Epitaxial growth and magnetic and electric properties of Co-doped TiO2 thin films
Is nonequilibrium doping an essential for ferromagnetism?
Institute of Physics, Chinese Academy of Sciences,
Beijing 100080, PR China
2 Centre for Superconducting and Magnetic Materials and Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542
3 Temasek Laboratories, Engineering Drive 3, 10 Kent Ridge Crescent, Singapore 119260
Corresponding author: a email@example.com
Revised: 7 March 2003
Published online: 7 May 2003
In this research, c-axis oriented epitaxial anatase TiO2 thin films were grown on substrates using a ceramic target by Pulsed Laser Deposition (PLD). The film growth processes were monitored by reflective high energy electronic diffraction (RHEED). Microstructure, conductivity, and magnetism of these doped films are found strongly affected by the oxygen pressure and substrate temperature Ts. Grown at a Ts around 750 °C in an oxygen pressure of 0.2 mbar, the dopants are found existing as oxide inclusions. The doped film thus behaves as an insulator and shows diamagnetism in a magnetic field parallel to the film surface. However, in the doped film grown at a reduced temperature of 630 °C in a vacuum, no impurity phase can be identified. The film shows a saturated magnetic moment of 0.16 µB/Co and a fairly good conductivity at room temperature. It is then concluded that nonequilibrium growth at lower temperatures in vacuum is essential for a high solubility of Co in the TiO2 lattice and thus the ferromagnetism.
PACS: 75.50.Pp – Magnetic semiconductors / 81.15.Fg – Laser deposition / 68.55.Jk – Structure and morphology; thickness; crystalline orientation and texture / 61.14.Hg – Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2003