Young-Dong Ko

Epitaxial stabilization of artificial hexagonal GdMnO3 thin films and their magnetic properties

The authors investigated the role of oxygen partial pressure on the epitaxial growth of an artificial hexagonal GdMnO3 phase, which should exist in an orthorhombic structure in bulk. The hexagonal GdMnO3 film showed diverse, but obvious, magnetic phase transitions with highly enhanced ferromagnetic properties. Its remnant magnetization at 4.2K is higher than those of other hexagonal RMnO3 (R=Ho, Er, and Yb) compounds, and the Curie temperature increases by around 25K. The results demonstrate that the epitaxial stabilization technique is a promising method for fabricating an artificial material with enhanced magnetic properties.The authors investigated the role of oxygen partial pressure on the epitaxial growth of an artificial hexagonal GdMnO3 phase, which should exist in an orthorhombic structure in bulk. The hexagonal GdMnO3 film showed diverse, but obvious, magnetic phase transitions with highly enhanced ferromagnetic properties. Its remnant magnetization at 4.2K is higher than those of other hexagonal RMnO3 (R=Ho, Er, and Yb) compounds, and the Curie temperature increases by around 25K. The results demonstrate that the epitaxial stabilization technique is a promising method for fabricating an artificial material with enhanced magnetic properties.

Local strain-induced 90° domain switching in a barium titanate single crystal

Local strain analysis for a BaTiO3 single crystal under electric loads was conducted using x-ray microdiffraction technique. During the polarization reversal, local 90° domain switchings were observed at certain positions instead of uniform 180° domain switching. Field-dependent strain analysis demonstrated that inhomogeneous domain switching was strongly related to local strain distributions. The results can be understood in terms of competition between elastic and electrostatic energies and provide a crystallographic evidence for the role of local strains on 90° domain switching.

Effects of Saccharine N-Propane Sulfonate on the Microstructures, Magnetic Properties, and Magnetoimpedance of Electroplated Ni – Fe Permalloy Thin Films

We have studied the effects of an organic additive, saccharine N-propane sulfonate, on the microstructures, magnetic properties, and magnetoimpedance of electroplated Ni-Fe Permalloy thin films. Compared to thin films prepared with a pure inorganic electrolyte, the Ni-Fe Permalloy thin films electroplated with electrolytes containing the additive have different crystalline orientation, grain size, surface roughness, coercivity, permeability, and magnetoimpedance. There is a strong correlation between the observed structural changes and the changes in the magnetic properties, such as in the coercivity and permeability. The changes are also dependent on the structure of the electroplating cells. By using an appropriate plating cell, the coercivity can be reduced from 0.36 to 0.08 Oe. These changes in the magnetic properties result in an increase in the magnetoimpedance by 31%.

Properties Change of Electroplated Permalloy Thin Films by Organic Additives

We investigated the changes of the magnetic properties in electroplated Permalloy thin films by a few organic additives added to the plating electrolytes. Under identical electroplating conditions, the crystalline orientations and the surface roughness of the plated thin films were different from those prepared with a pure electrolyte. These property changes reduced the coercivity and increased the magnetoimpedance ratio (MIR) up to 20%.

Generation of large-scale flows due to the small-scale drift-wave turbulence

Summary form only given, as follows. Numerical simulation is performed of the two-dimensional plasma with to a view studying the generation of large-scale flows through the short-scale drift-wave turbulence. The electrostatic turbulence is modeled by Hasegawa-Mima equation with or without an external forcing. Both the shift of the frequency and the nonlinear growth rate of the long-wavelength drift wave will be investigated and the comparison will be made with the proposed predator-prey dynamical system. Without the waves, the energy cascades from the smaller scales to the larger ones and accumulates at the largest possible scale. However, the energy cascade is impeded by the presence of the waves whose frequencies are of the same order as the effective vorticity. As a result, under certain conditions, large-scale zonal flows may develop in the neutral fluids. In addition, plasmas have another important scale in the ion gyro-radius, which may keep the energy cascade from reaching the largest scale and help developing the coherent vortices In this poster, detailed analyses will be presented. regarding the formation of the large-scale flows in terms of the various parameters such as the external forcing, the ion gyro-radius, the dissipation and the system size.