${\text{Zn}}_{1-x}{\text{Co}}_x\text{O}$ epitaxial films codoped with Al were studied using a combination of synchrotron-based x-ray absorption spectroscopies and classical magnetometry. Phase purity was verified by comparing the x-ray linear dichroism with simulations and previously published reference spectra. The existence of weak ferromagnetism or inhomogeneous superparamagnetism is evidenced at low temperatures by classical magnetometry. A combination of x-ray absorption spectroscopies indicates that its origin is most likely of extrinsic character such as magnetic impurities or the onset of phase separation rather than weak, electron mediated ferromagnetism.

• Received 18 May 2010

DOI:https://doi.org/10.1103/PhysRevB.82.041202