Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session A41: 2D Magnetic Materials |
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Sponsoring Units: GMAG DMP FIAP DCOMP Chair: Chi Zhang, Cornell University Room: 707 |
Monday, March 2, 2020 8:00AM - 8:12AM |
A41.00001: Discovery of Intrinsic Two-dimensional Ferromagnetism in CrTe2 Thin films Xiaoqian Zhang, Jacob Cook, Qiangsheng Lu, Guang Bian Two-dimensional (2D) layered ferromagnetic (FM) materials have attracted much interest recently since the discovery of intrinsic 2D ferromagnetism in atomically thin layers. Due to the reduced dimensionality, 2D magnets usually exhibit weak magnetic ordering compared to conventional bulk magnets. In this work, we report robust 2D ferromagnetism in chromium ditelluride (CrTe2) nanofilms whose electronic structure and magnetic properties are clearly resolved by angle-resolved photoemission spectroscopy (ARPES), superconducting quantum interference device (SQUID) and X-ray magnetic circular dichroism (XMCD). The robust ferromagnetism has been experimentally evidenced, and persists up to 250 K. In addition, the electron band structure of the ferromagnetic ground state was clearly resolved by in-situ ARPES. These experimental evidences establish CrTe2 nanofilms as an outstanding 2D vdW magnet for spintronics applications. |
Monday, March 2, 2020 8:12AM - 8:24AM |
A41.00002: Magnetic field- and temperature-dependent resonant Raman spectroscopy of bulk CrI3 Siwen Li, Zhipeng Ye, Xiangpeng Luo, Gaihua Ye, Shangjie Tian, Hechang Lei, Kai Sun, Rui He, Liuyan Zhao The van der Waals magnet CrI3 has been thought to host ferromagnetism in its bulk form and interlayer antiferromagnetism in its few-layer form. The magnetic excitations in bulk CrI3 have been probed by inelastic neutron scattering, while those in CrI3 films have been studied with inelastic magneto-tunneling spectroscopy and Raman spectroscopy. Despite such intensive effort, it remains mysterious till now how the interlayer magnetism evolves from the ferromagnetic type in bulk to the antiferromagnetic one in thin films and what the low energy magnetic excitations are in CrI3. In this talk, we will present our results on temperature- and magnetic field-dependent resonant Raman spectroscopy studies on bulk CrI3. We will show our experimental evidences on the complex spin wave structures in bulk CrI3 and their intricate magnetic field dependence. We will further discuss the magnetic field dependence of phonons and explore the interplay between the lattice and the spin degrees of freedom in bulk CrI3. |
Monday, March 2, 2020 8:24AM - 8:36AM |
A41.00003: Electric-Field Control of 2D Magnetism in Bilayer VI3 Thi Phuong Thao Nguyen, Kunihiko Yamauchi, Tamio Oguchi The recent discovery of two-dimensional van-der-Waals (vdW) magnetic materials has received much interest owing to its potentials for future spintronics device applications. There is a large number of recent publications on two-dimensional honeycomb ferromagnet CrI3, which belong to the family of transition-metal trihalides MX3 with X = Cl, B, and I, as a promising candidate materials for spintronics and magnetoelectronic applications. VI3 is a new discovered material that belongs to the transition-metal trihalides. While its structure and bulk properties have been investigated, there is a lack of information about the magnetism in the thin film. In this presentation, we will present our first-priciple study on the magnetic properties in bilayer VI3 and the influence of applied electric-fields on the magnetism. We predict that the magnetic stability of bilayer VI3 systems can be tuned by external electric fields and the effect is comparable with the case of bilayer CrI3. To understand the physics behind, the geometry, stability, and electronic and magnetic properties of bilayer VI3 will be discussed by presenting the projected density of state and the band structure. |
Monday, March 2, 2020 8:36AM - 8:48AM |
A41.00004: Light-controlled magnetism in vanadium-doped tungsten disulfide monolayers Valery Ortiz Jimenez, Yen Thi Hai Pham, Vijaysankar Kalappattil, Fu Zhang, Mauricio Terrones, Manh-Huong Phan Transition metal dichalcogenides (TMDs) have received growing attention for their outstanding electrical and optical properties. A promising way to induce long-range ferromagnetism (FM) in TMDs is by introducing magnetic dopants to form a dilute magnetic semiconductor. Our recent study shows room temperature (RT) FM in V-doped monolayer WSe2 (V-WSe2), which is an important step for TMDs based spintronics. In this work, we show light-mediated magnetism in V-WS2 at RT. We probe this effect using the magnetic LC-resonance principle which employs a soft FM Co-based microwire coil driven near resonance with an RF signal. Combined with an excellent giant magneto-impedance effect, the coil becomes highly sensitive to changes in magnetic flux through its core. The monolayer, placed at the core of the coil, is excited with a laser as we measure the change in magnetization. Interestingly, the magnetization depends on laser power and doping concentration, demonstrating the light control of 2D magnetism. We attribute this to the generation of electron-hole pairs which mediate the magnetization of the monolayer. These findings provide a promising route to exploit light-controlled FM in 2D spintronic devices. |
