Magnetic properties of bulk Zn1-xMnxO and Zn1-xCoxO single crystals -: art. no. 023906

Manganese and cobalt-doped ZnO have been produced using a modified melt-growth technique. X-ray diffraction measurements indicate that the samples are high-quality single crystals with omega-2theta full width at half maximum values of 78 arc sec for the undoped ZnO and 252 arc sec for Zn1-xMnxO (x=0.05). The lattice parameter of the Zn1-xMnxO was observed to increase with Mn concentration. Transmission measurements showed systematic variations dominated by absorption from interatomic Mn2+ and Co2+ transitions. No evidence of diluted magnetic semiconductor mean-field ferromagnetic behavior was observed in any of these nominally noncarrier-doped samples. The magnetic properties instead showed paramagnetic behavior for Zn1-xMnxO dominated by an antiferromagnetic Mn-Mn exchange interaction at low temperatures. Zn1-xCoxO showed hysteresis that was attributed to superparamagnetic Co clusters embedded in a diamagnetic ZnO matrix. It has been shown that in the bulk single-crystal form, intrinsic and noncarrier-doped Zn1-xTMxO is not ferromagnetic; thus creative processing and doping techniques are necessary to achieve practical ferromagnetism in these materials. (C) 2005 American Institute of Physics.