| AVS 59th Annual International Symposium and Exhibition | |
| Oxide Heterostructures-Interface Form & Function Focus Topic | Monday Sessions |
| Session OX+EM+MI+NS+TF-MoM |
| Session: | Structure–Property Relationships in Epitaxial Oxide Interfaces |
| Presenter: | M. Hordagoda, University of South Florida |
| Authors: | D. Mukherjee, University of South Florida M. Hordagoda, University of South Florida R.H. Hyde, University of South Florida N. Bingham, University of South Florida H. Srikanth, University of South Florida P. Mukherjee, University of South Florida S. Witanachchi, University of South Florida |
| Correspondent: | Click to Email |
The low solubility of Mn (equilibrium limit of 13 %) and precipitation of Mn oxides at slightly higher Mn doping (> 4 %) have remained major obstacles in the growth of Mn doped ZnO (ZnO:Mn) thin films for potential spintronic applications. In this work, epitaxial ZnO:Mn thin films were deposited on c-cut Al2O3 (0001) substrates, with increasing Mn concentrations from 2 to 12 %, using the dual-laser ablation process. In this process, an excimer (KrF) laser and a CO2 laser pulses are spatially and temporally overlapped onto the target surface. Initially the target is heated by the CO2 laser to produce a transient molten layer, from which the slightly time-delayed KrF laser initiates the ablation. Ablation for a momentary liquid target not only results in a drastic reduction of particulates in the deposited films but also overcomes the problem of non-congruent ablation of the ZnO:Mn target, leading to stoichiometric film deposition. Moreover, the optimum coupling of the laser energies produces an ablation plume that has a broader angular distribution, compared to the plume generated by KrF pulse alone, as observed from the intensified-charge-coupled-detector (ICCD) images of the ablated plumes. This allows the deposition of uniform films over larger area. Further, the higher ionization of the ablated species as seen in the optical emission spectra (OES) of the dual-laser ablated plumes leads to enhanced gas phase reaction and better film morphology and crystallinity. X-ray diffraction studies revealed that the dual-laser deposited ZnO:Mn films were single crystalline with no secondary phase formation even at 12 % doping while single-laser deposited ZnO:Mn films showed secondary Mn oxide phases. Room temperature magnetic measurements showed ferromagnetism (FM) with enhanced saturation magnetization (Ms) values from 1.3 emu/cm3 for 2 % ZnO:Mn films to 2.9 emu/cm3 for 12 % ZnO:Mn films. In- and out-of-plane magnetization revealed absence of magnetic anisotropy. Further, temperature dependent Hall measurements showed a strong correlation between the effective carrier densities and the observed FM. All these measurements suggested a carrier mediated mechanism of FM in ZnO:Mn thin films. Using both the experimental data and theoretical analysis the FM in less conducting ZnO:Mn films was described by a bound magnetic polaron model whereas that in highly conducting films was consistent with a carrier mediated interaction via RKKY exchange mechanism.