Jeongdae Seo

Magnetic force microscopy of conducting nanodots in NiO thin films

We report a nanoscale magnetic conducting filament in a resistive random access memory (RRAM) device by the direct investigation of conducting nanobits in NiO thin films using magnetic force microscopy. The conducting nanobit in a NiO RRAM capacitor formed by CAFM and KFM exhibited a typical bistable resistive switching characteristic. The magnetizations of the conducting nanobit were measured as a function of the set-reset switching cycle and as the switching cycles were increased, a strong ferromagnetic signal was observed. The metallic Ni formation in the nanoscale magnetic conducting filament could be a possible reason for the origin of the magnetism.

Mn doping effect on the ferroelectric domain structure of BaTiO3 thin films

We comparatively investigated the ferroelectric domain structure of BaTiO3 (BTO) and Mn-doped BTO epitaxial thin films grown on Pt/MgO substrates by pulsed laser deposition. The advantages of Mn doping included enhanced ferroelectric polarization, low leakage current, and ferromagnetism. Piezoresponse force microscopy revealed that the increased domain wall energy associated with Mn doping led to an increase in the ferroelectric domain structure.

Enhanced Multiferroic Properties in Epitaxial Yb-Doped BiFeO3 Thin Films

AbstractWe report the enhanced multiferroic properties of a ytterbium (Yb)- doped BiFeO3 thin film (Bi0.85Yb0.15FeO3) deposited on a (001) SrRuO3/(100) SrTiO3 substrate by pulsed laser deposition. The crystal structure, surface morphology, ferroelectric domain structure, and the electrical and magnetic behavior of the epitaxial Bi0.85Yb0.15FeO3 film, 100 nm in thickness, were investigated. The results were compared with those of an undoped BiFeO3 thin film. The x-ray diffraction patterns showed that both films have tetragonal-like crystal structures. Atomic force microscopy showed that the Bi0.85Yb0.15FeO3 and BiFeO3 films have flat and clear surface steps, characteristic of a layer-by-layer growth mechanism. Furthermore, the strip-like ferroelectric domain structures were clearly observed in piezoelectric force microscopy. The Bi0.85Yb0.15FeO3 films had significantly higher remanent polarizations of approximately 73 μC/cm2 and lower leakage currents compared to the BiFeO3 thin film. Ferromagnetic enhancement was also observed in the Bi0.85Yb0.15FeO3 film at room temperature.

Multiferroic YCrO3 thin films grown on glass substrate: Resistive switching characteristics

Polycrystalline YCrO3 thin films were deposited on (111) Pt/Ta/glass substrates by pulsed laser deposition. The YCrO3 thin films exhibited good ferroelectric properties with remnant polarization of about 5 µC/cm2. Large leakage current was observed by I-V curve and ferroelectric hysteresis loop. The YCrO3 resistive random access memory (RRAM) capacitor showed unipolar switching behaviors with SET and RESET voltages higher than those of general NiO RRAM capacitors.