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

TL;DR

This study investigates the ferromagnetism in cobalt-doped anatase TiO2 thin films using soft x-ray magnetic circular dichroism, revealing a carrier-induced magnetic behavior with different surface and bulk magnetic moments.

Contribution

It provides the first detailed comparison of surface and bulk magnetic moments in Co-doped TiO2 using XMCD, highlighting the carrier-induced nature of ferromagnetism.

Findings

Bulk magnetic moments range from 0.3 to 2.4 μ_B/Co.

Magnetization increases with carrier density.

Surface and bulk magnetic moments differ significantly.

Abstract

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.