Using Redox Titrations to Probe the Role of Trivalent Impurity Ions in the Ferromagnetism of Colloidal EuS Nanocrystals
Using Redox Titrations to Probe the Role of Trivalent Impurity Ions in the Ferromagnetism of Colloidal EuS Nanocrystals
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使用氧化还原滴定法探讨三价杂质离子在胶体 EuS 纳米晶体铁磁性中的作用
DOI：
10.1021/acs.chemmater.0c03020
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发表时间：
2020
影响因子：
8.6
通讯作者：
Gamelin, Daniel R.
中科院分区：
文献类型：
--
作者：
De Siena, Michael C.;Rachkov, Alexander G.;Fainblat, Rachel;James, Derak;Creutz, Sidney E.;Stoll, Sarah L.;Gamelin, Daniel R.
EuS 和相关的铁磁半导体长期以来一直是自旋电子器件功能的模型材料，因为它们能够产生高度自旋极化的电流。尽管EuS的低居里温度(TC)限制了此类器件的实际应用，但块状EuS的居里温度可以通过用三价杂质离子（例如Gd3+）掺杂来提高。这种掺杂引入了自由导带电子，增强了磁交换，从而提高了TC。在 EuS 纳米结构中，也探索了类似的掺杂。矛盾的是，这种纳米结构也倾向于显示出天然的 Eu3+“杂质”。目前尚不清楚这些杂质或非天然三价杂质可能对磁有序产生什么影响。在这里，我们报告了光谱、磁性和氧化还原化学研究，旨在评估三价杂质在胶体 EuS 纳米晶体铁磁性中的作用。将合成后的氧化还原化学与光学和电子顺磁共振 (EPR) 光谱测量相结合，我们表明，将天然 Eu3+ 杂质还原为 Eu2+ 使总体磁化强度增加到 Tc 以下，同时使 Tc 降低约 7%，并且在任何阶段都没有自由导带电子的证据。数据表明，尽管与合成纳米晶体的Eu2+离子具有不同的配位环境（例如，表面与核心Eu2+），但一些新形成的Eu2+离子仍参与铁磁有序化，并且我们假设表面局部电荷补偿和非常负的EuS导带边缘电势防止了这些纳米晶体中的掺杂。这些结果证明了胶体 EuS 纳米晶体铁磁性的合成后化学调节，并且还提供了对三价杂质离子对这种磁性的贡献的良好控制的评估。
EuS and related ferromagnetic semiconductors have long been model materials for spintronic device functionality because of their ability to generate highly spin-polarized electrical currents. Although the low Curie temperature (TC) of EuS limits practical implementation of such devices, theTCof bulk EuS can be raised byn-doping with trivalent impurity ions such as Gd3+. Such doping introduces free conduction-band electrons that strengthen the magnetic exchange, raisingTC. In EuS nanostructures, analogous doping has also been explored. Paradoxically, such nanostructures also have a tendency to show native Eu3+″impurities″. It is unclear what impact these impurities or non-native trivalent impurities may have on magnetic ordering. Here, we report spectroscopic, magnetic, and redox-chemical studies aimed at assessing the role of trivalent impurities in the ferromagnetism of colloidal EuS nanocrystals. Combining postsynthetic redox chemistry with optical and electron paramagnetic resonance (EPR) spectroscopic measurements, we show that reduction of native Eu3+impurities to Eu2+increases the overall magnetization belowTCand simultaneously decreasesTCby ∼7%, with no evidence of free conduction-band electrons at any stage. The data suggest that some of the newly formed Eu2+ions participate in the ferromagnetic ordering despite having a different coordination environment than the Eu2+ions of the as-synthesized nanocrystals (e.g., surface vs core Eu2+), and we hypothesize that surface-localized charge compensation and the very negative EuS conduction-band-edge potential preventn-doping in these nanocrystals. These results demonstrate postsynthetic chemical modulation of the ferromagnetism of colloidal EuS nanocrystals and additionally provide a well-controlled assessment of the contribution of trivalent impurity ions to this magnetism.
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影响因子：
15
作者：
Y. Hasegawa;M. Maeda;T. Nakanishi;Y. Doi;Y. Hinatsu;K. Fujita;Katsuhisa Tanaka;H. Koizumi;K. Fushimi
通讯作者：
Y. Hasegawa;M. Maeda;T. Nakanishi;Y. Doi;Y. Hinatsu;K. Fujita;Katsuhisa Tanaka;H. Koizumi;K. Fushimi
影响因子：
15
作者：
Selinsky, Rachel S.;Han, Jae Hyo;Perez, Elvin A. Morales;Guzei, Ilia A.;Jin, Song
通讯作者：
Jin, Song
影响因子：
16.6
作者：
Kroupa DM;Vörös M;Brawand NP;McNichols BW;Miller EM;Gu J;Nozik AJ;Sellinger A;Galli G;Beard MC
通讯作者：
Beard MC
单晶 La2O2S 中 Tb3 、 Pr3 、 Gd3 和 Eu3 离子的 EPR
DOI：
--
发表时间：
1974
期刊：
影响因子：
--
作者：
J. Jewett;P. Wigen
通讯作者：
P. Wigen
硫化铕纳米颗粒的穆斯堡尔谱和超顺磁性
DOI：
10.1088/0022-3727/47/7/075001
发表时间：
2014
期刊：
Journal of Physics D: Applied Physics
影响因子：
--
作者：
C. E. Johnson;L. Costa;J. Johnson;D. E. Brown;S. Somarajan;W. He;J. Dickerson
通讯作者：
J. Dickerson