arXiv subjects

Chao-Hung Du

Publications and source records attributed to Chao-Hung Du.

7 recordsLinked to original sources

arXiv2026

Electrothermal control of spin-reorientation transition in Co/Fe_3GaTe_2 heterostructures

Electrical control of magnetic anisotropy in van der Waals (vdWs) magnets is a key step toward reconfigurable two-dimensional spintronics, yet how a conventional metallic ferromagnet competes with a van der Waals magnet across a direct interface has remained largely unexplored. Here we demonstrate reversible thermal and electrothermal control of a spin-reorientation transition in Co/Fe_3GaTe_2 (FGaT) heterostructures. As Joule heating weakens the FGaT anisotropy, the heterostructure switches from an out-of-plane- to an in-plane-dominated state at a reorientation temperature of approximately 311 K, well below the Curie temperature, consistent with an exchange-mediated anisotropy competition between the Co overlayer and FGaT. An electrically driven device shows a closely matching loop evolution within an 80-100 mW power window, reversibly over five measurement cycles, consistent with an electrothermal origin. In a Co-free FGaT device, Kerr microscopy traces the switching to a power-tunable domain nucleation barrier and demonstrates power-thresholded, field-assisted magnetization reversal at a threshold near 15 mW. These results demonstrate electrothermal anisotropy competition as a route to heat-assisted and device-level control of vdWs magnetism.

cond-mat.mes-hall↗

arXiv2026

Magnetic structure in the two-dimensional van der Waals ferromagnet Fe$_3$GaTe$_2$

High-quality single crystals of the two-dimensional van der Waals ferromagnet Fe$_3$GaTe$_2$ (FGaT) were successfully grown using the chemical vapour transport method, which effectively reduced surface impurities compared with conventional self-flux growth. Structural and magnetic characterizations were performed using single-crystal X-ray and neutron diffraction. The results confirm that FGaT crystallizes in the hexagonal $P6_3/mmc$ structure, with Fe occupying two inequivalent sites (Fe$^{i}$ and Fe$^{ii}$), where the magnetic moment of Fe$^{i}$ [1.9(2) $μ_B$] is larger than that of Fe$^{ii}$ [1.4(6) $μ_B$]. The magnetic easy axis is oriented along the $c$ axis and the Curie temperature ($T_C$) is approximately 355-360 K. Compared with Fe$_3$GeTe$_2$ (FGT), FGaT exhibits a slightly expanded $a$ axis and a contracted $c$ axis, resulting in a reduction in the Fe$^{i}$-Fe$^{ii}$ interatomic distance along the $c$ axis. This pronounced contraction could strengthen the Fe$-$Fe exchange interaction, which is believed to be the key factor responsible for the significantly higher $T_C$ in FGaT relative to FGT.

cond-mat.str-el↗

arXiv2025

A double-spiral spin ordering in the helimagnet YBaCuFeO$_{5}$

Materials with a spiral spin ordering always show a rich phase diagram and can be a playground for studying the exotic physical properties associated with spiral magnetism. Using neutron elastic and resonant x-ray scattering on a high-quality single crystal YBaCuFeO$_{5}$, we demonstrate YBaCuFeO$_{5}$ to be a helimagnet consisting of a double-spiral spin ordering. YBaCuFeO$_{5}$ undergoes a commensurate to incommensurate magnetic phase transition at $T_{N2}$$\sim$ 175 K, and the incommensurate phase consists of two spin-ordered components. Both components have different periodicities but with the same propagating direction along the {\it c}-axis below $T_{N2}$. Using resonant x-ray scattering at the Fe and Cu \textit{K}-edges, we further demonstrate that both spiral spin orderings result from the Fe$^{3+}$ and Cu$^{2+}$, respectively, forming a double-spiral spin ordering structure. This can be understood to be caused by the coupling between both sublattices of Fe$^{3+}$ and Cu$^{2+}$ with the atomic lattice.

cond-mat.str-el↗

arXiv2024

Giant X-ray circular dichroism in a time-reversal invariant altermagnet

X-ray circular dichroism, arising from the contrast in X-ray absorption between opposite photon helicities, serves as a spectroscopic tool to measure the magnetization of ferromagnetic materials and identify the handedness of chiral crystals. Antiferromagnets with crystallographic chirality typically lack X-ray magnetic circular dichroism because of time-reversal symmetry, yet exhibit weak X-ray natural circular dichroism. Here, we report the observation of giant natural circular dichroism in the Ni $L_3$-edge X-ray absorption of Ni$_3$TeO$_6$, a polar and chiral antiferromagnet with effective time-reversal symmetry. To unravel this intriguing phenomenon, we propose a phenomenological model that classifies the movement of photons in a chiral crystal within the same symmetry class as that of a magnetic field. The coupling of X-ray polarization with the induced magnetization yields giant X-ray natural circular dichroism, revealing the altermagnetism of Ni$_3$TeO$_6$. Our findings provide evidence for the interplay between magnetism and crystal chirality in natural optical activity. Additionally, we establish the first example of a new class of magnetic materials exhibiting circular dichroism with time-reversal symmetry.

cond-mat.str-el↗

arXiv2018

Excitonic dispersion of the intermediate-spin state in LaCoO$_3$ revealed by resonant inelastic X-ray scattering

More than 50 years ago the electron-hole attraction was proposed to drive narrow gap semiconductors or semimetals to a new phase, the excitonic insulator. The experimental proof of its existence in bulk materials remains elusive. In strongly correlated insulators, the proximity of the excitonic insulator phase is reflected by the presence of dispersive electron-hole excitations with a small gap above a singlet ground state. Recently, such an excitation spectrum was proposed to be realized in perovskite oxide LaCoO$_3$. In this Letter we use Co $L_3$-edge resonant inelastic X-ray scattering to put this proposal to experimental test.

cond-mat.str-el↗

arXiv2014

Inverse Melting of an Electronic Liquid Crystal

Inverse melting refers to the rare thermodynamic phenomenon in which a solid melts into a liquid upon cooling, a transition that can occur only when the ordered (solid) phase has more entropy than the disordered (liquid) phase, and that has so far only been observed in a handful of systems. Here we report the first experimental observation for the inverse melting of an electronic liquid crystalline order in strontium-doped lanthanum nickelate, a compound isostructural with the superconducting cuprates, with a hole doping concentration of 1/3. Using x-ray scattering, we demonstrate that the isotropic charge modulation is driven to nematic order by fluctuating spins and shows an inverse melting transition. Using a phenomenological Landau theory, we show that this inverse melting transition is due to the interlayer coupling between the charge and spin orders. This discovery points to the importance of the interlayer correlations in the system, and provides a new perspective to study the intricate nature of the electronic liquid crystal phases in strongly correlated electronic systems, including possibly the Cu- and Fe-based high-Tc superconductors.

cond-mat.str-el↗

arXiv2004

Direct Measurement of Spatial Distortions of Charge Density Waves in K0.3MoO3

Using X-ray scattering and the technique of multiple diffreactions, we revisit the dynamical transition of charge density waves (CDWs) in K0.3MoO3 under applied voltages. In addition to the usual transport and half width (of Bragg peaks) measurements, we also measure the triplet phase by three-wave diffraction, which provides, for the first time, the {\em direct} evidence for the spatial distortions of CDWs. This novel and sensitive technique developed here can be applied to general periodic media, including stripes in high temperature superconductors, and provide a new perspective into interesting phenomena in these materials.

cond-mat.mtrl-sci↗