Structure and Magnetic Properties of Sn$_{1 - {\rm x}}$ Co$_{\rm x}$ O$_{2}$ Powder and Film

We have studied room-temperature ferromagnetism (RTFM) in Sn
<sub>1

-

x</sub>
Co
_x
O
₂
powders and films fabricated by the sol-gel method. Our X-ray diffraction, high-resolution transmission microscopy, and X-ray photoelectron spectroscopy results show that all the samples have a pure rutile structure, and Co ions have a chemical valence of 2+. In addition, the magnetic moment per Co ion drops rapidly with the increase of Co content. Interestingly, Sn
<sub>1

-

x</sub>
Co
_x
O
₂
films spin-coated on a Si (111) substrate have much larger magnetic moment than powder samples, because film samples have larger domain volumes, which may induce stronger long-range magnetic exchange coupling.