arXiv subjects

A. E. Hall

Publications and source records attributed to A. E. Hall.

6 recordsLinked to original sources

arXiv2025

Magnetism in $M_{1/3}$NbS$_2$ ($M$ = Fe, V, Mn): insight into intercalated transition-metal dichalcogenides using $μ$SR

We present the results of muon-spin relaxation ($μ$SR) measurements of the static and dynamic magnetism of $M_{1/3}$NbS$_2$ ($M$ = Fe, V, Mn), three intercalated transition-metal dichalcogenides. Transitions to long-range magnetic order are observed in all three materials and local magnetic fields at muon sites are compared to dipole field calculations. Measurements on Fe$_{1/3}$NbS$_2$ capture the evolution of two coexisting magnetic phases. In V$_{1/3}$NbS$_2$ we observe a peak in the dynamic response at $9$ K, coincident with previous reports of a possible low-temperature phase transition. The observation of high-frequency muon precession in Mn$_{1/3}$NbS$_2$ suggests the existence of an additional muon site that implies a difference in electronic energy landscape compared to the other materials in the series. Taken together, this demonstrates that the change in intercalant species drives significant variations in magnetism, highlighting the $M_{1/3}$NbS$_2$ ($M$ = Fe, V, Mn) series as an ideal group of materials for investigating a wide range of magnetic phenomena.

cond-mat.str-el↗

arXiv2023

The Double-$Q$ Ground State with Topological Charge Stripes in the Skyrmion Candidate $\text{GdRu}_{\text{2}}\text{Si}_{\text{2}}$

$\text{GdRu}_{\text{2}}\text{Si}_{\text{2}}$ is a centrosymmetric magnet in which a skyrmion lattice has recently been discovered. Here, we investigate the magnetic structure of the zero field ground state using neutron diffraction on single crystal and polycrystalline $^{\text{160}}\text{GdRu}_{\text{2}}\text{Si}_{\text{2}}$. In addition to observing the principal propagation vectors $\mathbf{q}_{1}$ and $\mathbf{q}_{2}$, we discover higher order magnetic satellites, notably $\mathbf{q}_{1} + 2\mathbf{q}_{2}$. The appearance of these satellites are explained within the framework of a new double-$Q$ constant-moment solution. Using powder diffraction we implement a quantitative refinement of this model. This structure, which contains vortexlike motifs, is shown to have a one-dimensional topological charge density.

cond-mat.str-el↗

arXiv2022

Giant topological and planar Hall effect in Cr$_{1/3}$NbS$_{2}$

Cr$_{1/3}$NbS$_{2}$ is a transition metal dichalcogenide that has been of significant interest due to its ability to host a magnetic chiral soliton lattice. Conventional and planar Hall measurements provide valuable insight into the detection of exotic spin structures in chiral magnets. We show that the presence of a giant planar Hall effect can be attributed to a tilted soliton lattice in Cr$_{1/3}$NbS$_{2}$. Our detailed angular dependent study shows the planar Hall effect and anisotropic magnetoresistance are intrinsically linked in complex non-coplanar magnets. From the conventional Hall signal we show the presence of a giant unconventional, likely topological Hall component, that is the fingerprint of non-coplanar spin textures.

cond-mat.str-el↗

arXiv2022

Energy-gap driven low-temperature magnetic and transport properties in Cr$_{1/3}M$S$_2$ ($M$ = Nb or Ta)

The helimagnets Cr$_{1/3}M$S$_2$ ($M$ = Nb or Ta) have attracted renewed attention due to the discovery of a chiral soliton lattice (CSL) stabilized in an applied magnetic field, but reports of unusual low-temperature transport and magnetic properties in this system lack a unifying explanation. Here we present electronic structure calculations that demonstrate the materials are half-metals. There is also a gap-like feature (width in range 40-100 meV) in the density of states of one spin channel. This electronic structure explains the low-temperature electronic and magnetic properties of Cr$_{1/3}M$S$_2$ ($M$ = Nb or Ta), with the gap-like feature particularly important for explaining the magnetic behavior. Our magnetometry measurements confirm the existence of this gap. Dynamic spin fluctuations driven by excitations across this gap are seen over a wide range of frequencies (0.1 Hz to MHz) with AC susceptibility and muon-spin relaxation ($μ^+$SR) measurements. We show further how effects due to the CSL in Cr$_{1/3}$NbS$_2$, as detected with $μ^+$SR, dominate over the gap-driven magnetism when the CSL is stabilized as the majority phase.

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arXiv2020

Megahertz dynamics in skyrmion systems probed with muon-spin relaxation

We present longitudinal-field muon-spin relaxation (LF $μ$SR) measurements on two systems that stabilize a skyrmion lattice (SkL): Cu$_2$OSeO$_3$, and Co$_x$Zn$_y$Mn$_{20-x-y}$ for $(x,y)~=~(10,10)$, $(8,9)$ and $(8,8)$. We find that the SkL phase of Cu$_2$OSeO$_3$ exhibits emergent dynamic behavior at megahertz frequencies, likely due to collective excitations, allowing the SkL to be identified from the $μ$SR response. From measurements following different cooling protocols and calculations of the muon stopping site, we suggest that the metastable SkL is not the majority phase throughout the bulk of this material at the fields and temperatures where it is often observed. The dynamics of bulk Co$_8$Zn$_9$Mn$_3$ are well described by $\simeq~2$ GHz excitations that reduce in frequency near the critical temperature, while in Co$_8$Zn$_8$Mn$_4$ we observe similar behavior over a wide range of temperatures, implying that dynamics of this kind persist beyond the SkL phase.

cond-mat.str-el↗

arXiv2020

Structure and magnetism of the skyrmion hosting family GaV$_4$S$_{8-y}$Se$_y$ with low levels of substitutions between $0 \leq y \leq 0.5$ and $7.5 \leq y\leq 8$

Polycrystalline members of the GaV$_4$S$_{8-y}$Se$_y$ family of materials with small levels of substitution between $0 \leq y \leq 0.5$ and $7.5 \leq y\leq 8$ have been synthesized in order to investigate their magnetic and structural properties. Substitutions to the skyrmion hosting parent compounds GaV$_4$S$_8$ and GaV$_4$Se$_8$, are found to suppress the temperature of the cubic to rhombohedral structural phase transition that occurs in both end compounds and to create a temperature region around the transition where there is a coexistence of these two phases. Similarly, the magnitude of the magnetization and temperature of the magnetic transition are both suppressed in all substituted compounds until a glassy-like magnetic state is realized. There is evidence from the $ac$ susceptibility data that skyrmion lattices with similar dynamics to those in GaV$_4$S$_8$ and GaV$_4$Se$_8$ are present in compounds with very low levels of substitution, $0 < y< 0.2$ and $7.8 < y < 8$, however, these states vanish at higher levels of substitution. The magnetic properties of these substituted materials are affected by the substitution altering exchange pathways and resulting in the creation of increasingly disordered magnetic states.

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