Effect of microwave processing on Mn doped ZnO diluted magnetic semiconductor characteristics

Abstract

5 and 7.5 at% Mn doped ZnO samples were prepared by microwave treatment following thermal curing. The XRD phase analysis reveals the Mn may be present in the unreacted Mn3O4 form or bonded with wurtzite ZnO forming substitutional solid solution (Zn0.99Mn0.01O and Zn0.95Mn0.05O) or spinel (ZnMn2O4). The Fourier transform infra-red (FTIR) band shift to higher wavenumber for the microwave treated samples appearing at 538 and 619 cm−1 indicates formation of ZnMn2O4 spinel structure. Identification of tiny particles in the wall of ZnO lamellae and decrease in Zn2p binding energy signifies vigorous chemical changes taken place on microwave treatment. The structural evolution was depicted by 3d modelling. Quantitative estimation of Mn in the samples was performed by microwave plasma atomic emission spectroscopy (MPAES) and the result matches with the calculated value. Raman spectroscopy shows clear peaks of ZnO, Mn3O4 and MnO2 compounds for all the samples prepared. Whereas, shoulder peak of ZnMn2O4 is observed for 7.5 at% Mn doped microwave pre-treated sample. The optical absorption spectra show major peak near to 360 nm signifying bandgap of ZnO in the visible range. The cation substitution in the host lattice by dopant creates oxygen vacancy (VO) in excess, responsible for increasing bound magnetic polaron, which is clearly evidenced by the presence of broad PL peak near to 535 nm and 548 nm for microwave treated samples. The microwave treatment assists the incorporation of Mn into ZnO lattice as evidenced by reduction of photoluminescence (PL) peak intensity. The magnetic hysteresis loop (B-H curve) of the samples clearly shows increase in saturation magnetisation by ~16.1 and ~24.7 % on microwave treatment of 5 and 7.5 at% Mn doped ZnO respectively.