Monday, March 2, 2020 8:48AM - 9:00AM |
A41.00005: Strain Tuning of Magnetic Order in Two-dimensional Magnets Shengwei Jiang, Hongchao Xie, Daniel Weber, Joshua Goldberger, Jie Shan, Kin Fai Mak The recent discovery of two-dimensional (2D) van der Waals magnetic materials has received growing attention. Of particular interest are the thickness-dependent magnetic ground states in atomically thin CrI3. The competing ferromagnetic and anti-ferromagnetic interlayer exchange interactions result in a competing magnetic order that is sensitive to external perturbations including magnetic field, electrostatic gating, and hydrostatic pressure. Here we demonstrate that the magnetic order in 2D CrI3 can also be effectively tuned by applying in-plane strain. Our result demonstrates the potential for the application of 2D magnets in spin-mechanical devices. |
Monday, March 2, 2020 9:00AM - 9:12AM |
A41.00006: Tuning Magnetism of Monolayer Tungsten Disulfide by Transition Metal Doping Yen Thi Hai Pham, Valery Ortiz Jimenez, Vijaysankar S Kalappattil, Fu Zhang, Mauricio Terrones, Manh-Huong Phan The recent discoveries of intrinsic ferromagnetism (FM) in two-dimensional (2D) materials have drawn particular attention on encoding the spin behavior at low dimensions. Theoretical investigations of 2D transition metal dichalcogenides (TMDs) have predicted promising perspectives for inducing intrinsic FM in 2D TMD semiconductors by transition metal doping. This has motivated us to experimentally exploit magnetic functionality in monolayer Fe- and V-doped WS2 - a semiconducting TMD with outstanding optoelectronic and valleytronic properties. Pristine and Fe/V-doped monolayer tungsten disulfide films were grown on SiO2 substrates by a single-step solution-based method. We observe that while monolayer WS2 possesses a weak ferromagnetic ordering on its diamagnetic background, Fe:WS2 and V:WS2 monolayers exhibit strong, intrinsic FM at room temperature, which is also tunable by controlling dopant concentration. This, coupled with high-resolution TEM images, has suggested the mechanism of strong ferromagnetism in the films, resulting from the magnetic dopants and spatial-dependent ferromagnetic ordering between them. Our findings offer a prospect of developing novel 2D dilute magnetic semiconductors for future spintronic applications. |
Monday, March 2, 2020 9:12AM - 9:24AM |
A41.00007: Magnetic Correlations in the Quasi-2D Semiconducting Ferromagnet CrGeTe3 Travis Williams, Adam Aczel, Brenden Ortiz, Paul Sarte, Stephen Wilson The quasi-two-dimensional, semiconducting ferromagnets CrSiTe3 and CrGeTe3 have been studied as candidates for spintronics applications due the relatively accessible transition temperatures and large magnetic moments. While CrSiTe3 has been more studied due to the ease of growing crystals, CrGeTe3 is more interesting due to the higher transition temperature TC = 61 K. In this study, we use neutron scattering to measure the static and dynamic magnetic properties. Neutron diffraction was used to study the 3D order below TC, as well as two dimensional static correlations above the transition. Preliminary inelastic measurements shed light on the nature of the spin gap and magnetic correlations that drive the magnetism in this material, which can be contrasted to previous work on CrSiTe3. |
Monday, March 2, 2020 9:24AM - 9:36AM |
A41.00008: First-principles theory of proximity spin-orbit torque on a two-dimensional magnet: Current-driven antiferromagnet-to-ferromagnet reversible transition in bilayer CrI3 Kapildeb Dolui, Marko Petrovic, Klaus Zollner, Petr Plechac, Jaroslav Fabian, Branislav Nikolic The recently discovered two-dimensional (2D) magnetic insulator CrI3 is an intriguing case for basic research and spintronic applications since it is a ferromagnet in the bulk, but an antiferromagnet in bilayer form, with its magnetic ordering amenable to external manipulations. Using first-principles quantum transport approach, we predict that injecting unpolarized charge current parallel to the interface of bilayer-CrI3/monolayer-TaSe2 van der Waals heterostructure will induce spin-orbit torque (SOT) and thereby driven dynamics of magnetization on the first monolayer of CrI3 in direct contact with TaSe2. By combining calculated complex angular dependence of SOT with the Landau-Lifshitz-Gilbert equation for classical dynamics of magnetization, we demonstrate that current pulses can switch the direction of magnetization on the first monolayer to become parallel to that of the second monolayer, thereby converting CrI3 from antiferromagnet to ferromagnet while not requiring any external magnetic field. The transition can be detected by passing vertical read current through the vdW heterostructure, encapsulated by bilayer of hexagonal boron nitride and sandwiched between graphite electrodes, where we find tunneling magnetoresistance of 240% [1]. |
Monday, March 2, 2020 9:36AM - 9:48AM |
