Sang Jun Cha | Searcharxiv

arXiv2020

Spin Transport in the heterogeneous structure containing Topological Insulator and Diluted Magnetic Semiconductor

In this paper, we discuss spin transport in topological insulator (TI) and diluted magnetic semiconductor (DMS) heterogeneous structures. In DMS / FM (Ferromagnetic Metal) heterogeneous structure, the spin injection efficiency changes according to the electric field and Fermi energy were investigated. The higher electric field, the stronger spin injection efficiency, and its velocity of increase gets lower and approaches to the equilibrium state. Additionally, the higher interface conductivity, the weaker spin injection efficiency, and the transmission due to Fermi energy of spin up and spin down is different from each other. In the same structure, the spin injection efficiency changes depending on the magnetic field, and the spin injection efficiency vibrates sensitively according to the magnetic field. In TI / DMS heterogeneous structure, the spin current changes according to magnetic field were investigated. Here, when the magnetic field is low, the spin current oscillates, and as the magnetic field increases, the vibration is attenuated. It also decreases with increasing temperature and weakens vibrations. This is due to the competitive effect of the chiral properties of Dirac type quasiparticles in the topological insulator and the unique properties of exchange interaction between electrons and ions in DMS. This result allows us to expect the possibility of spintronic devices with high sensitivity to magnetic field.

cond-mat.mes-hall↗

arXiv2020

Recrystallization Characteristics of Catalytic Alloy and Graphite in Diamond Synthesis

We first consider the recrystallization characteristics of catalysis alloy and graphite in the process of diamond synthesis under the condition of super high pressure and high temperature in catalysis method. In the process of diamond synthesis catalysis metal is plastically deformed by increase of pressure and then recrystallized as increasing the temperature. As catalysis metal is recrystallized, the shape of graphite particle is in spherical shape in the region contacting with the catalyst but in any shape in the opposite region. In addition, we calculate the electron charge density distribution and cohesive energies of cementite structure using the first principle method to investigate the reciprocal interaction between transient metal elements and carbon atoms in high-temperature catalyst synthesis. After determination of lattice constant parameters, we obtain the cohesive energy by subtracting the total energy of the crystal from the summation of total energies of atoms composing the crystal and dividing it by the number of atoms. Therefore, the effect of the catalyst on the diamond synthesis is to be analyzed theoretically.

cond-mat.mtrl-sci↗