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Spin Hall conductivity of Tungsten alloys
Sonny H. Rhim,Quynh Anh T. Nguyen,Do Duc Cuong,Soon Cheol Hong 한국자기학회 2021 한국자기학회 학술연구발표회 논문개요집 Vol.31 No.2
In this talk, spin Hall conductivities of three Tungsten alloys, W-V alloy, W-Nitrides, and W-Silicide, are presented with comparison of their values and underlying Berry curvatures. First-principles calculations are performed using VASP package along with Wannierization, where Kubo formula is used to evaluate Berry curvature and spin Hall conductivities. In all cases, anti-crossing regions guaranteed by symmetry, crossing due to symmorphic and nonsymmorphic little group, are responsible for large Berry curvature: each stemming from bcc structure and rock-salt structure. Regarding W-Si, we show preliminary result of 6.25 % Si concentration comparing other higher concentrations with less stability. Further, unexplored task in spin Hall conductivity using DFT calculations is revealed.
Symmetry Effects on Magnetocrystalline Anisotropy of hcp and fcc Cobalt: a First-principles Study
Thi H. Ho,Sonny H. Rhim,S. C. Hong 한국자기학회 2021 한국자기학회 학술연구발표회 논문개요집 Vol.31 No.1
Density-functional theory calculations are performed to investigate symmetry effects on magnetocrystalline anisotropy (MCA) of Co. Both bulk and films in the hcp and fcc phases are considered. Within the framework of second-order perturbation theory<sup>[1]</sup>, MCA energy can be decomposed into spin channels, i.e., the spin-conserved ↑↑ and ↓↓, and the spin-flip ↑↓ and ↓↑ terms. Here, the first spin (↑ or ↓) symbol represents an occupied state, while the second spin (↑ or ↓) one does an unoccupied state. For example, ↑↓ represents the coupling between an occupied ↑ state and an unoccupied ↓ state. The spin-channel decomposed MCAs of hcp and fcc Co in bulk are presented in Fig. 1. Generally, each spin channel contribution behaves in a quite similar way for both hcp and fcc Co. However, the net MCAs are quite different, 15.61 µeV/atom of hcp Co and 0.53 µeV/atom of fcc Co, whose reason should be revealed. In both hcp and fcc Co, the majority spin(↑) bands are almost completely filled so that the negligible unoccupied ↑ states cannot play a dominant role in determining a MCA energy. As a result, the spin channels of ↑↑ and ↓↑ contribute much smaller than those of ↓↓ and ↑↓, as shown in Fig. 1. The big difference between the MCAs of hcp and fcc Co comes mostly from the positive spin-flip ↑↓ and the negative spin-conserved ↓↓ terms. The negative spin-conserved ↓↓ term of hcp Co is much smaller by 13.17 µeV/atom in absolute value than that of fcc Co, while the positive spin-flip ↑↓ term of hcp Co has higher MCA by 2.0 µeV/atom than that of fcc Co, which results in the much stronger MCA of hcp Co than fcc Co. In thin films, the surface effects are found to enhance MCA energies of both hcp and fcc Co. For the 9-ML films, the MCA energies of 253.04 and 207.64 µeV are obtained for hcp and fcc Co, respectively. Interestingly, the MCA energy of the fcc Co film is in the same order of magnitude as that of the hcp Co film. The reason is due to the dominant MCA contribution of the surface layers. The MCA values of surface layers are 171.8 and 188.7 µeV/atom for the hcp and fcc Co, respectively.
임성현(Sonny H. Rhim) 한국자기학회 2023 韓國磁氣學會誌 Vol.33 No.6
This review aims a brief and short-handed overview on altermagnetism, a new magnetic phase recently proposed. The altermagnetism is mostly regarded as d-wave magnetism, as a counterpart of d-wave superconductivity. Hence, short-handed summary on d-wave superconductivity in terms of gap symmetry is provided. As symmetry arguments are unavoidable in discussing altermagnetism, operators consisting of groups, more specifically spage group and spin group, are introduced. As final remark, the comparison between antiferromagentism and altermagnetism is outlined.
TiO<sub>2</sub>/RbPbI<sub>3</sub> halide perovskite solar cells
Jung, Mi-Hee,Rhim, Sonny H.,Moon, Dohyun North-Holland 2017 Solar Energy Materials and Solar Cells Vol. No.
<P><B>Abstract</B></P> <P>Inorganic-organic halide perovskites hold the great promise for next-generation photovoltaics due to their excellent high performance and low cost. However, major limitation for the commercialization of perovskite solar cell can be attributed to the transformation and degradation of lead halide perovskite during the exposure of environmental humidity and photon irradiation. To solve these problems, herein, we apply the one-dimensional and inorganic RbPbI<SUB>3</SUB> perovskite into the solar cell because it shows the superior stability in environmental conditions. After RbPbI<SUB>3</SUB> perovskite was applied into the solar cell with a FTO/TiO<SUB>2</SUB>/RbPbI<SUB>3</SUB>/Spiro-MeOTAD/Au configuration, the device exhibits an open circuit voltage of 0.62V, photocurrent density of 3.75mA/cm<SUP>2</SUP>, fill factor of 44.60%, and 1.04% of PCE by reverse sweeping direction. Even though the performance of RbPbI<SUB>3</SUB> device was still lower than other perovskite solar cells, this approach enabled us to establish the key step to make a highly stable perovskite film, leading to the best photovoltaic performance for real applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We applied the RbPbI<SUB>3</SUB> to a solar cell to determine the performance of 1D perovskite. </LI> <LI> RbPbI<SUB>3</SUB> perovskite shows the superior stability for the environmental conditions. </LI> <LI> The band gap alignment of RbPbI<SUB>3</SUB> perovskite is well matched with that of TiO<SUB>2</SUB>. </LI> <LI> The device with RbPbI<SUB>3</SUB> perovskite shows little hysteresis in the <I>J</I>-V scan direction. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>The solar cell was fabricated with one dimensional RbPbI<SUB>3</SUB> perovskite as a light absorber.</P> <P>[DISPLAY OMISSION]</P>