arXiv subjects

Cory D. Cress

Publications and source records attributed to Cory D. Cress.

7 recordsLinked to original sources

arXiv2026

Conductivity scaling of the anomalous Hall effect in the altermagnetic semiconductor α-MnTe

α-MnTe is a prototypical altermagnet exhibiting a strong anomalous Hall effect (AHE), despite having a nearly vanishing magnetization. Lately, sample-to-sample variations of the amplitude of the AHE have raised concerns of a possible defect related origin, especially in thin films. Here, we study the AHE in α-MnTe films grown on SrF2 that have the crystal structure and m'm'm magnetic point group symmetry expected for bulk. By studying the scaling of the AHE with conductivity for those films and previously reported measurements in the literature, we find that sample-to-sample variations are well explained by a scaling law consistent with a hopping origin. Importantly, a comparison with other magnetic semiconductors reveals the colossal amplitude of the AHE of α-MnTe compared to its measured spontaneous magnetization from magnetometry and polarized neutron reflectivity. Our findings address the important fundamental question of the origin of the AHE of α-MnTe and further demonstrate the potential of altermagnets as promising spintronic materials.

cond-mat.str-el↗

arXiv2025

Non-Altermagnetic Origin of Exchange Bias Behaviors in Incoherent RuO$_2$/Fe Bilayer Heterostructures

Initially identified as a promising altermagnetic (AM) candidate, rutile RuO$_2$ has since become embroiled in controversy due to contradictory findings of modeling and measurements of the magnetic properties of bulk crystals and thin films. For example, despite observations of a bulk non-magnetic state using density functional theory, neutron scattering, and muon spin resonance measurements, patterned RuO$_2$ Hall bars and film heterostructures display magnetotransport signatures of magnetic ordering. Among the characteristics routinely cited as evidence for AM is the observation of exchange bias (EB) in an intimately contacted Fe-based ferromagnetic (FM) layer, which can arise due to interfacial coupling with a compensated antiferromagnet. Within this work, the origins of this EB coupling in Ru-capped RuO$_2$/Fe bilayers are investigated using polarized neutron diffraction, polarized neutron reflectometry, cross-sectional transmission electron microscopy, and super conducting quantum interference device measurements. These experiments reveal that the EB behavior is driven by the formation of an iron oxide interlayer containing Fe$_3$O$_4$ that undergoes a magnetic transition and pins interfacial moments within Fe at low temperature. These findings are confirmed by comparable measurements of Ni-based heterostructures, which do not display EB coupling, as well as magnetometry of additional Fe/Ru bilayers that display oxide-driven EB coupling despite the absence of the epitaxial RuO$_2$ layer. While these results do not directly refute the possibility of AM ordering in RuO$_2$ thin films, they reveal that EB, and related magnetotransport phenomena, cannot alone be considered evidence of this characteristic in the rutile structure due to interfacial chemical disorder.

cond-mat.mtrl-sci↗

arXiv2025

Effects of altermagnetic order, strain and doping in RuO$_2$

RuO$_2$, one of the most widely studied transition metal oxides, was recently predicted to host a novel form of collinear magnetic order referred to as altermagnetism. In this study we combine experiment (reflectance, transmittance, ellipsometry and Raman measurements) and first-principles calculations to elucidate the potential role of altermagnetic order, strain and doping on the optical and vibrational properties of RuO$_2$ grown on TiO$_2$ (001), (101) and (110) substrates. Our combined experimental and theoretical results point toward a nonmagnetic ground state as the most consistent description of the optical and vibrational properties of bulk RuO$_2$. RuO$_2$ strained to TiO$_2$ (001) remains nonmagnetic in our calculations. Straining to TiO$_2$ (110) stabilizes ferromagnetic and altermagnetic states that are nearly degenerate and both lower in energy than the nonmagnetic state. The relative energetic ordering of these states is highly sensitive to the level of strain and the choice of exchange-correlation approximation.

