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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 −2 full width at half maximum values of 78 arc sec for the undoped ZnO and 252 arc sec for Zn 1−x Mn x O ͑x = 0.05͒. The lattice parameter of the Zn 1−x Mn x O was observed to increase with Mn concentration. Transmission measurements showed systematic variations dominated by absorption from interatomic Mn 2+ and Co 2+ 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 Zn 1−x Mn x O dominated by an antiferromagnetic Mn-Mn exchange interaction at low temperatures. Zn 1−x Co x O 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 Zn 1−x TM x O is not ferromagnetic; thus creative processing and doping techniques are necessary to achieve practical ferromagnetism in these materials.

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