Ferromagnetism of cobalt-doped anatase TiO2 studied by bulk- and surface-sensitive soft x-ray magnetic circular dichroism

We have studied magnetism in anatase Ti1-xCoxO2-delta (x = 0.05) thin films with various electron carrier densities, by soft x-ray magnetic circular dichroism (XMCD) measurements at the Co L-2,L-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 mode, while it was 0.3-2.4 mu(B)/Co using the bulk-sensitive total fluorescence yield 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. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4729123]