Preparation and Magnetic Properties of Transition-metal-doped SnO$_2$

There is strong interest in the ferromagnetism (FM) at room temperature in doped oxides, e.g., Co or Fe doped SnO$_{2 }$[1, 2]. We report the preparation and magnetic properties of transition-metal-doped SnO$_{2}$ (Sn$_{1-x}$TM$_{x}$O$_{2}$, TM=V and Mn, x=0--0.05). Bulk and thin-film samples were prepared by solid-state reaction and pulsed-laser deposition, respectively, and characterized by X-ray diffraction, electron microscopy and SQUID magnetometry. The magnetic properties strongly depend on the sample-processing temperature. Room-temperature FM has been observed in the bulk samples sintered at a low temperature of 500 $^{\circ}$C, but not in those sintered or annealed at higher temperatures (650 $^{\circ}$C and 900 $^{\circ}$C for TM=V and Mn, respectively). Additional Sb-doping has no strong effect on the FM, while vacuum annealing enhances the FM. Effects of sample-processing conditions and additional Sb-doping on the magnetic properties will be discussed. This research is supported by ONR, NSF-MRSEC, W. M. Keck Foundation and CMRA. [1]. S. B. Ogale, et al., Phys. Rev. Lett. 91, 077205 (2003). [2]. J. M. D. Coey, et al., Appl. Phys. Lett. 84, 1332 (2004).