Ferromagnetism of cobalt-doped anatase TiO$_2$ studied by bulk- and   surface-sensitive soft x-ray magnetic circular dichroism
  We have studied magnetism in anatase Ti$_{1-x}$Co$_x$O$_{2-\delta}$ ({\it x} = 0.05) thin films with various electron carrier densities, by soft x-ray magnetic circular dichroism (XMCD) measurements at the Co $L_{2,3}$ absorption edges. For electrically conducting samples, the magnetic moment estimated by XMCD was $<$ 0.3 $\mu_B$/Co using the surface-sensitive total electron yield (TEY) mode, while it was 0.3-2.4 $\mu_B$/Co using the bulk-sensitive total fluorescence yield (TFY) mode. The latter value is in the same range as the saturation magnetization 0.6-2.1 $\mu_B$/Co deduced by SQUID measurement. The magnetization and the XMCD intensity increased with carrier density, consistent with the carrier-induced origin of the ferromagnetism. 
V. R. Singh, K. Ishigami, V. K. Verma, G. Shibata, Y. Yamazaki, T.   Kataoka, A. Fujimori, F.-H. Chang, D.-J. Huang, H.-J. L...
cond-mat.str-el