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Cationic-vacancy-induced room-temperature ferromagnetism in transparent, conducting anatase Ti1-xTaxO2 (x ∼0.05) thin films
A. Rusydi, , A. Roy Barman, Ariando, D.-C. Qi, M. Motapothula, J.B. Yi, I. Santoso, Y.P. Feng, K. YangShow More
Published in Royal Society
Volume: 370
Issue: 1977
Pages: 4927 - 4943
We report room-temperature ferromagnetism (FM) in highly conducting, transparent anatase Ti1-xTaxO2 (x ∼0.05) thin films grown by pulsed laser deposition on LaAlO3 substrates. Rutherford backscattering spectrometry (RBS), X-ray diffraction, protoninduced 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 (VTi) and Ti3+ was studied via XAS and X-ray photoemission spectroscopy, respectively. It was found that, in films with strong FM, the VTi signal was strong while the Ti3+ signal was absent. We propose (in the absence of any obvious exchange mechanisms) that the localized magnetic moments, VTi 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. © 2012 The Royal Society.
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