arXiv subjects

Soon Cheol Hong

Publications and source records attributed to Soon Cheol Hong.

7 recordsLinked to original sources

arXiv2026

Microscopic Origin of Polarization-Controlled Magnetization Switching in FePt/BaTiO$_3$

Electric-field driven magnetization switching in FePt/BaTiO$_3$ (001) is demonstrated through first-principles calculations. The magnetic easy axis of FePt layer undergoes a transition from in-plane to perpendicular direction upon ferroelectric polarization reversal, a process sensitively controlled by epitaxial strain with threshold strain strain($\eta$) $\eta\approx\%$. At this phenomena, a large interfacial magnetoelectric coupling ($\alpha_I = 3.6 \times 10^{-10}$ G$\cdot$cm$^2$/V) is responsible, stemming from the orbital reconstruction. In particular, the redistribution of Pt-$d$ orbital occupancy alters spin-orbit coupling, thereby tuning the competition between magnetic anisotropy ($K_i$) and magnetoelastic energy ($b_1$). Our work clarifies the fundamental physics of strain-engineered magnetoelectricity and suggests a concrete pathway for designing ultra-low-power voltage-controlled magnetic memory.

cond-mat.mtrl-sci↗

arXiv2021

Spin-Orbit Torque Engineering in β-W/CoFeB Heterostructures via Ta and V Alloying at Interfaces

Spin-orbit torque manifested as an accumulated spin-polarized moment at nonmagnetic normal metal, and ferromagnet interfaces is a promising magnetization switching mechanism for spintronic devices. To fully exploit this in practice, materials with a high spin Hall angle, i.e., a charge-to-spin conversion efficiency, are indispensable. To date, very few approaches have been made to devise new nonmagnetic metal alloys. Moreover, new materials need to be compatible with semiconductor processing. Here we introduce W-Ta and W-V alloys and deploy them at the interface between $β$-W/CoFeB layers. First, spin Hall conductivities of W-Ta and W-V structures with various compositions are carried out by first-principles band calculations, which predict the spin Hall conductivity of the W-V alloy is improved from $-0.82 \times 10^3$ S/cm that of W to $-1.98 \times 10^3$ S/cm. Subsequently, heterostructure fabrication and spin-orbit torque properties are characterized experimentally. By alloying $β$-W with V at a concentration of 20 at%, we observe a large enhancement of the absolute value of spin Hall conductivity of up to $-(2.77 \pm 0.31) \times 10^3$ S/cm. By employing X-ray diffraction and scanning transmission electron microscopy, we further explain the enhancement of spin-orbit torque efficiency is stemmed from W-V alloy between W and CoFeB.

cond-mat.mtrl-sci↗

arXiv2020

Anisotropic Behavior of Excitons in Single Crystal α-SnS

We investigate analytically the anisotropic dielectric properties of single crystal α-SnS near the fundamental absorption edge by considering atomic orbitals. Most striking is the excitonic feature in the armchair- (b-) axis direction, which is particularly prominent at low temperatures. To determine the origin of this anisotropy, we perform first-principles calculations using the GW0 Bethe-Salpeter equation (BSE) including the electron-hole interaction. The results show that the anisotropic dielectric characteristics are a direct result of the natural anisotropy of p orbitals. In particular, this dominant excitonic feature originates from the py orbital at the saddle point in the Γ-Y region.

cond-mat.mtrl-sci↗

arXiv2020

Enhanced voltage-controlled magnetic anisotropy via magneto-elasticity in FePt/MgO(001)

The interplay between magneto-electricity (ME) and magneto-elasticity (MEL) is studied in the context of voltage-controlled magnetic anisotropy (VCMA). Strain plays more than a role of changing lattice constant but that of the internal electric field in the heterostructure. As a prototype, FePt/MgO(001) is visited, where the behavior of two interfaces are drastically different: one exhibits switching the other does not. Whether an external electric field ($E_{ext}$) is present or not, we found VCMA coefficient larger than 1 pJ/V$\cdot$m, as a consequence of the rearrangement of $d$ orbitals with $m=\pm1$ and $\pm2$ in response to an external electric field. In addition, magneto-crystalline anisotropy (MA) is analyzed with strain taken into account, where non-linear feature is presented only accountable by invoking second-order MEL.

cond-mat.mtrl-sci↗

arXiv2016

Density Functional Theory study on the electronic structure and thermoelectric properties of strained Mn4Si7

The strain effect on electronic structure and thermoelectric properties of Higher Manganese Silicides (HMSs) Mn4Si7 was studied using Density Functional Theory (DFT) and through solving Boltzman Transport Equation (BTE). We found that the tensile strain attempts to reduce the band gap while the compressive strain not much affect to band gap. The Seebeck coeficient was found to be increased with increasing temperature, which is very consistent to experiments. The electrical conductivity and power factor show highly degree of anisotropy, where in-plane direction is more dominant. The different behavior of electrical conductivity along in-plane and outof plane direction was explained due to the change of band dispersion in the valence band maximum (VBM).

cond-mat.mtrl-sci↗

arXiv2015

Surface-termination dependent magnetism and strong perpendicular magnetocrystalline anisotropy of a FeRh (001) thin film: A density-functional study

Magnetism of FeRh (001) films strongly depends on film thickness and surface terminations. While magnetic ground state of bulk FeRh is G-type antiferromagnetism, the Rh-terminated films exhibit ferromagnetism with strong perpendicular MCA whose energy +2.1 meV/$\Box$ is two orders of magnitude greater than 3$d$ magnetic metals, where $\Box$ is area of two-dimensional unit cell. While Goodenough-Kanamori-Anderson rule on the superexchange interaction is crucial in determining the magnetic ground phases of FeRh bulk and thin films, the magnetic phases are results of interplay and competition between three mechanisms - the superexchange interaction, the Zener direct-interaction, and magnetic energy gain.

cond-mat.mtrl-sci↗

arXiv2008

Vacancy-induced magnetism in SnO$_{2}$: A density functional study

We study the magnetic and electronic properties of defects in SnO$_{2}$ using pseudopotential and all electron methods. Our calculations show that bulk SnO$_{2}$ is non-magnetic, but it shows magnetism with a magnetic moment around 4.00 $μ_{B}$ due to Sn vacancy (V$_\mathrm{Sn}$). The magnetic moment comes mainly from O atoms surrounding V$_\mathrm{Sn}$ and Sn atoms, which couple antiferromagnetically with the O atoms in the presence of V$_\mathrm{Sn}$. The coupling between different Sn vacancies is also studied and we find that these defects not only couple ferromagnetically but also antiferromagnetically and ferrimagnetically. Our calculations demonstrate that the experimentally observed giant magnetic moment of transition metal doped SnO$_{2}$ can be attributed to V$_\mathrm{Sn}$.

cond-mat.mtrl-sci↗