Gyungchoon Go's research while affiliated with Korea Advanced Institute of Science and Technology and other places

... Specifically, effective model approximations, such as the continuum model [6,11,12] and the free-layer-substrate model [7,[13][14][15][16][17][18], exhibit substantial limitations in accuracy. Alternative atomistic spin simulations may offer improved accuracy, but they are hindered by their resource-intensive nature [8][9][10][19][20][21]. Consequently, it is crucial to develop theoretical frameworks that are both efficient and reliable to overcome these constraints and propel advancements in this field. ...

... Although the chirality of magnon is fixed in ferromagnets, symmetry allows two degenerate magnon modes carrying opposite spins in collinear antiferromagnets with easy-axis anisotropy [12][13][14][15][16][17]. With no net magnetization, vanished static stray field, and terahertz response rate, antiferromagnets exhibit unique advantages for robust and ultrafast spin-based nanoscale applications, among which the spin Seebeck effect (SSE) and spin Nernst effect (SNE) are, respectively, effective approaches to longitudinally and transversely transport spins with respect to the temperature gradient [13,15,[17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35]. In collinear antiferromagnet, the SSE often requires a magnetic field to break the spin degeneracy or enhance the spin splitting [12,13,26,36], and more stringently, the SNE exploits the Berry curvature that needs the Dzyaloshinskii-Moriya interaction (DMI) [15,27,37,38] or magnetoelastic coupling [33,34], i.e., the transverse spin current is normally proportional to the spin-orbit coupling (SOC) strength. ...

... This generation of a spin Hall current with unconventional spin directions, even in high-symmetry crystals, is a unique feature of magnetic systems. This phenomenon has also been referred to by various terminologies such as the spin Hall effect with spin rotation 31 , anomalous spin Hall effect 21 , spin-orbit precession 32,33 , and the spin swapping effect 34,35 . ...

... The easy-axis anisotropy breaks the spin O(3) symmetry down to U(1) and the domain wall spontaneously breaks this U(1) symmetry. In a two-dimensional system, a domain wall is a onedimensional object and spin textures can spatially vary along the domain wall when chirality is injected [66]. The chirality injection is tunable by the spin Hall effect of a metal contact at the boundary of the domain wall. ...

... Recent studies have highlighted the potentially crucial role of orbital currents in the dynamics of angular momentum in solids 12,13 . In particular, experimental and theoretical studies suggest that there is an orbital counterpart to spin torqueorbital torque [14][15][16][17][18][19][20][21][22][23] . Orbital torque emerges when an orbital current is injected into an FM layer. ...

... ulate established electronic and photonic components, such as magnonic quantum point contacts, magnonic crystals, magnonic quantum bits, magnonic frequency combs, among others. [25][26][27][28][29][30][31][32][33] Building upon similar ideas, recent theoretical results suggest all-on-chip structures to produce magnonic cavities by magneto-dipole interaction with a chiral magnonic element, [34] using an array of antiferromagnets on a ferromagnet, [35] or by proximity with superconductors. [36] One approach to confining magnons involves the fabrication of rectangular or circular nanoand micro-structures using YIG. ...

... The spin-to-charge conversion facilitated by spin-orbit interaction, has emerged as a key focus in spintronics research due to its potential practical applications for energy-efficient and fast control of magnetization in spintronic devices [1][2][3]. Conventionally, a heavy metal with strong spin-orbit coupling (SOC) is used for this purpose [4][5][6]. The interconversion of electrical charge currents and spin currents in ferromagnet/nonmagnet (FM/NM) multilayers connects electric fields to magnetic torques during the forward process, known as SOT [7][8][9][10]. ...

... where γ is the gyromagnetic ratio, α the Gilbert damping constant, the reduced Planck constant, J c the charge current density injected into the HM, e the electron charge, µ 0 the permeability of vacuum, M s the saturation magnetization, t F the thickness of the free layer, ξ DL and ξ FL are the efficiency constants damping-like torque and field-like torque, m the magnetization unit vector of the free layer, σ is the spin polarization vector. The origin of the damping-like SOT is the spin Hall effect, and the origin of the field-like spin torque is commonly considered a combination of the interfacial Rashba-Edelstein effect and the oersted field from the charge current 34 . We note that by the definition in Eq. (1), the efficiency constant of damping-like SOT, ξ DL , and the efficiency constant of field-like SOT, ξ FL , should have opposite sign to trigger the precessional switching dynamics. ...

... The MR in the yz-plane is more complicated: beside the SMR effect discussed previously, the geometry size effect (GSE) [38][39][40] in the FM layer also contribute to the MR effect in the yz-plane. However, the GSE-induced MR has the character of R z , R y for the NiFe film, 41 which is different from the situation of R y , R z in this work. Therefore, we believe that the GSE is not the origin of the observed MR in the yz-plane, and it should be ascribed to the SMR effect. ...

... The energy difference between the radial and tangential orbitals characterizes the strength of the orbital texture and is parameterized by η in Eq. (1). However, there is no comprehensive understanding of the microscopic origin of the orbital texture because the microscopic origin of η is studied in only for limited cases [7,[15][16][17] and most studies rely on the symmetry argument on the existence of the r-t orbital texture [12,13]. Therefore, a comprehensive microscopic study of orbital textures is desired. ...