arXiv subjects

Madalynn Marshall

Publications and source records attributed to Madalynn Marshall.

12 recordsLinked to original sources

arXiv2026

Pressure-Induced Chemical Bonding Effects on Lattice and Magnetic Instabilities in Antiferromagnetic Insulating CaMn$_2$Sb$_2$

Exotic quantum phenomena often emerge near an electronic delocalization transition (EDT) from an antiferromagnetic insulating phase to a strongly correlated metallic state under pressure. We report the pressure-induced structural and magnetic evolution of the antiferromagnetic insulator CaMn$_2$Sb$_2$. Single-crystal X-ray diffraction reveals a first-order phase transition near 5.4 GPa from a trigonal P-3m1 structure to a monoclinic P2$_1$/m phase, accompanied by a ~7% volume collapse. Residual electron density analysis at intermediate pressures reveals charge localization along Mn-Sb chains, signaling electronic instability preceding the structural transition. Bonding analysis indicates anisotropic Mn-Sb orbital reconfiguration under pressure, driving a distorted square-pyramidal geometry. Neutron scattering confirms the transition and identifies a pressure-induced incommensurate magnetic order, distinct from the ambient antiferromagnetic state. In the monoclinic phase, zigzag Mn chains exhibit antiferromagnetic coupling along the ac-plane, enabled by enhanced orbital overlap. These results establish CaMn$_2$Sb$_2$ as a model system for studying the coupling of structural distortion, charge redistribution, and magnetic order in layered Mn pnictides under pressure.

cond-mat.str-el↗

arXiv2025

Robust superzone gap opening in incommensurate antiferromagnetic semimetal EuAg$_4$Sb$_2$ under in-plane magnetic field

The interplay between magnetism and charge transport in semimetals has emerged as a fertile ground for discovering novel electronic phenomena. A notable example is the recent discovery of electronic commensuration arising from a spin moiré superlattice (SMS), realized as double-q spin modulation in the antiferromagnetic semimetal EuAg$_4$Sb$_2$. Here, we investigate the in-plane magnetic-field tunability of the SMS using neutron scattering, magnetic and transport measurements. We reveal an incommensurate noncollinear cycloidal magnetic ground state. Temperature-field phase diagrams constructed with field tilting uncover multiple spin-reoriented phases, suggesting the critical role of in-plane field components in driving magnetic transitions. Despite substantial spin reorientation of the double-q phase, we observe a persistent gap opening, evidenced by strong suppression in both Hall and longitudinal conductivities. Model calculations attribute this robustness to the stability of SMS under tilting fields. Our results establish EuAg$_4$Sb$_2$ as a tunable platform for exploring spin-texture-driven superzone gap opening in electronic states.

cond-mat.str-el↗

arXiv2024

Quantum entanglement of XY-type spin dimers in Shastry-Sutherland lattice

We report a comprehensive study on the origin of the enigmatic disordered ground state within the Shastry-Sutherland lattice, BaCe$_2$ZnS$_5$, at low temperatures. The magnetization and heat capacity data show a lack of magnetic ordering down to 73 mK. We deploy a localized spin dimer model which can accurately reproduce the dynamic structure factor of the neutron data, magnetization and heat capacity data. Remarkably, the intra-dimer exchange interaction shows strong XY-type anisotropy and the ground state of BaCe$_2$ZnS$_5$ is in an entangled state $(|\uparrow\uparrow> - |\downarrow\downarrow>)/\sqrt{2}$. This is in contrast to the singlet dimer state that is obtained for Heisenberg interactions. These results confirm that BaCe$_2$ZnS$_5$ is in a quantum paramagnet state consisting of entangled spin dimer states.

cond-mat.str-el↗

arXiv2023

Incommensurate Spiral Spin Order in CaMn$_2$Bi$_2$ observed via High Pressure Neutron Diffraction

High pressure neutron diffraction is employed to investigate the magnetic behavior of CaMn$_2$Bi$_2$ in extreme conditions. In contrast to antiferromagnetic ordering on Mn atoms reported at ambient pressure, our results reveal that at high pressure, incommensurate spiral spin order emerges due to the interplay between magnetism on the Mn atoms and strong spin-orbit coupling on the Bi atoms: sinusoidal spin order is observed at pressures as high as 7.4 GPa. Competing antiferromagnetic order is observed at different temperatures in the partially frustrated lattice. This research provides a unique toolbox for conducting experimental magnetic and spin dynamics studies on magnetic quantum materials via high pressure neutron diffraction.

