양찬호 교수

BiFeO(3) is one of the most studied multiferroic materials. Both its magnetic and ferroelectric properties can be influenced by doping. A large body of work on the doped material has been presented in the past couple of years. In this paper we provide a perspective on general doping concepts and their impact on the material's functionality.

Abstract Transition metal oxides (TMOs) are an important class of materials that show a wide range of functionalities involving spin, charge, and lattice degrees of freedom. The strong correlation between electrons in d -orbitals and the multivalence nature give rise to a variety of exotic electronic states ranging from insulator to superconductor and cause intriguing phase competition phenomena. Despite a burst of research on the multifarious functionalities in TMOs, little attention has been p

Abstract Topological defects in matter behave collectively to form highly non-trivial structures called topological textures that are characterised by conserved quantities such as the winding number. Here we show that an epitaxial ferroelectric square nanoplate of bismuth ferrite subjected to a large strain gradient (as much as 10 5 m −1 ) associated with misfit strain relaxation enables five discrete levels for the ferroelectric topological invariant of the entire system because of its peculiar

Bi ions of multiferroic $\mathrm{Bi}\mathrm{Mn}{\mathrm{O}}_{3}$ were replaced with La ions in order to induce an overlap of the ferroelectric and ferromagnetic transitions in temperature and thus enhance the interproperty coupling. Twenty percent La-doped $\mathrm{Bi}\mathrm{Mn}{\mathrm{O}}_{3}$ in thin-film form shows a broad ferroelectric transition below $150\phantom{\rule{0.3em}{0ex}}\mathrm{K}$; spontaneous magnetization also develops in the transition region. The saturation magnetization

This study examines the atomic force microscope (AFM) tip-based electrical formation of tens of microns long stripe (and ∼100 nm wide) inorganic one-dimensional nanostructures based on the morphotropic phase boundary of La-doped BiFeO3 epitaxial thin films. The substitution of Lanthanum into bismuth ferrite not only produces the formation of straight stripe mixed-phase patterns but also improves the spatial continuity drastically by two orders of magnitude. We create, switch and erase stripe nan

Abstract Topological defects have received much attention due to their stability against perturbations and potential applications in nonvolatile high-density memory. Topologically non-trivial textures can be compelled by constraints on boundary condition, geometrical structure, and curved space. Ferroelectric vortices have been realized in various finite-sized nanostructures that allow such constraints to be produced. However, manipulation of topological excitations in otherwise topologically tr

Epitaxial thin films of multiferroic perovskite BiMnO3 were synthesized on SrTiO3 substrates, and orbital ordering and magnetic properties of the thin films were investigated. The ordering of the Mn3+ e(g) orbitals at a wave vector (1/4 1/4 1/4) was detected by Mn K-edge resonant X-rayscattering. This peculiar orbital order inherently contains magnetic frustration. While bulk BiMnO3 is known to exhibit simple ferromagnetism, the frustration enhanced by in-plane compressive strains in the films b

Abstract The emergence of a domain wall property that is forbidden by symmetry in bulk can offer unforeseen opportunities for nanoscale low-dimensional functionalities in ferroic materials. Here, we report that the piezoelectric response is greatly enhanced in the ferroelastic domain walls of centrosymmetric tungsten trioxide thin films due to a large strain gradient of 10 6 m −1 , which exists over a rather wide width (~20 nm) of the wall. The interrelationship between the strain gradient, elec

Resonant x-ray scattering is performed near the Mn $K$-absorption edge for an epitaxial thin film of ${\mathrm{BiMnO}}_{3}$. The azimuthal angle dependence of the resonant (003) peak (in monoclinic indices) is measured with different photon polarizations; for the $\ensuremath{\sigma}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{'}}$ channel a threefold symmetric oscillation is observed in the intensity variation, while the $\ensuremath{\sigma}\ensuremath{\rightarrow}{\ensuremath{\sigma

The ultrafast motion of oxygen vacancies in solids is crucial for various future applications, such as oxide electrolytes. Visualization and quantification can offer unforeseen opportunities to probe the collective dynamics of defects in crystalline solids, but little research has been conducted on oxygen vacancy electromigration using these approaches. Here, we visualize electric-field-induced creation and propagation of oxygen-vacancy-rich and -poor competing phases and their interface with op