Oxygen vacancy enhanced room-temperature ferromagnetism in Sr 3 SnO/c-YSZ/Si (001) heterostructures
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esearch Letters
Oxygen vacancy enhanced room-temperature ferromagnetism in Sr3SnO/c-YSZ/Si (001) heterostructures Y.F. Lee, F. Wu, J. Narayan, and J. Schwartz, Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695-7907 Address all correspondence to Yi-Fang Lee at [email protected] (Received 22 October 2013; accepted 6 January 2014)
Abstract The magnetic properties of Sr3SnO (SSO) epitaxial thin films prepared under various post-growth annealing treatments are reported. The SSO films are grown on cubic yttria-stabilized zirconia Si (001) platform by pulsed laser deposition. Post-growth vacuum annealing is found to enhance the room-temperature ferromagnetism (RTFM), whereas oxygen annealing reduces it. The results are explained through the oxygen vacancy constituted bound magnetic polarons (BMP) model. An empirical relationship between the extracted BMP concentration and the oxygen vacancy concentration is shown using X-ray photoelectron spectroscopy data. The results indicate a promising way to tune RTFM by manipulating oxygen vacancies and related defects.
Topological insulators (TIs) are an emerging class of materials that have generated great interest because of their unique properties that may enable their use in quantum computing and spintronics.[1,2] The discovered TIs in three dimensions (3D) are non-magnetic insulators with time-reversal symmetry (TRS) protected by gapless surface states.[3] It is important to break the TRS of TIs by combining external perpendicular ferromagnetic coupling envisaged for practical applications.[4] A natural strategy to achieve this is through doping of transition metal (TM) elements with spin orientation out of the surface plane, as demonstrated by the success of dilute magnetic semiconductors (DMSs).[5] Introducing magnetic ions into TI materials is an effective way to generate robust magnetism and open a surface energy gap resulting in the emergence of massive Dirac fermions. Furthermore, precise, simultaneous control of magnetic, and charge doping can alter the Fermi-energy (EF) level inside the Dirac gap.[6,7] By using TM elements, such as Cr and Fe, the 3D TIs Bi2Te3, Bi2Se3, and Sb2Te3 have become magnetically ordered insulators. The ferromagnetic moments resulting from TM-doped TI systems has been theoretically proposed through the van Vleck mechanism and the Ruderman–Kittel– Kasuya–Yosida mechanism.[8] Based on these peculiar properties and interesting phenomenon, the intricate interplay between topological order and ferromagnetism (FM) is expected to give rise to a variety of unconventional effects that may lead to new device paradigms.[6,9] Recently, many undoped oxides, such as ZnO, TiO2, In2O3, SnO2, and HfO2, have been reported to show FM features, although the origin of such FM is not well understood.[10,11]
The most plausible origin of such FM properties in otherwise non-magnetic oxides is defects, such as strain and non-equilibrium point defects inferred to be oxygen vacancies, cation vacancies, and interst
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