cond-mat.mtrl-sci↗

arXiv2023

Field-Induced Partial Disorder in a Shastry-Sutherland Lattice

A 2-Q antiferromagnetic order of the ferromagnetic dimers was found below TN = 2.9 K in the Shastry-Sutherland lattice BaNd2ZnS5 by single crystal neutron diffraction. The magnetic order can be understood by the orthogonal arrangement of local Ising Nd spins, identified by polarized neutrons. A field was applied along [1 -1 0] to probe the observed metamagnetic transition in the magnetization measurement. The field decouples two magnetic sublattices corresponding to the propagation vectors q1= (0.5, 0.5, 0) and q2= (-0.5, 0.5, 0), respectively. Each sublattice shows a stripe order with a Neel-type arrangement in each single layer. The stripe order with q1 remains nearly intact up to 6 T, while the other one with q2 is suppressed at a critical field Hc ~1.7 T, indicating a partial disorder. The Hc varies with temperature and is manifested in the H-T phase diagram constructed by measuring the magnetization in BaNd2ZnS5.

cond-mat.str-el↗

arXiv2023

Tiny Sc allows the chains to rattle: Impact of Lu and Y doping on the charge density wave in ScV$_6$Sn$_6$

The kagome metals display an intriguing variety of electronic and magnetic phases arising from the connectivity of atoms on a kagome lattice. A growing number of these materials with vanadium kagome nets host charge density waves (CDWs) at low temperatures including ScV$_6$Sn$_6$, CsV$_3$Sb$_5$, and V$_3$Sb$_2$. Curiously, only the Sc version of the $R$V$_6$Sn$_6$ HfFe$_6$Ge$_6$-type materials hosts a CDW ($R = $Gd-Lu, Y, Sc). In this study we investigate the role of rare earth size in CDW formation in the $R$V$_6$Sn$_6$ compounds. Magnetization measurements on our single crystals of (Sc,Lu)V$_6$Sn$_6$ and (Sc,Y)V$_6$Sn$_6$ establish that the CDW is suppressed by substitution of Sc by larger Lu or Y. Single crystal x-ray diffraction reveals that compressible Sn-Sn bonds accommodate the larger rare earth atoms within loosely packed $R$-Sn-Sn chains without significantly expanding the lattice. We propose that Sc provides the extra room in these chains crucial to CDW formation in ScV$_6$Sn$_6$. Our rattling chain model explains why both physical pressure and substitution by larger rare earths hinder CDW formation despite opposite impacts on lattice size. We emphasize the cooperative effect of pressure and rare earth size by demonstrating that pressure further suppresses the CDW in a Lu-doped ScV$_6$Sn$_6$ crystal. Our model not only addresses why a CDW only forms in the $R$V$_6$Sn$_6$ materials with tiny Sc, it also advances to our understanding of why unusual CDWs form in the kagome metals.

cond-mat.str-el↗

arXiv2023

Non-centrosymmetric Sr$_{2}$IrO$_{4}$ obtained under High Pressure

Sr$_{2}$IrO$_{4}$ with strong spin-orbit coupling (SOC) and Hubbard repulsion (U) hosts Mott insulating states. The similar crystal structure, magnetic and electronic properties, particularly the $d$-wave gap observed in Sr$_{2}$IrO$_{4}$ enhanced the analogies to cuprate high-$T_{c}$ superconductor, La$_{2}$CuO$_{4}$. The incomplete analogy was due to the lack of broken inversion symmetry phases observed in Sr$_{2}$IrO$_{4}$. Here, under high pressure and high temperature conditions, we report a non-centrosymmetric Sr$_{2}$IrO$_{4}$. The crystal structure and its noncentrosymmetric character were determined by single crystal X-ray diffraction and high-resolution scanning transmission electron microscopy (HR-STEM). The magnetic characterization confirms the Ir$^{4+}$ with $S$ = 1/2 at low temperature in Sr$_{2}$IrO$_{4}$ with magnetic ordering occurred at around 86 K, where a larger moment is observed than the ambient pressure Sr$_{2}$IrO$_{4}$. Moreover, the resistivity measurement shows three-dimensional Mott variable-range hopping existed in the system. This non-centrosymmetric Sr$_{2}$IrO$_{4}$ phase appears to be a unique material to offer further understanding of high-$T_{c}$ superconductivity.

cond-mat.str-el↗

arXiv2022

Single crystal synthesis and magnetic properties of a Shastry-Sutherland lattice compound BaNd2ZnS5

