Indication of intrinsic room-temperature ferromagnetism in Ti 1 − x Co x O 2 − δ thin film: An x-ray magnetic circular dichroism study

Soft x-ray magnetic circular dichroism (XMCD) measurements at the Co L 2 , 3 edges of Co-doped rutile Ti O 2 at room temperature revealed clear multiplet features characteristic of ferromagnetic Co 2 + ions coordinated by O 2 − ions, being in sharp contrast to the featureless XMCD spectrum of Co metal or metallic clusters. The absorption and XMCD spectra agree well with a full atomic-multiplet calculation for the Co 2 + high-spin state in the D 2 h -symmetry crystal field at the Ti site in rutile Ti O 2 . The results indicate that the ferromagnetism arises from the Co 2 + ions substituting the Ti 4 + ions.