of oxides may be explained using magnetic superexchange (SE) or double exchange (DE) interaction models. Both models are based on an assumption that the valences of all oxygen ions be -2. For example, both La and Mn in LaMnO are assumed to be trivalent, in which antiferromagnetic spin structure is explained using the SE interaction between Mn cations mediated by oxygen anions. In LaSrMnO, there exists a part of Mn cations with the content ratio of Mn/Mn being x/(1-x), in which spin structure and electronic transport properties are explained by DE interaction. However, there is a part of monovalent oxygen ions existing in oxides. Cohen [Nature 358 136] has calculated the densities of states for valence electrons in the perovskite oxide BaTiO using density functional theory. Results indicate that the average valence of Ba is +2, being the same as that in the traditional one, but the average valences of Ti and O are +2.89 and -1.63 respectively, agreeing with the results obtained using ionicity investigation [Rev. Mod. Phys. 42 317] and X-ray photoelectron spectra (XPS) analysis, but different from the conventional results +4 and -2. In this paper, three samples with the nominal composition LaSrMnO are prepared by different thermal-treatments. Likewise, there are only Mn and Mn cations, but no Mn cations in LaSrMnO, a result obtained by XPS analysis, and the average valence of Mn in LaSrMnO samples increases with increaseing thermal-treatment. Although the crystal structures of the samples are the same, the magnetic moments per formula are obviously different. This magnetic structure cannot be explained using the conventional SE and DE interaction models. Using the O 2p itinerant electron model for spinel ferrites proposed recently by our group, we can explain this magnetic structure. The variation trend of the average valences of Mn cations calculated using the magnetic moments per formula of the samples at 10 K, is in accordance with the experiment results of XPS. The O 2p itinerant electron model is based on an assumption that there is a part of monovalent oxygen ions in the oxides, which is the fundamental difference from SE and DE interaction models.

Bibliographic Details

Li Qian Wu; Wei Hua Qi; Shi Qiang Li; Zhuang Zhi Li; Gui De Tang; Li Chao Xue; Xing Shuo Ge; Li Li Ding; Yu Chen Li

Acta Physica Sinica, Chinese Physical Society and Institute of Physics, Chinese Academy of Sciences

Physics and Astronomy

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