Single crystals of a Shastry-Sutherland magnetic semiconductor, BaNd2ZnS5, were synthesized through a high-temperature solution growth technique. Physical properties were characterized by powder and single crystal x-ray diffraction, temperature- and field-dependent magnetization, and temperature-dependent specific heat measurements. BaNd2ZnS5 orders antiferromagnetically at 2.9 K, with magnetic moments primarily aligned within the ab-plane. Magnetic isothermal measurements show metamagnetic transitions at ~ 15 kOe for the [110] direction and ~ 21 kOe for the [100] direction. Estimated magnetic entropy suggests a double ground state for each Nd ion.

cond-mat.mtrl-sci↗

arXiv2022

Charge density wave in kagome lattice intermetallic ScV6Sn6

Materials hosting kagome lattices have drawn interest for the diverse magnetic and electronic states generated by geometric frustration. In the $A$V$_3$Sb$_5$ compounds ($A$ = K, Rb, Cs), stacked vanadium kagome layers give rise to unusual charge density waves (CDW) and superconductivity. Here we report single-crystal growth and characterization of ScV$_6$Sn$_6$, a hexagonal HfFe$_6$Ge$_6$-type compound that shares this structural motif. We identify a first-order phase transition at 92 K. Single crystal X-ray and neutron diffraction reveal a charge density wave modulation of the atomic lattice below this temperature. This is a distinctly different structural mode than that observed in the $A$V$_3$Sb$_5$ compounds, but both modes have been anticipated in kagome metals. The diverse HfFe$_6$Ge$_6$ family offers more opportunities to tune ScV$_6$Sn$_6$ and explore density wave order in kagome lattice materials.

cond-mat.str-el↗

arXiv2022

Unusual electrical and magnetic properties in layered EuZn2As2

Eu-based compounds often exhibit unusual magnetism, which is critical for nontrivial topological properties seen in materials such as EuCd2As2. We investigate the structure and physical properties of EuZn2As2 through measurements of the electrical resistivity, Hall effect, magnetization, and neutron diffraction. Our data show that EuZn2As2 orders antiferromagnetically with an A-type spin configuration below TN = 19 K. Surprisingly, there is strong evidence for dominant ferromagnetic fluctuations above TN, as reflected by positive Curie-Weiss temperature and extremely large negative magnetoresistance (MR) between TN and Tfl » 200 K. Furthermore, the angle dependence of the MRab indicates field-induced spin reorientation from the ab-plane to a direction approximately 45° from the ab plane. Compared to EuCd2As2, the doubled TN and Tfl make EuZn2As2 a better platform for exploring topological properties in both magnetic fluctuation (TN < T < Tfl) and ordered (T < TN) regimes.

cond-mat.mtrl-sci↗

arXiv2021

Anomalous Hall effect in distorted kagome magnets (Nd, Sm)Mn$_6$Sn$_6$

We report magnetic and electrical properties for single crystals of NdMn$_6$Sn$_6$ and SmMn$_6$Sn$_6$. They crystallize into a structure which has distorted, Mn-based kagome lattices, compared to the pristine kagome lattices in heavy-rare-earth-bearing RMn$_6$Sn$_6$ compounds. They are hightemperature ferromagnets of which the R moment is parallel with the Mn moment. We observed a large intrinsic anomalous Hall effect (AHE) that is comparable to the ferrimagnetic, heavy-R siblings in a wide range of temperature. We conclude that their intrinsic AHE is stemming from the Mn-based kagome lattice, just as in the heavy RMn$_6$Sn$_6$.

cond-mat.str-el↗

arXiv2021

Annihilation and Control of Chiral Domain Walls with Magnetic Fields

The control of domain walls is central to nearly all magnetic technologies, particularly for information storage and spintronics. Creative attempts to increase storage density need to overcome volatility due to thermal fluctuations of nanoscopic domains and heating limitations. Topological defects, such as solitons, skyrmions, and merons, may be much less susceptible to fluctuations, owing to topological constraints, while also being controllable with low current densities. Here, we present the first evidence for soliton/soliton and soliton/antisoliton domain walls in the hexagonal chiral magnet Mn1/3NbS2 that respond asymmetrically to magnetic fields and exhibit pair-annihilation. This is important because it suggests the possibility of controlling the occurrence of soliton pairs and the use of small fields or small currents to control nanoscopic magnetic domains. Specifically, our data suggest that either soliton/soliton or soliton/antisoliton pairs can be stabilized by tuning the balance between intrinsic exchange interactions and long-range magnetostatics in restricted geometries

cond-mat.mes-hall↗