arXiv subjects

Tim B. Eldred

Publications and source records attributed to Tim B. Eldred.

3 recordsLinked to original sources

arXiv2026

Proximity Magnetism in Mn(Bi,Sb)2Te4-(Bi,Sb)2Te3/MnTe Natural Heterostructures

Magnetic topological insulators and their heterostructures provide great opportunities in coupling band topology with nontrivial spin configuration for enhanced spintronic device performance as well as designing totally new magnetoelectric systems and functionalities. We find that Mn interdiffusion from MnTe when interfaced with (Bi,Sb)2Te3 stabilizes as self-organized Mn(Bi,Sb)2Te4 septuple lamellae amongst alternating (Bi,Sb)2Te3 quintuple layers, as observed using scanning transmission electron microscopy and depth-sensitive polarized neutron reflectometry. We further demonstrate a valuable combination of magnetic and topological orders in these naturally formed Mn(Bi,Sb)2Te4-(Bi,Sb)2Te3 heterostructures that are exchange coupled with MnTe. Magnetotransport experiments and quantum magnetism simulations reveal that, above its own Neel temperature TN of 20 K, Mn(Bi,Sb)2Te4 mediates the exchange field leading to an anomalous Hall effect at the (Bi,Sb)2Te3/MnTe interface, with an enhanced interfacial TN exceeding 200 K. This novel magnetic interface in turn allows a robust and deterministic spin-orbit torque switching without an external magnetic field at a low critical current density of 300 kA cm-2. The antiferromagnetically coupled architecture of Mn(Bi,Sb)2Te4-(Bi,Sb)2Te3/MnTe, featuring unique magnetic and topological proximity effects across a chalcogenide backbone, is rich in fundamental interface physics and holds potential for practical applications in spintronics.

cond-mat.mtrl-sci↗

arXiv2022

Strain-tunable Berry curvature in quasi-two-dimensional chromium telluride

Magnetic transition metal chalcogenides form an emerging platform for exploring spin-orbit driven Berry phase phenomena owing to the nontrivial interplay between topology and magnetism. Here we show that the anomalous Hall effect in pristine Cr2Te3 thin films manifests a unique temperature-dependent sign reversal at nonzero magnetization, resulting from the momentum-space Berry curvature as established by first-principles simulations. The sign change is strain tunable, enabled by the sharp and well-defined substrate/film interface in the quasi-two-dimensional Cr2Te3 epitaxial films, revealed by scanning transmission electron microscopy and depth-sensitive polarized neutron reflectometry. This Berry phase effect further introduces hump-shaped Hall peaks in pristine Cr2Te3 near the coercive field during the magnetization switching process, owing to the presence of strain-modulated magnetic domains. The versatile interface tunability of Berry curvature in Cr2Te3 thin films offers new opportunities for topological electronics.

cond-mat.mtrl-sci↗

arXiv2021

Sub-Unit Cell Spatial Resolution of Phase and Polarization Mapping in Scanning Electron Diffraction

Diffraction analysis in four dimensional scanning transmission electron microscopy now enables the mapping of local structures including symmetry, strain, and polarization of materials. However, measuring the distribution of these configurations at the unit cell level remains a challenge because most analysis methods require the diffraction disks to be separated, limiting the electron probe sizes to be larger than a unit cell. Here we show improved spatial resolution in mapping the polarization displacement and phases of BaTiO3 sampled at a rate equivalent to the size of the projected unit cells using 4DSTEM. This improvement in spatial resolution is accomplished by masking out the overlapping regions in partially overlapped CBED patterns. By reducing the probe size to the order of single projected unit cells in size, the fluctuations of symmetry and structure inside the rhombohedral symmetry nanoregions inside of tetragonal domains can be observed. With the mapping performed at the unit cell resolution the nano-sized rhombohedral domains break down with local fluctuation, showing different character at different length scales.

cond-mat.mtrl-sci↗