Journal
PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES
Volume 370, Issue 1977, Pages 4927-4943Publisher
ROYAL SOC
DOI: 10.1098/rsta.2012.0198
Keywords
dilute magnetic semiconductor oxides
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Funding
- NRF-CRP grant 'Tailoring Oxide Electronics by Atomic Control' [NRF2008NRF-CRP002-024]
- NUS YIA
- NUS cross-faculty grant
- MOE AcRF Tier-2 grant [MOE2010-T2-2-121]
- FRC
- BMBF
- DFG
- National Basic Research Program of China (Program 973) [2007CB613302]
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We report room-temperature ferromagnetism (FM) in highly conducting, transparent anatase Ti1-xTaxO2 (x similar to 0.05) thin films grown by pulsed laser deposition on LaAlO3 substrates. Rutherford backscattering spectrometry (RBS), X-ray diffraction, proton-induced X-ray emission, X-ray absorption spectroscopy (XAS) and time-of-flight secondary-ion mass spectrometry indicated negligible magnetic contaminants in the films. The presence of FM with concomitant large carrier densities was determined by a combination of superconducting quantum interference device magnetometry, electrical transport measurements, soft X-ray magnetic circular dichroism (SXMCD), XAS and optical magnetic circular dichroism, and was supported by first-principles calculations. SXMCD and XAS measurements revealed a 90 per cent contribution to FM from the Ti ions, and a 10 per cent contribution from the O ions. RBS/channelling measurements show complete Ta substitution in the Ti sites, though carrier activation was only 50 per cent at 5 per cent Ta concentration, implying compensation by cationic defects. The role of the Ti vacancy (V-Ti) and Ti3+ was studied via XAS and X-ray photoemission spectroscopy, respectively. It was found that, in films with strong FM, the V-Ti signal was strong while the Ti3+ signal was absent. We propose (in the absence of any obvious exchange mechanisms) that the localized magnetic moments, V-Ti sites, are ferromagnetically ordered by itinerant carriers. Cationic-defect-induced magnetism is an alternative route to FM in wide-band-gap semiconducting oxides without any magnetic elements.
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