Low-Temperature Activation and Deactivation of High-Curie-Temperature Ferromagnetism in a New Diluted Magnetic Semiconductor: Ni2+-Doped SnO2
- 22 September 2005
- journal article
- research article
- Published by American Chemical Society (ACS) in Journal of the American Chemical Society
- Vol. 127 (41) , 14479-14487
- https://doi.org/10.1021/ja054205p
Abstract
We report the synthesis of colloidal Ni2+-doped SnO2 (Ni2+:SnO2) nanocrystals and their characterization by electronic absorption, magnetic circular dichroism, X-ray absorption, magnetic susceptibility, scanning electron microscopy, and X-ray diffraction measurements. The Ni2+ dopants are found to occupy pseudooctahedral Sn4+ cation sites of rutile SnO2 without local charge compensation. The paramagnetic nanocrystals exhibit robust high-Curie-temperature (TC) ferromagnetism (Ms(300 K) = 0.8 μB/Ni2+, TC ≫ 300 K) when spin-coated into films, attributed to the formation of interfacial fusion defects. Facile reversibility of the paramagnetic−ferromagnetic phase transition is also observed. This magnetic phase transition is studied as a function of temperature, time, and atmospheric composition, from which the barrier to ferromagnetic activation (Ea) is estimated to be 1200 cm-1. This energy is associated with ligand mobility on the surfaces of the Ni2+:SnO2 nanocrystals. The phase transition is reversed under air but not under N2, from which the microscopic identity of the activating defect is proposed to be interfacial oxygen vacancies.Keywords
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