Haeng-Ki Lee

Magnetic Properties of Cr-doped LiNbO₃ by Using the Projection Operator Technique

The electron spin resonance lineshape (ESRLS) function for the electron spin resonance linewidth (ESRLW) of Cr³? (S = 3/2) in ferroelectric lithium niobate single crystals doped with 0.05 wt% of Cr, is obtained by using the projection operator technique (POT), developed by Argyres and Sigel. The ESRLS function is calculated to be axially symmetric about the c ? axis and analyzed by using the spin Hamiltonian H SP = μB (BㆍgㆍS) + SㆍDㆍS with the parameters g = 1.972 and D = 0.395 ㎝?¹. In the ca plane, the linewidths show a strong angular dependence, whereas in the ab plane, they are independent of the angle. This result implies that the resonance center has an axial symmetry along the c ? axis. Further, from the temperature dependence of the linewidths that is shown, it can be seen that the linewidths increase as the temperature increases, at a frequency of v = 9.27㎓. This result implies that the scattering effect increases with increasing temperature. Thus, the POT is considered to be more convenient to explain the scattering mechanism as in the case of other optical resonant systems.

Different behaviors of half-metallic ferromagnetism of Cr-doped AlN and InN

The electronic structure and magnetism are studied for the zinc-blende and wurtzite (Al,Cr)N, (Ga,Cr)N and (In,Cr)N by using the full potential linear muffin-tin orbital method. The energy gap (quasi-gap) in Cr-doped wurtzite InN decreases exponentially with increasing the Cr concentration from 0.027 to 0.166. The half-metallicity is retained in the whole range of concentrations considered, whereas for (Al,Cr)N, the half-metallic character disappears at a concentration of 0.166. The Cr magnetic moment in AlN is about 2.12–2.40μB Cr atom−1 with changing the Cr concentration, and for Cr in InN, it is a nearly constant value of 3.0 μB Cr atom−1.

Electronic Structure and Magnetic Moments of Copper-atom in/on GaN Semiconductor

The electronic and magnetic properties of Cu-doped GaN with a Cu concentration of 6.25% and 12.5% are examined theoretically using the full-potential linear muffin-tin orbital method. The magnetic moment of Cu atoms decreases with increasing Cu concentration. The spin-polarization of Cu atoms is reduced due to the Cu d-d interaction depending on the distance between the nearest neighbouring Cu atoms. Cu atoms exhibits a clustering tendency in GaN. For Cu-adsorbed GaN thin films with a surface coverage of 0.25, the ferromagnetic state is found to be the energetically favourable state with an induced magnetic moment of 0.54 μ B per supercell.

Effects of Nitrogen Defect on Magnetism of Cu-doped InN

We investigate the electronic and magnetic properties in Cu-doped InN with the N vacancy (VN) from first principles calculations. There is the long-range ferromagnetic order between two Cu atoms, attributed to the hole-mediated double exchange through the strong p-d interaction between the Cu atom and neighboring N atom. The system of VN defect in Cu-doped InN has the lowest formation energy. Due to the hybridization between the Cu-3d and VN states, the spin-polarization on the Cu atoms in the InN lattice is reduced by VN defect. So, it shows a weak ferromagnetic behavior.

Investigation of the Hyperfine Structure Effect in a Mn-Doped LiNbO 3

The computer program (EPR-NMR program version 6.2) employed here sets up the spin Hamiltonian matrices and determines their eigenvalues using exact diagonalization. We study the electron spin resonance for in ferroelectric single crystals. The self-energy is obtained using the projection operator method developed by Argyres and Sigel. The self-energy is calculated to be axially symmetric about the by the spin Hamiltonian. The line-widths decreased as the temperature increased; we assume that the hyperfine structure transition is a more dominant scattering than the other transitions. We conclude that the calculation process presented in this study is useful for quantum optical transitions.

Half-Metallic Ferromagnetism in Chalcopyrite (AlGaMn)P2 Alloys

We studied the electronic and magnetic properties of (Al1−yMny)GaP2 (Ga-rich) and Al(Ga1−yMny)P2 (Al-rich) with y = 0.03125, 0.0625, 0.09375, and 0.125 by using the first-principles calculations. The ferromagnetic Mn-doped AlGaP2 chalcopyrite is the most energetically favorable one. The spin polarized Al(GaMn)P2 state (Al-rich system) is more stable than spin polarized (AlMn)GaP2 state (Ga-rich) with the magnetic moment of 3.8 /Mn. The Mn-doped AlGaP2 yields strong half-metallic ground states. The states of host Al, Ga, or P atoms at the Fermi level are mainly a P-3p character, which mediates a strong interaction between the Mn-3d and P-3p states.

Line-profile Formula in the Carbon Nanotubes by Electron Spin Resonance

Abstract : The line-width of carbon nanotubes (CNTs) was studied as a function of the temperature at a frequency of 9.49 GHz in the presence of external electromagnetic radiation. The relative frequency dependence of the absorption power is obtained with the projection operator technique (POT) proposed by Kawabata. The line-width increased as the temperature increased in the high-temperature region (T>200 K). The scattering is little affected in the low-temperature region (T<200 K) because there is no correlation between the resonance field and the Fermi-Dirac distribution function. Thus, the present technique is considered to be more convenient to explain the resonant system as in the case of other optical transition problems. Keywords: ESR, CNTs, Projection operator, Line-profile, Line-widths, INTRODUCTION Electron spin resonance (ESR) spectroscopy has been used to assess the quality of carbon nanotube, CNT. 1 In ESR experiments, one applies a static magnetic field and measures the absorption power of electromagnetic radiation polarized perpendicular to the field direction. In the absence of SU(2) spin symmetry breaking terms in the system Hamiltonian, the absorption power is then simply

Investigation of Temperature Dependence for CNT Semiconductor in External Magnetic Field

We calculated the electron spin resonance (ESR) line-profile function. The line-width of single-walled carbon nanotube (SWNT) was studied as a function of the temperature at a frequency of 9.5 GHz in the presence of external electromagnetic radiation. The temperature dependence of the line-widths is obtained with the projection operator method (POM) proposed by Argyres and Sigel. The scattering is little affected in the low-temperature region (T