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.

Epitaxial layers of Ga 1−x Mn x N with concentrations of up to x = 0.015 have been grown on c-sapphire substrates by metalorganic chemical vapour deposition. No ferromagnetic second phases were detected via high-resolution x-ray diffraction. Crystalline quality and surface structure were measured by x-ray diffraction and atomic force microscopy, respectively. No significant deterioration in crystal quality and no increase in surface roughness with the incorporation of Mn were detected. Optical measurements show a broad emission band attributed to a Mn-related transition at 3.0 eV that is not seen in the underlying GaN virtual substrate layers. Room temperature ferromagnetic hysteresis has been observed in these samples, which may be due to either Mn-clustering on the atomic scale or the Ga 1−x Mn x N bulk alloy.

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The lattice vibrations of undoped hexagonal Ga1−xMnxN (x from 0.0% to 1.5%) epitaxial films grown on c-plane sapphire substrates by metalorganic chemical vapor deposition have been investigated using infrared reflectance spectra in the frequency region of 200–2000cm−1 (5–50μm) at room temperature. The experimental reflectance spectra were analyzed using the Lorentz oscillator model for infrared-active phonon observed. The E1(LO) phonon frequency slightly decreases with increasing Mn composition. However, the E1(TO) phonon frequency linearly increases with the Mn composition, which can be well expressed by (558.7+350x)cm−1 and the broadening values are found to be larger than that of the GaN film. It indicates that Mn incorporation decreases the peak values (from the E1 phonon) of the infrared dielectric functions due to the local variation in the lattice constants and to the destruction of the crystal translational symmetry.

The ferromagnetic semiconductor GaMnN has been produced by two methods – ion implantation and metalorganic chemical vapor deposition (MOCVD). P‐type, n‐type, and intrinsic GaN layers grown by MOCVD were ion‐implanted with 3 × 1016/cm2 Mn+ at 200 keV and subsequently annealed under various conditions. Considerable lattice damage is observed by analyzing the peak asymmetry in X‐ray diffraction; annealing only partially recovers this damage. Second phases (MnxNy, GaxMny and Mn4–xGaxN1–y) have been detected upon subsequent annealing. Epitaxial GaMnN layers have been fabricated by MOCVD using Cp2Mn as the manganese precursor. These films were specular and exhibited an increasing dark reddish‐brown tinge with increasing Mn‐concentration and thickness, consistent with GaMnN grown by other methods. X‐ray diffraction revealed symmetric peaks with almost identical lattice parameters to undoped GaN, and no macroscopic second phase formation. Magnetic hysteresis is observed in the ion implanted as well as in MOCVD‐grown films at room temperature. Stronger magnetization was present in the implanted p‐type films and unannealed MOCVD‐grown films, providing evidence that Fermi level control is important for the magnetic properties of these materials. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)