arXiv subjects

Yuqing Ge

Publications and source records attributed to Yuqing Ge.

10 recordsLinked to original sources

arXiv2025

Characterization of Nuclear and Magnetic Structures of Wolframite-Type MgReO4 and ZnReO4

We utilized high-pressure methods to synthesize the oxides AReO$4$ (A=Zn, Mg) and characterized their crystal structures as monoclinic wolframite-type. By combining muon spin spectroscopy ($\mu^+$SR) with DFT calculations for muon stopping sites, we identify two possible magnetic spin structures for both compounds: $\Gamma_3$ with the propagation vector $\mathbf{k} = (0,1/2,0)$ and $\Gamma_4$ with $\mathbf{k} = (0,0,0)$. In both cases, the magnetic moments are canted from the principal axes within the $ac$-plane. The ordered moment of the proposed structures is $\mathbf{0.29(5)~\mu\mathrm{B}}$ for $\Gamma_3$ and $\mathbf{0.25(8)~\mu_\mathrm{B}}$ for $\Gamma_4$. The low moment is consistent with the absence of a magnetic contribution to the neutron powder diffraction (NPD) spectra. Bond valence sum (BVS) analysis supports the oxidation state of Re being Re$^{6+}$ in the compounds, and we suggest that a combination of $t_\mathrm{2g}$ orbital splitting due to spin-orbit coupling (SOC) and $d$-$p$ orbital hybridization is responsible for the strongly suppressed ordered magnetic moment.

cond-mat.mtrl-sci↗

arXiv2025

Persistent Uncorrelated Magnetic Domains in Fe/Si Multilayers and their suppression by incorporating 11B4C

This study investigates magnetic domains in Fe/Si and Fe/Si + B4C multilayers using spin flip off-specular polarized neutron reflectometry. The results show that Fe/Si multilayers exhibit pronounced spin flip off-specular scattering originating from magnetic domains that are uncorrelated out of plane. With increasing external magnetic field the domains progressively coalesce and their magnetization rotates toward alignment with the applied field, approaching a homogeneous magnetic state at higher fields. In contrast, Fe/Si + B4C multilayers exhibit no detectable spin flip off-specular scattering already at low fields, indicating that the multilayer reaches magnetic saturation at significantly lower applied fields. The scattering patterns are interpreted using distorted wave Born approximation simulations in BornAgain, enabled by our added code for simulating magnetic domains and magnetic ordering. To further probe the magnetic behavior, low-energy mu+SR measurements were performed, representing the first mu+SR investigation of polarizing neutron optics multilayers. Together with comparison to previously reported VSM data, these measurements provide insight into the magnetic behavior across short range, medium range, and long range length scales. The results show that incorporating approximately 15 vol.% B4C makes the magnetic configuration highly responsive to external magnetic fields, with clear sensitivity to both in-plane and out-of-plane field geometries. These results show that B4C suppresses magnetic domains and spin flip off-specular scattering, improving Fe/Si coatings for neutron polarization optics in regards to off-specular scattering, and other applications requiring easy magnetic manipulation.

cond-mat.mtrl-sci↗

arXiv2024

Differentially Private Spatiotemporal Trajectory Synthesis with Retained Data Utility

Spatiotemporal trajectories collected from GPS-enabled devices are of vital importance to many applications, such as urban planning and traffic analysis. Due to the privacy leakage concerns, many privacy-preserving trajectory publishing methods have been proposed. However, most of them could not strike a good balance between privacy protection and good data utility. In this paper, we propose DP-STTS, a differentially private spatiotemporal trajectory synthesizer with high data utility, which employs a model composed of a start spatiotemporal cube distribution and a 1-order Markov process. Specially, DP-STTS firstly discretizes the raw spatiotemporal trajectories into neighboring cubes, such that the model size is limited and the model's tolerance for noise could be enhanced. Then, a Markov process is utilized for the next location point picking. After adding noise under differential privacy (DP) to the model, synthetic trajectories that preserve essential spatial and temporal characteristics of the real trajectories are generated from the noisy model. Experiments on one real-life dataset demonstrate that DP-STTS provides good data utility. Our code is available at https://github.com/Etherious72/DP-STTS.

cs.CR↗

arXiv2022

Confirming the high pressure phase diagram of the Shastry-Sutherland model

A Muon Spin Rotation ($\mu$+SR) study was conducted to investigate the magnetic properties of SrCu2(BO3)2 (SCBO) as a function of temperature/pressure. Measurements in zero field and transverse field confirm the absence of long range magnetic order at high pressures and low temperatures. These measurements suggest changes in the Cu spin fluctuations characteristics above 21 kbar, consistent with the formation of a plaquette phase as previously suggested by inelastic neutron scattering measurements. SCBO is the only known realisation of the Shatry-Sutherland model, thus the ground state mediating the dimer and antiferromagnetic phase is likekly to be a plaquette state.

cond-mat.str-el↗

arXiv2022

Magnetic Properties of Multifunctional $^7$LiFePO$_4$ under Hydrostatic Pressure

LiFePO$_4$ (LFPO) is an archetypical and well-known cathode material for rechargeable Li-ion batteries. However, its quasi-one-dimensional (Q1D) structure along with the Fe ions, LFPO also displays interesting low-temperature magnetic properties. Our team has previously utilized the muon spin rotation ($\mu^+$SR) technique to investigate both magnetic spin order as well as Li-ion diffusion in LFPO. In this initial study we extend our investigation and make use of high-pressure $\mu^+$SR to investigate effects on the low-$T$ magnetic order. Contrary to theoretical predictions we find that the magnetic ordering temperature as well as the ordered magnetic moment increase at high pressure (compressive strain).