cond-mat.mtrl-sci↗

arXiv2025

Nitrogen-Vacancy Magnetometry of Edge Magnetism in WS2 Flakes

Two-dimensional (2D) magnets are of significant interest both as a platform for exploring novel fundamental physics and for their potential in spintronic and optoelectronic devices. Recent bulk magnetometry studies have indicated a weak ferromagnetic response in WS2, and theoretical predictions suggest edge-localized magnetization in flakes with partial hydrogenation. Here, we use room-temperature wide-field quantum diamond magnetometry to image pristine and Fe-implanted WS2 flakes of varying thicknesses (45-160 nm), exfoliated from bulk crystals and transferred to NV-doped diamond substrates. We observe direct evidence of edge-localized stray magnetic fields, which scale linearly with applied external magnetic field (4.4-220 mT), reaching up to 4.7 uT. The edge signal shows a limited dependence on the flake thickness, consistent with dipolar field decay and sensing geometry. Magnetic simulations using five alternative models favor the presence of edge magnetization aligned along an axis slightly tilted from the normal to the WS2 flake plane, consistent with spin canting in antiferromagnetically coupled edge states. Our findings establish WS2 as a promising platform for edge-controlled 2D spintronics.

cond-mat.mes-hall↗

arXiv2025

Hydrated Cable Bacteria Exhibit Protonic Conductivity Over Long Distances

This study presents the direct measurement of proton transport along filamentous Desulfobulbaceae, or cable bacteria. Cable bacteria are filamentous multicellular microorganisms that have garnered much interest due to their ability to serve as electrical conduits, transferring electrons over several millimeters. Our results indicate that cable bacteria can also function as protonic conduits because they contain proton wires that transport protons at distances greater than 100 um. We find that protonic conductivity (σP) along cable bacteria varies between samples and is measured as high as 114 +/- 28 uS cm^-1 at 25-degrees C and 70-percent relative humidity (RH). For cable bacteria, the protonic conductance (GP) and σP are dependent upon the RH, increasing by as much as 26-fold between 60-percent and 80-percent RH. This observation implies that proton transport occurs via the Grotthuss mechanism along water associated with cable bacteria, forming proton wires. In order to determine σP and GP along cable bacteria, we implemented a protocol using a modified transfer-printing technique to deposit either palladium interdigitated protodes (IDP), palladium transfer length method (TLM) protodes, or gold interdigitated electrodes(IDE) on top of cable bacteria. Due to the relatively mild nature of the transfer-printing technique, this method should be applicable to a broad array of biological samples and curved materials. The observation of protonic conductivity in cable bacteria presents possibilities for investigating the importance of long-distance proton transport in microbial ecosystems and to potentially build biotic or biomimetic scaffolds to interface with materials via proton-mediated gateways or channels.

physics.bio-ph↗

arXiv2022

High-speed metamagnetic resistive switching of FeRh through Joule heating

Due to its proximity to room temperature and demonstrated high degree of temperature tunability, the metamagnetic ordering transition in FeRh is attractive for novel high-performance computing devices seeking to use magnetism as the state variable. We demonstrate electrical control of the transition via Joule heating in FeRh wires. Finite element simulations based on abrupt state transition within each domain result in a globally smooth transition that agrees with the experimental findings and provides insight into the thermodynamics involved. We measure a 150 K decrease in transition temperature with currents up to 60 mA, limited only by the dimensions of the device. The sizeable shift in transition temperature scales with current density and wire length, suggesting the absolute resistance and heat dissipation of the substrate are also important. The FeRh phase change is evaluated by pulsed I-V using a variety of bias conditions. We demonstrate high speed (~ ns) memristor-like behavior and report device performance parameters such as switching speed and power consumption that compare favorably with state-of-the-art phase change memristive technologies.

cond-mat.mes-hall↗

arXiv2010

Correlation between structure and electrical transport in ion-irradiated graphene grown on Cu foils

Graphene grown by chemical vapor deposition and supported on SiO2 and sapphire substrates was studied following controlled introduction of defects induced by 35 keV carbon ion irradiation. Changes in Raman spectra following fluences ranging from 10^12 cm^-2 to 10^15 cm^-2 indicate that the structure of graphene evolves from a highly ordered layer, to a patchwork of disordered domains, to an essentially amorphous film. These structural changes result in a dramatic decrease in the Hall mobility by orders of magnitude while, remarkably, the Hall concentration remains almost unchanged, suggesting that the Fermi level is pinned at a hole concentration near 1x10^13 cm^-2. A model for scattering by resonant scatterers is in good agreement with mobility measurements up to an ion fluence of 1x10^14 cm^-2.

cond-mat.mtrl-sci↗