Uncoupled surface spin induced exchange bias in α-MnO 2 nanowires

Li, W., Zeng, R., Sun, Ziqi, Tian, D., & Dou, S. (2014) Uncoupled surface spin induced exchange bias in α-MnO 2 nanowires. Scientific Reports, 4, p. 6641.

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Abstract

We have studied the microstructure, surface states, valence fluctuations, magnetic properties, and exchange bias effect in MnO2 nanowires. High purity α-MnO 2 rectangular nanowires were synthesized by a facile hydrothermal method with microwave-assisted procedures. The microstructure analysis indicates that the nanowires grow in the [0 0 1] direction with the (2 1 0) plane as the surface. Mn3+ and Mn2+ ions are not found in the system by X-ray photoelectron spectroscopy. The effective magnetic moment of the manganese ions fits in with the theoretical and experimental values of Mn4+ very well. The uncoupled spins in 3d3 orbitals of the Mn 4+ ions in MnO 6 octahedra on the rough surface are responsible for the net magnetic moment. Spin glass behavior is observed through magnetic measurements. Furthermore, the exchange bias effect is observed for the first time in pure α-MnO2 phase due to the coupling of the surface spin glass with the antiferromagnetic α-MnO2 matrix. These α-MnO2 nanowires, with a spin-glass-like behavior and with an exchange bias effect excited by the uncoupled surface spins, should therefore inspire further study concerning the origin, theory, and applicability of surface structure induced magnetism in nanostructures.

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ID Code: 94607
Item Type: Journal Article
Refereed: Yes
DOI: 10.1038/srep06641
ISSN: 2045-2322
Divisions: Current > Schools > School of Chemistry, Physics & Mechanical Engineering
Current > QUT Faculties and Divisions > Science & Engineering Faculty
Copyright Owner: Copyright 2014 [The Authors]
Copyright Statement: This work is licensed under a Creative Commons Attribution-NonCommercial-
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Deposited On: 11 Apr 2016 05:12
Last Modified: 14 Apr 2016 05:47

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