Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session S55: Skyrmions and Chiral Spin Textures in Bulk Materials IIFocus
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Sponsoring Units: GMAG Chair: Sang-Wook Cheong, Rutgers University Room: Room 305 |
Thursday, March 9, 2023 8:00AM - 8:36AM |
S55.00001: Magnetic Chirality Invited Speaker: Sang-Wook Cheong Chirality (C) with all broken mirror symmetries, combined with any spatial rotations, matters ubiquitously from DNA functionality, vine climbing, to the piezoelectricity of quartz crystals. Magnetic chirality means chirality in spin ordered states or (atomic-scale or mesoscopic) spin textures. Magnetic chirality does not change with time reversal operation, and chirality prime (C') means that time reversal symmetry in addition to all mirror symmetries, combined with any spatial rotations, are broken. In the case of C', there exist two kinds: type-I C' with unbroken "space inversion x time reversal" and type-II C' with broken "space inversion x time reversal". Four examples of magnetic chirality will be discussed: helical spin state, magnetic toroidal moment combined with canted moment, magnetic quadruple moment combined with alternating canted moments, and Bloch-type skyrmions. We will also discuss a few examples of type-I C' type-II C', and the emergent physical phenomena of C and C' such as anomalous Hall effect and linear magnetoelectricity. Some of these exotic phenomena have been recently observed, and many of them need to be experimentally confirmed. |
Thursday, March 9, 2023 8:36AM - 8:48AM |
S55.00002: Electronic chiralization as an indicator of the anomalous Hall effect in unconventional magnetic systems Hua Chen The anomalous Hall effect (AHE) can appear in certain antiferromagnetic metals when it is allowed by symmetry. Since the net magnetization is usually small in such anomalous Hall antiferromagnets, it is useful to have other physical indicators of the AHE that have the same symmetry properties as the latter and can be conveniently measured and calculated. Here we propose such indicators named as electronic chiralization (EC), which are constructed using spatial gradients of spin and charge densities in general periodic crystals, and can potentially be measured directly by scattering experiments. Such constructions particularly reveal the important role of magnetic charge in the AHE in unconventional magnetic systems with vanishing net magnetization. Guided by the EC we give two examples of the AHE when magnetic charge is explicitly present: A minimum honeycomb model inspired by the magnetic-charge-ordered phase of kagome spin ice, and skew scattering of two-dimensional Dirac electrons by magnetic charge. |
Thursday, March 9, 2023 8:48AM - 9:00AM Author not Attending |
S55.00003: Observation of Néel-type skyrmions in Mn2-xZnxSb single crystals. Suzanne G te Velthuis, Yue Li, Charudatta Phatak, Md Rafique Un Nabi, Jin Hu Mn2-xZnxSb alloys are layered tetragonal materials for which previous work has suggested they exhibit tuneable nontrivial topological magnetism [1]. While the parent compound has a centrosymmetric tetragonal lattice and ferrimagnetic order, with high Zn doping a layered structure and ferromagnetic order develops. We have studied single crystals with high Zn doping (x = 0.81, 0.85) with magneto-optical Kerr effect (MOKE) microscopy and Lorentz TEM as a function of temperature. We observe magnetic stripe domains at low field that evolve into skyrmions at higher field. Lorenz TEM imaging determined that they are Néel-type skyrmions, which is not commonly observed in bulk materials. There is no significant change in the domain behavior, even when passing the spin-reorientation transition [1] indicating that the out-of-plane magnetic component still dominates at low temperatures. |
Thursday, March 9, 2023 9:00AM - 9:12AM |
S55.00004: Multi-step topological phase transitions among meron/antimeron and skyrmion crystals in a centrosymmetric magnet Haruto Yoshimochi, Rina Takagi, Jiwon Ju, Nguyen D Khanh, Hikaru Saito, Hajime Sagayama, Hironori Nakao, Shinichi Itoh, Yoshinori Tokura, Taka-hisa Arima, Satoru Hayami, Taro Nakajima, Shinichiro Seki Topological swirling spin textures, such as skyrmions and merons, have attracted much attention as a candidate for potential high-density information bits. |
Thursday, March 9, 2023 9:12AM - 9:24AM |
