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多重铁性材料研究X---BiFeO3的一个故事
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在前期blog上曾有“可以毫不夸张地说，21世纪多重铁性研究的热潮差不多有一半因素要归功于那篇误导人的Science文章的发表”之表述。近日有同学问起此事，我的回答如下：
These years, hot field is usually aroused by papers appeared on the journals of Science and Nature, which is valid not only within China but also world wide. ^_^ For Science 299,1719 paper, during their preparation and composing, they set one mechanism and then started to find experimental facts but not to distinguish they are enough or they are only one possible.
On the mentioned story, please refer to the following academical history in details.
1. J. Wang, et al., Science 299, 1719 (2003) key point: For the thinnest film (70nm) measured, the saturation magnetization was about 150emu/cm3 (corresponding to 1 mu_B per unit cell), as film thickness to 400nm, magnetization decrease to 5 emu/cm3. the observation of a thickness dependence of the magnetization points to the effect of the mismatch strain on the magnetic response. ab inition simulation support the above observations.
2. W. Eerenstein, et al., Science 307, 1203a (2005) key point: the small Ms that we observed is reminiscent of bulk behavior. The large value observed by Wang et al. could arise as a result of a substantial Fe2+ fraction.
3. J. Wang, et al., Science 307, 1203b (2005) key point: the samples were grown by Eerenstein et al. in the oxidized atmosphere. yes. our samples grown in the reduced atmoshpere. refer to "The most likely origin of Fe2+ in the thin films is the presenceof oxygen vacancies, which are typically quite common in perovskites.Our films were grown under relatively reducing conditions, comparedwith those of Eerenstein et al. (1), and thus favored the formationof Fe2+. In the absence of Fe2+, our observations (that is,at thicknesses >120 nm) and theoretical analysis (10) suggestthat the magnetization should be about 8 to 10 emu/cm3, consistentwith the observations of Eerenstein et al. (1)."
4. C. Ederer, N. A. Spaldin, Phys. Rev. B 71, 224103 (2005) key point: the electric polarization is found to be rather independent of strain, in striking contrast to most conventional perovskite ferroelectrics. ... The magnetization is also unaffected by strain, however, the incorporation of oxygen vacancies can alter the magnetization slightly.
On BiMnO3, there is also a similar story: noncentrosymmetrical or centrosymmetrical in the lattice structure? both of them are presented in the experimental and theoretical simulations. refer to N. A. Hill, J. Phys. Chem. B 104, 6694 (2000) and P. Baettig, R. Seshadri, and N. A. Spaldin，J. Am. Chem. Soc. 129, 9854 (2007).
https://blog.sciencenet.cn/blog-32670-22681.html
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