Joonyoung Choi

Has attracted considerable attention, yet the origin of its intriguing magnetic behaviors remains elusive due to limited insight into its low‐energy anisotropy. Here, high‐field torque magnetometry measurements are performed, revealing a previously unrecognized anisotropic spin response that reflects interaction terms beyond the standard XY or XXZ models. In combination with relativistic density functional theory calculations and magnetic force response theory, an effective low‐energy spin Hamiltonian is constructed, elucidating not only the observed anomalous magnetic behavior but also other recent experiments. Remarkably, the magnetic dipole interaction and the associated spin‐flop transition play a crucial role in driving the deviation from two‐dimensional spin alignment, providing direct insight into the underlying anisotropic energy hierarchy. The generalized Hamiltonian can serve as the important fundamental ground for future study, and our approach adopted here will hopefully be relevant to many other related material systems.

Kagome‐lattice magnets provide a fertile ground for exploring exotic electronic phases due to topological band structures and complex magnetic orders. Yet, how these ingredients dictate unconventional magnetotransport responses, crucial for possible spintronic applications, has remained elusive. Here, we show that a prototypical kagome antiferromagnet exhibits significant magnetic‐field‐driven redistribution of Berry curvature and the colossal anomalous Hall conductivity (AHC). Under high magnetic fields, spin canting induces a pronounced spin splitting of the flat and Dirac bands near the Fermi level, dramatically enhancing the Berry curvature. The resulting AHC reaches 2.5 10 S/cm, far exceeding the intrinsic Berry curvature predictions and ranking among the highest reported in magnetic systems. This colossal AHC enhancement is attributed to a synergy between field‐tuned Berry curvature and enhanced skew scattering in the clean limit. Our findings highlight the critical role of magnetic‐field‐controlled spin splitting in engineering Berry curvature and anomalous magnetotransport in clean kagome magnets.

Interface-engineered hybrid nanocomposites offer considerable potential for spintronic applications, yet their spin-dependent transport mechanisms remain poorly understood. Here, we report the solvothermal synthesis of Fe3O4/reduced graphene oxide (RGO) nanocomposites, in which ∼25 nm Fe3O4 nanoparticles are uniformly dispersed on conductive RGO sheets. The nanocomposites exhibit a 250-fold decrease in room-temperature resistance, and their low-temperature charge transport is dominated by disorder-driven, non-ideal hopping conduction associated with interfacial coupling and percolative transport pathways, as revealed by Zabrodskii analysis. Magnetotransport measurements (2–300 K, up to 9 T) show a crossover from negative to positive magnetoresistance, reaching +2.0% at 2 K, which is five times larger than that of pristine Fe3O4. The magnetoresistance behavior is interpreted in terms of competing spin-dependent scattering and field-enhanced localization in the disordered Fe3O4/RGO network. These findings demonstrate that Fe3O4/RGO nanocomposites provide a versatile platform for controlling spin-dependent transport through interfacial and disorder engineering.

Electrical control of quantum magnetic states is essential in spintronic science. Initial studies on the ferromagnetic state control were extended to collinear antiferromagnets and, more recently, noncollinear antiferromagnets. However, electrical control mechanisms of such exotic magnetic states remain poorly understood. Here, we report the first experimental and theoretical example of the current control of helical antiferromagnets, arising from the competition between collinear antiferromagnetic exchange and interlayer Dzyaloshinskii-Moriya interaction in new van der Waals (vdW) material Ni_{1/3}NbS_{2}. Due to the intrinsic broken inversion symmetry, an in-plane current generates spin-orbit torque that, in turn, interacts directly with the helical antiferromagnetic order. Our theoretical analyses indicate that a weak ferromagnetic order coexists due to the Dzyaloshinskii-Moriya interaction, mediating the spin-orbit torque to collectively rotate the helical antiferromagnetic order. Our Ni_{1/3}NbS_{2} nanodevice experiments produce current-dependent resistance change consistent with the theoretical prediction. This Letter widens our understanding of the electrical control of helical antiferromagnets and promotes vdW quantum magnets as interesting material platforms for electrical control.

The anomalous Hall conductivity (AHC) in magnetic materials, resulting from inverted band topology, has emerged as a key adjustable function in spin‐torque devices and advanced magnetic sensors. Among systems with near‐half‐metallicity and broken time‐reversal symmetry, cobalt disulfide (CoS ₂ ) has proven to be a material capable of significantly enhancing its AHC. In this study, the AHC of CoS ₂ is empirically assessed by manipulating the chemical potential through Fe‐ (hole) and Ni‐ (electron) doping. The primary mechanism underlying the colossal AHC is identified through the application of density functional theory and tight‐binding analyses. The main source of this substantial AHC is traced to four spin‐polarized massive Dirac dispersions in the k _z = 0 plane of the Brillouin zone, located slightly below the Fermi level. In Co _0.95 Fe _0.05 S ₂ , the AHC, which is directly proportional to the momentum‐space integral of the Berry curvature (BC), reached a record‐breaking value of 2507 Ω ⁻¹ cm ⁻¹ . This is because the BCs of the four Dirac dispersions all exhibit the same sign, a consequence of the d ‐wave‐like spin‐orbit coupling among spin‐polarized e _g orbitals.