S55.00005: Chiral spin texture in the anomalous Hall antiferromagnet CoNb3S6 Ben Zager, Kemp Plumb, Paul Steadman, Raymond Fan CoNb3S6 (CNS) is an intercalated transition metal dichalcogenide exhibiting a large anomalous Hall effect (AHE) that cannot be explained by the collinear magnetic order previously observed by neutron diffraction. Thus, complex chiral, non-collinear, or non-coplanar spin orders have all been proposed as explanations for the observed large AHE in CNS. We carried out resonant elastic x-ray scattering (REXS) at the Co L3 edge to obtain a complete description of the magnetic ordering in CNS. Using full linear polarization analysis, we found that the magnetic order is consistent with a single-Q multi-domain order rather than a multi-Q order. We also observed satellite peaks around the collinear wavevector, indicating a ∼30 nm uniaxial modulation of the collinear order. These satellites exhibit a circular dichroism, indicating a chiral magnetic structure. These results suggest that a long-range chiral spin texture provides the necessary symmetry-breaking mechanism for the large AHE in CNS. |
Thursday, March 9, 2023 9:24AM - 9:36AM |
S55.00006: High resolution magnetic neutron diffraction study of the chiral lattice antiferromagnet CoNb3S6 Eleanor M Clements, Peter Siegfried, Andrew L Balk, Hari Bhandari, John W Freeland, Scott A Crooker, Filip Ronning, Lekh Poudel, John F Mitchell, Igor I Mazin, Huibo Cao, Jeffrey W Lynn, Nirmal J Ghimire CoNb3S6 is a chiral lattice antiferromagnet which belongs to a class of intercalated transition metal dichalcogenides known for complex magnetic textures, nontrivial band topology, and superconductivity. Previous neutron diffraction measurements below the Néel temperature (TN ~ 26 K) pointed to a collinear spin arrangement in this material. However, a more recent discovery of a large anomalous Hall effect (AHE), three orders of magnitude large than that explained by its weak field-induced magnetism, raises questions about the true nature of its magnetic ordering. Here, we present results on high resolution magnetic neutron diffraction and magnetic circular dichroism (MCD) measurements to unravel the details of its magnetic structure. We identify a long wavelength incommensurate magnetic structure with moments lying in the ab plane. Higher harmonic peaks are absent down to 2 K, consistent with a helical ground state. The results are complemented by MCD data suggesting changes in the underlying magnetic chirality in an applied field, which may help explain the origin of the large AHE. |
Thursday, March 9, 2023 9:36AM - 9:48AM |
S55.00007: Topological Thermal Hall Effect of Magnons in Magnetic Skyrmion Lattice Minoru Yamashita, Masatoshi Akazawa, Hyun-Yong Lee, Hikaru Takeda, Yuri Fujima, Taka-hisa Arima, Yusuke Tokunaga, Jung Hoon Han Topological transports of fermions are governed by the Chern numbers of the energy bands lying below the Fermi energy. For bosons, e.g. phonons and magnons in a crystal, topological transport is dominated by the Chern number of the lowest energy band when the band gap is comparable to the thermal energy. Here, we demonstrate the presence of topological transport by bosonic magnons in a lattice of magnetic skyrmions - topological defects formed by a vortex-like texture of spins. We find a distinct thermal Hall signal in the magnetic skyrmion phase of an insulating polar magnet GaV4Se8, identified as the topological thermal Hall effect of magnons governed by the Chern number of the lowest energy band of the magnons in a triangular lattice of magnetic skyrmions. Our findings lay a foundation for studying topological phenomena of other bosonic excitations through thermal Hall probe. |
Thursday, March 9, 2023 9:48AM - 10:00AM Author not Attending |
S55.00008: Investigations of magnetic spin-textures in the antiskyrmion compound Mn1.4PtSn by complementary microscopy and scattering experiments using LTEM and REXS Moritz Winter, Marein Rahn, Daniel Wolf, Sebastian Schneider, Manuel Valvidares, Chandra Shekhar, Praveen Vir, Toni Helm, Barat Achinuq, Horia Popescu, Nicolas Jaouen, Alexander Tahn, Gerrit Van der Laan, Thorsten Hesjedal, Bernd Rellinghaus, Claudia Felser More than a decade has passed since the first experimental evidence of magnetic Bloch-type skyrmions in MnSi [1]. Meanwhile, driven by basic research interests in topologically protected magnetic nanostructures and their potential for applications in future magnetic memory devices, skyrmions and related magnetic objects of non-trivial topology have been intensively studied. In the course of these efforts, antiskyrmions (aSks) were recently observed in the tetragonal Heusler material Mn1.4PtSn by Lorentz Transmission Electron Microscopy (LTEM). This material is also known to host a wide range of other magnetic structures such as non-topological (NT) bubbles, elliptical skyrmions and spin helices [3]. |
Thursday, March 9, 2023 10:00AM - 10:12AM |
