Heesang Kim

Scaling behaviors for resistive memory switching in NiO nanowire devices

We investigated scaling behaviors for NiO nanowire array devices with different nanowire diameters. Plots of the reset current and the third harmonic generation signal as a function of the on-state resistance (R0) show scaling behaviors for all devices, such as NiO film devices. However, the scaling exponents of NiO nanowire devices were different from those of NiO film devices, and hence the fractal dimension estimated from the scaling exponent was smaller for the NiO nanowire devices than for the NiO film devices. This decrease in the fractal dimension was attributed to the confinement of the conducting filaments within each nanowire.

Manipulation of spin states by dipole polarization switching

A ferromagnetic/ferroelectric hybrid double quantum disk structure is proposed, capable of manipulating spin states. Switching of spontaneous electric polarization of the ferroelectric quantum disk changes the potential profile of the system and induces ground state transition. Two carrier spin states are separated into ferroelectric semiconductor and diluted magnetic semiconductor disks via asymmetric Zeeman splitting of the coupled quantum disks. The proof of the spin separation resulting from the dipole polarization switching is shown by the probability density change of the lowest energy subband. Evolution of the spin state is also predicted from the subband energy diagram as a function of the bias voltage.

Magnetoconductance of a hybrid quantum ring: Effects of antidot potentials

The electronic structures and two-terminal magnetoconductance of a hybrid quantum ring are studied. The backscattering due to energy-resonance is considered in the conductance calculation. The hybrid magnetic-electric quantum ring is fabricated by applying an antidot electrostatic potential in the middle of a magnetic quantum dot. Electrons are both magnetically and electrically confined in the plane. The antidot potential repelling electrons from the center of the dot plays a critical role in the energy spectra and magnetoconductance. The angular momentum transition in the energy dispersion and the magnetoconductance behavior are investigated in consideration of the antidot potential variation. Results are shown using a comparison of the results of the conventional magnetic quantum dot.

Multiferroic control of magneto-current through a resonant tunneling diode

We study the resonant tunneling magneto-resistance (TMR) of a multiferroic resonant tunneling diode, which is hybridized of ferroelectric double barriers and a ferromagnetic quantum well. Using the nonequilibrium Green’s function method we show that magneto-currents through the resonant tunneling diode and its current spin polarization can be manipulated by changing the relative direction of an applied magnetic field to the spontaneous magnetic field in the diluted magnetic semiconductor quantum well as well as by reversing dipole polarization directions in ferroelectric barriers. With these results, we propose a multiferroic spin device to control the amount of current and spin polarization of current through it.

Manipulation of spin distribution in double quantum disks with external magnetic field

A ferromagnetic/non-magnetic hybrid-double-quantum-disk (HDQD) structure formed in a nanorod is proposed, which is capable of manipulating the spatial profile of the carrier spins of the system by changing the longitudinal (perpendicular to the disks) external magnetic field. Synergy between size-asymmetrical disks and the difference of g-factors induces energy-level crossing and redistribution of the spin when the external magnetic field changes. The carriers spin polarization profile is shown as well as the probability density change in the energy subband of each carrier. Characteristics of the structure can be applied to spin devices such as memory devices.

Variation of the extended s-wave superconducting order parameter: From s-wave to g-wave

We investigate evolution of properties of an extended

Spin filtering in magnetic barrier structures with in-plane spin orientation

s

CONTROLLABLE SPIN POLARIZATION IN A DMS QUANTUM DOT

-wave superconductor, when the order parameter varies from an

Curie-temperature modulation by electric fields in Mn δ-doped asymmetric double quantum wells

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Magnetization Anisotropy of Semiconductor Quantum Wires with Magnetoelectric Quantization

-wave to a