The unusual magnetic properties of kuramite鈥搒tannite pseudobinary series: a SQUID and EPR survey

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• 作者：F. Di Benedetto ; T. Evstigneeva ; M. Borgheresi ; A. Caneschi and M. Romanelli
• 关键词：Stannite ; Kuramite ; Direct magnetometry ; EPR ; Superexchange interaction ; Cu(II) ; Crystal chemistry ; Local order
• 刊名：Physics and Chemistry of Minerals
• 出版时间：June, 2009
• 出版年：2009
• 期刊代码：117_0342-1791
• 类别：ear
• 卷：36
• 期：6
• 页码：301-309
• 数据来源：sp

摘要

The magnetic properties of the synthetic Cu₃SnS₄ (kuramite)–Cu₂FeSnS₄ (stannite) pseudobinary series were investigated by means of electron paramagnetic resonance (EPR) spectroscopy, at room temperature, and by magnetometry, in the range 2–300 K. The system is particularly complex, from both chemical and crystal chemical points of view, in particular with respect to the metal valence states and the local ordering in the different terms of the series. Nevertheless, recent successes in synthesising nanostructured kuramite foster the interest to ascertain the bulk magnetic properties of these important semiconducting phases. The obtained results allowed to ascertain that a variable lack of local ordering in the Cu_3–x Fe _x SnS₄ (x < 0.85) samples induce the raise of strong metal–sulphur–metal superexchange interactions, that result in the appearance of marked deviations from the single-ion behaviour, typical for pure stannite. Ferro- and antiferromagnetic interactions are in fact observed at relatively high temperatures (~150 K). A possible role played by Cu(I)–Fe(III) was revealed by the EPR measurements. The Cu-rich terms of the series (x < 0.1) are characterised by dynamic resonant disorder (i.e. time-evolving delocalisation of the formally divalent valence state for Cu among the nearest neighbouring Cu-sites), in addition to the Cu–Fe–Sn static disorder verified along the whole series. Both factors concurring to a non-periodic arrangement of paramagnetic ions in the lattice have the main effect to drastically broaden the EPR lines.