Hyeongwoo Seo

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.

Magnetic frustration, realized in the special geometrical arrangement of localized spins, often promotes topologically nontrivial spin textures in the real space and induces significantly large unconventional Hall responses. This spin Berry curvature effect in itinerant frustrated magnets mainly works with a static spin order, limiting the effective temperature range below the magnetic transition temperature and yielding the typical anomalous Hall conductivity below ~ 10³ Ω⁻¹cm⁻¹. Here we show that an ultraclean triangular-lattice antiferromagnet PdCrO₂ exhibits a large anomalous Hall conductivity up to ~ 10⁶ Ω⁻¹cm⁻¹ in the paramagnetic state, which is maintained far above the Neel temperature (T_N) up to ~ 4T_N. The reported enhancement of anomalous Hall response above T_N is attributed to the skew scattering of highly mobile Pd electrons to fluctuating but locally-correlated Cr spins with a finite spin chirality. Our findings point at an alternative route to realizing high-temperature giant anomalous Hall responses, exploiting magnetic frustration in the ultraclean regime.

Iridates have attracted much interest in the last decade for their novel magnetism emerging in the limit of strong spin-orbit coupling and possible unconventional superconductivity. A standard for growing iridate single crystals has been the flux method using platinum crucibles. Here, we show that this widely used method compromises the sample quality by inclusion of platinum impurities. We find that Sr2IrO4 single crystals grown in iridium crucibles show remarkable differences from those grown in platinum crucibles in their sample characterizations using Raman spectroscopy, resistivity, magnetization, optical third harmonic generation, resonant X-ray diffraction, and resonant inelastic X-ray scattering measurements. In particular, we show that several peaks of sizable intensities disappear in the Raman spectra of samples free of platinum impurities, and a significantly larger activation energy is extracted from the resistivity data compared to previously reported values. Furthermore, we find no evidence of the previously reported glide symmetry breaking structural distortions and confirm the I41/acd space group of the lattice symmetry. Although the platinum impurities are not apparent in the magnetic properties and thus went unnoticed in the stoichiometric insulating phase for a long time, their effects can be much more detrimental to transport properties in chemically doped compounds. Therefore, our result suggests using growth methods that avoid platinum impurities for an investigation of intrinsic physical properties of iridates, and possible superconducting phases.