Structural and magnetic properties of Zn1 − xMnxO nanocrystalline powders and thin films

Abstract

The structural and magnetic properties of Zn1−xMnxO (x=0, 0.02, 0.05, 0.1) nanocrystalline powders and thin epitaxial films were studied in detail. Epitaxial films were fabricated by pulsed laser deposition on c-Al2O3 substrates. To this end, ablation targets were prepared by pressing nano-sized powders of Zn1−xMnxO (x=0, 0.02, 0.1) synthesized by the wet polymeric precursor method. The method was chosen in order to improve purity and homogeneity of the grain-size distribution. The epitaxial growth was optimized with respect to crystalline quality by varying deposition parameters such as substrate temperature, laser fluence and background gas conditions. Films prepared under optimized conditions show a mosaic spread<0.3° and a bulk-like c-axis lattice parameter of 5.198Å. The structural data indicate the substitution of Zn2+ by the Mn2+ cations in the wurtzite structure of pristine ZnO. The influence of Mn on the lattice dynamics of ZnO is confirmed by Raman scattering. It is found that Mn doping increases the lattice defects and induces two Raman vibration modes of 275 and 526cm−1. Magnetic measurements, in turn, show while thin films, grown in vacuum, are ferromagnetic at RT, the growth in an oxygen atmosphere results in a dramatic decrease of the magnetic properties, demonstrating that oxygen vacancies are most likely responsible for the magnetic exchange. The co-doping with nitrogen has no major influence on the structural and magnetic properties of the ZnO films. A correct Mn doping concentration seems to be crucial for making a viable diluted magnetic semiconductor.