Abstract
We report here microstructural, magnetic and optical properties of high quality epitaxial thin films of diluted magnetic semiconductor Zn1−xMnxO (0.01≤×≤0.25) grown on (0001) sapphire substrate (α-Al2O3) by pulsed laser deposition technique. Seven (01-10) planes of ZnMnO film are found to match with six (-12-10) planes of sapphire substrate through excellent domain matching epitaxy by 30° rotations of ZnMnO unit cell about c-axis with respect to the sapphire unit cell. From high resolution transmission electron micrograph image the misfit dislocations are observed at the interface of sapphire and ZnMnO film growth plane. The insulating Zn0.82 Mn0.18 O epitaxial thin film showed ferromagnetic behavior (hysteretic) with coercive field ∼6.2 mT, and a maximum saturation moment of 0.42 μB/Mn+2 ion at a field of 0.5 T at the lowest attainable temperature (T=10 K). The strong concave behavior of magnetization as a function of the temperature curves in this strongly insulating ferromagnetic diluted magnetic semiconductor film has been best explained through non-mean-field polaron-percolation-theory. The increase of band gap from bulk ZnO with dopant concentration (x), observed from absorbance spectra, has been attributed to the sp-d spin — exchange interaction between the band electrons and localized d electrons of Mn+2 ions of Zn1−xMnxO films in the presence of tetrahedral crystal field interaction.
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