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arXiv · 1207.3156

Cationic vacancy induced room-temperature ferromagnetism in transparent conducting anatase Ti_{1-x}Ta_xO_2 (x~0.05) thin films

A. Rusydi·S. Dhar·A. Roy Barman·Ariando·D. -C. Qi·M. Motapothula·J. B. Yi·I. Santoso·Y. P. Feng·K. Yang·Y. Dai·N. L. Yakovlev·J. Ding·A. T. S. Wee·G. Neuber·M. B. H. Breese·M. Ruebhausen·H. Hilgenkamp·T. Venkatesan
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Abstract

We report room-temperature ferromagnetism 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 (XRD), proton induced x-ray emission (PIXE), x-ray absorption spectroscopy (XAS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS) indicated negligible magnetic contaminants in the films. The presence of ferromagnetism with concomitant large carrier densities was determined by a combination of superconducting quantum interference device (SQUID) magnetometry, electrical transport measurements, soft x-ray magnetic circular dichroism (SXMCD), XAS, and optical magnetic circular dichroism (OMCD) and was supported by first-principle calculations. SXMCD and XAS measurements revealed a 90% contribution to ferromagnetism from the Ti ions and a 10% contribution from the O ions. RBS/channelling measurements show complete Ta substitution in the Ti sites though carrier activation was only 50% at 5% Ta concentration implying compensation by cationic defects. The role of Ti vacancy and Ti3+ was studied via XAS and x-ray photoemission spectroscopy (XPS) respectively. It was found that in films with strong ferromagnetism, the Ti vacancy signal was strong while Ti3+ signal was absent. We propose (in the absence of any obvious exchange mechanisms) that the localised magnetic moments, Ti vacancy sites, are ferromagnetically ordered by itinerant carriers. Cationic-defect-induced magnetism is an alternative route to ferromagnetism in wide-band-gap semiconducting oxides without any magnetic elements.

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A. Rusydi, S. Dhar, A. Roy Barman, Ariando, D. -C. Qi, M. Motapothula, J. B. Yi, I. Santoso, Y. P. Feng, K. Yang, Y. Dai, N. L. Yakovlev, J. Ding, A. T. S. Wee, G. Neuber, M. B. H. Breese, M. Ruebhausen, H. Hilgenkamp, T. Venkatesan. 2012-07-13. Cationic vacancy induced room-temperature ferromagnetism in transparent conducting anatase Ti_{1-x}Ta_xO_2 (x~0.05) thin films. https://doi.org/10.1098/rsta.2012.0198

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