Cationic-vacancy-induced room-temperature ferromagnetism in transparent, conducting anatase Ti 1− x Ta x O 2 ( x ∼0.05) thin films Academic Article uri icon

abstract

  • We report room-temperature ferromagnetism (FM) in highly conducting, transparent anatase Ti(1-x)Ta(x)O(2) (x∼0.05) thin films grown by pulsed laser deposition on LaAlO(3) 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 Ti(3+) 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 Ti(3+) 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.

authors

  • Rusydi, A
  • Dhar, S
  • Barman, A Roy
  • Ariando
  • Qi, D-C
  • Motapothula, M
  • Yi, JB
  • Santoso, I
  • Feng, YP
  • Yang, K
  • Dai, Y
  • Yakovlev, NL
  • Ding, J
  • Wee, ATS
  • Neuber, G
  • Breese, MBH
  • Ruebhausen, M
  • Hilgenkamp, H
  • Venkatesan, T

publication date

  • October 28, 2012