Determination of charge state in Co- and Mn-doped ZnO films

We have investigated Co- and Mn-alloyed ZnO films grown by pulsed laser deposition (PLD) on a-plane sapphire substrates. X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) measurements have been performed at beamline 8.0.1 and beamline 6.3.1 at the Advanced Light Source in Berkeley, USA. From XAS spectra, recorded in both total electron yield and total fluorescence yield mode, the valence states of Mn and Co have been determined. No ferromagnetic properties have been observed by means of XMCD at 20 K at the L2,3-absorption edges of Mn and Co, respectively. This observation agrees with the purely paramagnetic response of those Co- and Mn-alloyed ZnO films from SQUID magnetometry and Hall effect measurements.