cond-mat.str-el↗

arXiv2022

Refined magnetic structure of VI$_3$

The van der Waals ferromagnet (FM), VI$_3$, was studied by muon spin relaxation ($\mu^+$SR) and first principle calculations based on density functional theory (DFT). Temperature dependent zero field muon spin relaxation ($\mu^+$SR) measurements confirm the onset of long range FM order and the time spectra exhibits clear muon spin precession frequencies for $T<T_{\rm C}=50.03(1)$~K. The calculated internal magnetic fields at the predicted muon sites, based on the established magnetic structure from neutron diffraction, is inconsistent with the measured one. This inconsistency is because of strong incoherent neutron scattering and absorption originating from the elements V and I. Instead, a new and a more accurate magnetic structure is derived based on a combined study using $\mu^+$SR and DFT. These results suggest strong contritions from orbital angular momentum, providing experimental evidence for the existence of unquenched orbital angular momentum of V$^{3+}$ in VI$_3$. Finally, an unusual form of a short range ordering is present above $T_{\rm C}$. Its temperature dependence is unlike previously reported cases in other layered compounds and its microscopic origin is discussed.

cond-mat.str-el↗

arXiv2022

Magnetic nature of wolframite MgReO$_4$

Rhenium oxides belonging to the family $A$ReO$_4$ where $A$ is a metal cation, exhibit interesting electronic and magnetic properties. In this study we have utilized the muon spin rotation/relaxation ($\mu^+$SR) technique to study the magnetic properties of the MgReO$_4$ compound. To the best of our knowledge, this is the first investigation reported on this interesting material, that is stabilized in a wolframite crystal structure using a special high-pressure synthesis technique. Bulk magnetic studies show the onset of an antiferromagnetic (AF) long range order, or a possible singlet spin state at $T_{\rm C1}\approx90$~K, with a subtle second high-temperature transition at $T_{\rm C2}\approx280$~K. Both transitions are also confirmed by heat capacity ($C_p$) measurements. From our $\mu^+$SR measurements, it is clear that the sample enters an AF order below $T_{\rm C1}=T_{\rm N}\approx85$~K. We find no evidence of magnetic signal above $T_{\rm N}$, which indicates that $T_{\rm C2}$ is likely linked to a structural transition. Further, via sensitive zero field (ZF) $\mu^+$SR measurements we find evidence of a spin reorientation at $T_{\rm Cant}\approx65$~K. This points towards a transition from a collinear AF into a canted AF order at low temperature, which is proposed to be driven by competing magnetic interactions.

cond-mat.str-el↗

arXiv2022

Enhanced thermally-activated skyrmion diffusion with tunable effective gyrotropic force

Magnetic skyrmions, topologically-stabilized spin textures that emerge in magnetic systems, have garnered considerable interest due to a variety of electromagnetic responses that are governed by the topology. The topology that creates a microscopic gyrotropic force also causes detrimental effects, such as the skyrmion Hall effect, which is a well-studied phenomenon highlighting the influence of topology on the deterministic dynamics and drift motion. Furthermore, the gyrotropic force is anticipated to have a substantial impact on stochastic diffusive motion; however, the predicted repercussions have yet to be demonstrated, even qualitatively. Here we demonstrate enhanced thermally-activated diffusive motion of skyrmions in a specifically designed synthetic antiferromagnet. Suppressing the effective gyrotropic force by tuning the angular momentum compensation leads to a more than 10 times enhanced diffusion coefficient compared to that of ferromagnetic skyrmions. Consequently, our findings not only demonstrate the gyro-force dependence of the diffusion coefficient but also enable ultimately energy-efficient unconventional stochastic computing.

cond-mat.mtrl-sci↗

arXiv2021

Constructing coarse-grained skyrmion potentials from experimental data with Iterative Boltzmann Inversion

In an effort to understand skyrmion behavior on a coarse-grained level, skyrmions are often described as 2D quasi particles evolving according to the Thiele equation. Interaction potentials are the key missing parameters for predictive modeling of experiments. We apply the Iterative Boltzmann Inversion technique commonly used in soft matter simulations to construct potentials for skyrmion-skyrmion and skyrmion-magnetic material boundary interactions from a single experimental measurement without any prior assumptions of the potential form. We find that the two interactions are purely repulsive and can be described by an exponential function for experimentally relevant skyrmions. This captures the physics on experimental time and length scales that are of interest for most skyrmion applications and typically inaccessible to atomistic or micromagnetic simulations.

cond-mat.mtrl-sci↗

arXiv2020

Commensurability between element symmetry and the number of skyrmions governing skyrmion diffusion in confined geometries

Magnetic skyrmions are topological magnetic structures, which exhibit quasi-particle properties and can show enhanced stability against perturbation from thermal noise. Recently, thermal Brownian diffusion of these quasi-particles has been found in continuous films and applications in unconventional computing have received significant attention, which however require structured elements. Thus, as the next necessary step, we here study skyrmion diffusion in confined geometries and find it to be qualitatively different: The diffusion is governed by the interplay between the total number of skyrmions and the structure geometry. In particular, we ascertain the effect of circular and triangular geometrical confinement and find that for triangular geometries the behavior is drastically different for the cases when the number of skyrmions in the element is either commensurate or incommensurate with a symmetric filling of the element. This influence of commensurability is corroborated by simulations of a quasi-particle model.

cond-mat.mtrl-sci↗