S55.00009: How can entangled quantum probes learn about the entanglement present in matter? ABU ASHIK MD IRFAN, Roger Pynn, Gerardo Ortiz Scattering techniques have been routinely used to study the structural and dynamic properties of matter. So far, no probe has exploited the characteristic trait of quantum mechanics, namely entanglement. We argue that when a probe is entangled in its different degrees of freedom (for example, trajectory, momentum, energy, orbital angular momentum, and spin), one can observe new phenomena not present in conventional unentangled probes. We derived a general theory for a probe that is entangled in its trajectory and spin degrees of freedom; we applied the theory to the case of entangled neutron scattering from magnetic matter. We show that when the probe is entangled, it can directly unveil the presence of entanglement in the target matter. When the latter is maximally entangled the typical Young-like interference pattern that exists otherwise for an unentangled state gets quantum erased [1]. Moreover, we show that this kind of probe can successfully differentiate between different chiral orders in magnetic materials. |
Thursday, March 9, 2023 10:12AM - 10:24AM |
S55.00010: Hall Effect Induced by Topologically Trivial Target Skyrmions Tan Dao, Sergey S Pershoguba, Jiadong Zang Electrons moving through a noncoplanar magnetic texture acquire a Berry phase, which can be described as an effective magnetic field. This effect is known as the topological Hall effect and has been observed in topological spin textures. Motivated by recent experimental realizations, here we study the Hall effect in a nontopological magnetic texture known as a target skyrmion. We start from a simplified classical picture and show that the Hall signal is a nonmonotonic function of both the electronic energy and target skyrmion radius. That observation carries over to the fully quantum mechanical treatment in a Landauer-Büttiker formalism in a mesoscopic setting. Our results suggest that it may possible to detect the presence of target skyrmions in experiments and call for further experimental investigation of the Hall effect in such textures. |
Thursday, March 9, 2023 10:24AM - 10:36AM |
S55.00011: Control of magnetism at the microscopic level with magnetic fields Sunil K Karna, Madalynn Marshall, Weiwei Xie, Lisa M DeBeer-Schmitt, David P Young, Ilya Vekhter, William A Shelton, Andras Kovács, Michalis Charilaou, John F DiTusa Information storage and manipulation technologies rely on the formation and control of nanoscopic magnetic domains. Key limitations on information density include thermal fluctuations of small magnetic domains and large thermal loads produced by currents necessary to manipulate them. In contrast, magnetic systems displaying topologically nontrivial magnetic structures have been shown to be robust against thermal fluctuations and can be manipulated with small currents. Here we use Lorentz transmission electron microscopy and small-angle neutron scattering measurements to demonstrate control over the domain topology of an anisotropic hexagonal chiral magnet Mn1/3NbS2. Magnetic solitons, twists of magnetization along a single direction, are observed to controllably form either soliton/soliton or soliton/antisoliton pairs which translate and annihilate when exposed to small magnetic fields. |
Thursday, March 9, 2023 10:36AM - 10:48AM |
S55.00012: Designing magnetic properties in CrSBr through hydrostatic pressure and ligand substitution Evan J Telford, Daniel G Chica, Kaichen Xie, Nick Manganaro, Chun-Ying Huang, Jordan Cox, Avalon H Dismukes, Xiaoyang Zhu, James P Walsh, Ting Cao, Cory R Dean, Michael E Ziebel, Xavier Roy The ability to control magnetic material properties is crucial for fundamental research and underpins many information technologies. Two-dimensional materials are a particularly exciting platform due to their high degree of tunability and ease of implementation into nanoscale devices. Here we report two approaches for manipulating the A-type antiferromagnetic properties of the layered semiconductor CrSBr through hydrostatic pressure and ligand substitution. Hydrostatic pressure compresses the unit cell, continuously decreasing the Néel temperature and increasing all saturation fields. Ligand substitution, realized synthetically through Cl alloying, decreases the Néel temperature and all saturation fields, and also decreases the magnetocrystalline anisotropy energy. A detailed structural analysis combined with first-principles calculations reveal alterations in magnetic properties are intricately related to changes in Cr-Cr distances and the Cr-halogen superexchange pathway. Our work demonstrates opportunities for pre- and post-synthetic design of magnetism in this class of ternary layered magnetic semiconductors and suggests routes for enhancing magnetic order. |
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