A41.00009: Large anomalous Nernst effect in a van der Waals ferromagnet Fe3GeTe2 Jinsong Xu, William Adam Phelan, Chia-Ling Chien Anomalous Nernst effect, a result of charge current driven by temperature gradient, provides a probe of the topological nature of materials due to its sensitivity to the Berry curvature near the Fermi level. Fe3GeTe2, one important member of the recently discovered two-dimensional van der Waals magnetic materials, offers a unique platform for anomalous Nernst effect because of its metallic and topological nature. Here, we report the observation of large anomalous Nernst effect in Fe3GeTe2. The anomalous Hall angle and anomalous Nernst angle are about 0.07 and 0.09 respectively, far larger than those in common ferromagnets. By utilizing the Mott relation, these large angles indicate a large Berry curvature near the Fermi level, consistent with the recent proposal for Fe3GeTe2 as a topological nodal line semimetal candidate. Our work provides evidence of Fe3GeTe2 as a topological ferromagnet, and demonstrates the feasibility of using two-dimensional magnetic materials and their band topology for spin caloritronics applications. |
Monday, March 2, 2020 9:48AM - 10:00AM |
A41.00010: WITHDRAWN ABSTRACT
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Monday, March 2, 2020 10:00AM - 10:12AM |
A41.00011: Ultimate tunability of ferromagnetic anisotropy in chromium mixed halides Fazel Tafti, Thomas Tartaglia, Faranak Bahrami, Joseph Tang In recent years, chromium iodide, bromide, and chloride have received attention due to exhibiting ferromagnetic ordering in 2D which is ideal for ultrathin magneto-optical devices. Also, it has been demonstrated that by alloying the halides, the magnetic easy axis can be tuned. Here, we show the ultimate case of such alloying, by presenting a new material CrClBrI where all three halides are mixed in one composition. The crystals of CrClBrI are thin and exfoliate. We present a phase diagram of all compositions of mixed halides and demonstrate how the critical temperature, Weiss constant, and magnetic anisotropy are continuously tuned across the series. |
Monday, March 2, 2020 10:12AM - 10:24AM |
A41.00012: Spin-dependent scattering in 2D van der Waals ferromagnet Fe0.29TaS2 and its heterostructure Ranran Cai, peng lv, Wenyu Xing, Yunyan Yao, Yang Ma, Huibin Zhou, Boning Li, Yangyang Chen, Shuang Jia, Igor Zutic, Xincheng Xie, Qing-Feng Sun, Wei Han The recent emergence of two-dimensional (2D) van der Waals ferromagnets has provided a new platform for exploring magnetism in the flatland and for designing 2D ferromagnet-based spintronics devices. In this talk, we will present the spin-scattering mechanisms in quasi-2D van der Waals ferromagnet. Via systematically measuring Fe0.29TaS2 devices with different thickness, it is found that the dominant AHE mechanism is found to be skew scattering in bulk single crystal, and the contribution from intrinsic mechanism emerges and become more relevant as the Fe0.29TaS2 thickness decrease. At the end, the spin-dependent scattering at the Fe0.29TaS2/superconductor interface will be discussed. |
Monday, March 2, 2020 10:24AM - 10:36AM |
A41.00013: Stacking Dependence of the Chern Number in a Ferromagnetic Topological Magnon Insulator Heterostructure Stephen Hofer, Trinanjan Datta, Dipanjan Mazumdar Recent advances in topological materials have shown that 2D magnetic insulators can be promising hosts for topologically non-trivial magnons. In this work we focus on the topological magnetic features of these materials as they might be grown in the few-layer regime. Particularly, we explore the AA and AB stacking dependencies on the Chern numbers of a layered ferromagnetic honeycomb topological magnon insulator heterostructure. Based on our bandstructure and Berry curvature calculations we show that the evolution of the Chern numbers depend non-trivially on the number of layers and the stacking arrangement, AA or AB. Additionally, we also discuss the physical consequences of sandwiching topological and non-topological ferromagnetic layers. |
Monday, March 2, 2020 10:36AM - 10:48AM |
A41.00014: Quantum critical point and ferromagnetic semiconducting behavior in p-type FeAs2 Bing-Hua Lei, Yuhao Fu, Zhenzhen Feng, David Singh Ferromagnetic semiconductors are of interest due to the unusual combination of physical properties and because if tunable they may offer opportunities for studying magnetic quantum critical points. Here, we illustrate an approach for studying suitable materials based on itinerant magnetism, different from conventional magnetic semiconductors. We show that p-type FeAs2 is an example. The complex non-parabolic band structure of this material leads to a ferromagnetic instability when doped, while at the same time allowing for a modest transport effective mass. This leads to an analogy between magnetic semiconductors and thermoelectric materials. |
Monday, March 2, 2020 10:48AM - 11:00AM |
A41.00015: Temperature Dependence of the Anomalous Hall Effect from Electron Interactions Songci Li, Alex Levchenko We consider the impact of electron-electron interactions on the temperature dependence of the anomalous Hall effect in disordered conductors. The microscopic analysis is carried out within the diagrammatic approach of the |
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