Juwon Lee

Towards a new class of heavy ion doped magnetic semiconductors for room temperature applications

The article presents, using Bi doped ZnO, an example of a heavy ion doped oxide semiconductor, highlighting a novel p-symmetry interaction of the electronic states to stabilize ferromagnetism. The study includes both ab initio theory and experiments, which yield clear evidence for above room temperature ferromagnetism. ZnBixO1−x thin films are grown using the pulsed laser deposition technique. The room temperature ferromagnetism finds its origin in the holes introduced by the Bi doping and the p-p coupling between Bi and the host atoms. A sizeable magnetic moment is measured by means of x-ray magnetic circular dichroism at the O K-edge, probing directly the spin polarization of the O(2p) states. This result is in agreement with the theoretical predictions and inductive magnetometry measurements. Ab initio calculations of the electronic and magnetic structure of ZnBixO1−x at various doping levels allow to trace the origin of the ferromagnetic character of this material. It appears, that the spin-orbit energy of the heavy ion Bi stabilizes the ferromagnetic phase. Thus, ZnBixO1−x doped with a heavy non-ferromagnetic element, such as Bi, is a credible example of a candidate material for a new class of compounds for spintronics applications, based on the spin polarization of the p states.

Room temperature ferromagnetic and ambipolar behaviors of MoS2 doped by manganese oxide using an electrochemical method

We report the room temperature ferromagnetic and ambipolar behaviours of MoS2 thin flakes doped with MnO2 by electrochemical adsorption. The MoS2 thin film was determined to be multilayered over four layers from Raman analysis. The Mn-oxide doped MoS2 has a ferromagnetic hysteresis at room temperature and showed a weak remnant magnetization, 0.02 emu/g. From the gate dependent transfer characteristics of the MoS2 field effect transistor, it appeared that the Mn-oxide doped MoS2 has ambipolar behaviours with field effect mobilities of about 3.7 and 16.3 cm2 V−1 s−1, respectively, for electrons and holes.

Formation and magnetic properties of InFeP:Ag nanorods fabricated with noble metal Ag using an ion milling method

The formation including density, and height of InFeP:Ag nano-rods doped with noble metal Ag using ion milling method was preponderantly determined from TEM and XRD analyses. We investigate especially the enhanced ferromagnetism of the well aligned InFeP:Ag nano-rods. AES and XPS measurements were carried out in order to investigate the incorporation of Ag and to verify the local chemical bonding of InFeP:Ag nano-rods. The variation of FWHM for DCRC and TAD peaks demonstrates that noble metal Ag is incorporated into InFeP:Ag nano-rods. The noticeable ferromagnetic signature (M-H curve) of the InFeP:Ag nano-rods is observed and Tc persists up to near 350 K (3.9 × 10-4 emu/g) from temperature - dependence magnetization (M-T curve) measurements. This study suggests that the InFeP:Ag nano-rods should be a potential candidate for the application of spintronic devices.

Room temperature transparent conducting magnetic oxide (TCMO) properties in heavy ion doped oxide semiconductor

Bismuth doped ZnO (ZnBi0.03O0.97) thin films are grown using pulsed laser deposition. The existence of positively charged Bi, absence of metallic zinc and the Zn-O bond formation in Bi doped ZnO are confirmed using X-ray Photoelectron Spectroscopy (XPS). Temperature dependent resistivity and UV-visible absorption spectra show lowest resistivity with 8.44 × 10-4 Ω cm at 300 K and average transmittance of 93 % in the visible region respectively. The robust ferromagnetic signature is observed at 350 K (7.156 × 10-4 emu/g). This study suggests that Bi doped ZnO films should be a potential candidate for spin based optoelectronic applications.