Ferromagnetism of cobalt-doped anatase TiO${}_2$ studied by bulk- and surface-sensitive soft x-ray magnetic circular dichroism

Abstract

We have studied magnetism in anatase Ti${}_{1-x}$Co${}_x$O${}_{2-\hat{I}´}$ ({\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 $\hat{I}{¼}_B$/Co using the surface-sensitive total electron yield (TEY) mode, while it was 0.3-2.4 $\hat{I}{¼}_B$/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 $\hat{I}{¼}_B$/Co deduced by SQUID measurement. The magnetization and the XMCD intensity increased with carrier density, consistent with the carrier-induced origin of the ferromagnetism.

Accepted in Applied Physics Letters 2012