Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session P47: Magnetism of 2D Semiconductors, Dichalcogenides and Graphene |
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Sponsoring Units: GMAG Chair: Scott Crooker, Los Alamos Natl Lab Room: 710/712 |
Wednesday, March 4, 2020 2:30PM - 2:42PM |
P47.00001: Magnetic interactions in the 2D layered van der Waals semiconductor CrPS4 Stuart Calder, Amanda Haglund, Yaohua Liu, Daniel Pajerowski, Huibo Cao, Travis Williams, Vasile O Garlea, David Mandrus Compounds with two-dimensional layers weakly connected by van der Waals bonding offer routes to enhanced quantum behavior in the bulk as well as in reduced layer materials achieved through exfoliation analogous to graphene. The presence of magnetic ions in the layers can provide new fundamental insights and possible functionality. Consequently the search and investigation of such "beyond graphene" materials has proved a recent focus for research efforts. CrPS4 is such a semiconducting magnetic van der Waals material, however has undergone only limited experimental investigations to date. Here we present a series of neutron scattering measurements that allow the magnetic structure to be determined and exchange interactions extracted. The results reveal the subtle role of competing interactions, which manifest in a non-trivial magnetic transition and a tunable magnetic structure with small applied fields. Our results in the bulk compound provide intriguiing insights that can be applied to an understanding of the behavior of reduced layer CrPS4. |
Wednesday, March 4, 2020 2:42PM - 2:54PM |
P47.00002: High Curie temperature and strain-induced spin reorientation transition in two dimensional CrPbTe3 Imran Khan, Jisang Hong We investigated the strain-induced magnetic properties of two-dimensional CrPbTe3 (CPT) monolayer belonged to the members of Cr based two-dimensional family. We explored the possibility of fabrication of 2D layer through the mechanical stability, dynamical stability, formation energy, cohesive energy, and thermal stability calculations. We found ferromagnetic ground state and the pristine CrPbTe3 monolayer had an indirect band gap of 0.25 eV with an in-plane magnetic anisotropy of -1.37 meV/cell. The Curie temperature was 110 K and this is much larger than that of CrI3, CrSiTe3, and CrGeTe3. Under the 4 % tensile strain, the band gap was increased to 0.45 eV and also the Curie temperature was enhanced to 150 K. We found strain-induced semiconductor-metal transition under the compressive strain and also the spin reorientation transition from in-plane to perpendicular magnetic anisotropy at 4 % compressive strain and the perpendicular magnetic anisotropy energy was almost three times larger than that of the CrGeTe3 layer. Our finding may suggest that the CrPbTe3 system can be utilized for spintronics and straintronic applications. |
Wednesday, March 4, 2020 2:54PM - 3:06PM |
P47.00003: Magnetic Properties of Proton Irradiated van der Waals Magnets Srinivasa Rao Singamaneni, Luis M Martinez, Hector Iturriaga, Olmos Rubyann, Qiang Wang, Shao Lin, Yu Liu, Cedomir Petrovic The advent of two-dimensional (2D) van der Waals (vdWs) magnetic crystals such as ABTe3 (A = Fe, Cr, Mn; and B = Si, Ge) creates new possibilities in exploring their magnetic properties as they are easily exfoliable. They retain their magnetic nature, chemical stability and structural integrity down to monolayers and, are readily tuned by various kinds of external stimuli, and opened enormous opportunities in controlling their magnetic states through coupling with external perturbations. Irradiation with protons has been shown to be an effective versatile method in inducing and manipulating the magnetic and electronic properties. In this work, we present and discuss the magnetic properties of proton irradiated vdWs magnets such MnSiTe3 and CrSiTe3 as a function of proton fluence (10^15 to 10^18/cm^2). Our findings show that it is possible to tune the saturation magnetization by about 53% in both these crystals. As evidenced from complementary measurements, spin-lattice coupling is strongly modified upon proton irradiation and that could cause the observed changes in the magnetic properties. |
Wednesday, March 4, 2020 3:06PM - 3:18PM |
P47.00004: Optical Characterizations of Magnetic Phases in Two-Dimensional Ferromagnetic Semiconductor CrSBr Kihong Lee, Avalon Dismukes, Evan Telford, Cory Dean, Xiaoyang Zhu, Xavier Roy
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Wednesday, March 4, 2020 3:18PM - 3:30PM |
P47.00005: Magnetic anisotropy of two-dimensional ferromagnetic insulator MnBi2Te4 Yang Li, Wenhui Duan MnBi2Te4 has attracted great interest recently due to its magnetic and topological properties. Based on the density functional theory calculation, we systematically study the magnetic anisotropy of the monolayer MnBi2Te4, which is vital for establishing the long-range magnetic order in two-dimensional system. We find the exchange interaction in monolayer MnBi2Te4 almost has no contribution to the magnetic anisotropy, as a result of the weak p-d hybridization between Mn and Te. The magnetic anisotropy originates from the single-ion anisotropy, leading to a ferromagnetic Curie temperature of about 20 K. Interestingly, the emergence of the single-ion anisotropy cannot be induced solely by the spin-orbit coupling of Mn atoms, but also involves the spin-orbit coupling of ligand Te. This behavior is very different from that in monolayer CrI3 and CrGeTe3. Our findings may provide a comprehensive understanding of the magnetic behavior in monolayer MnBi2Te4 and motivate further research on its potential applications. |
Wednesday, March 4, 2020 3:30PM - 3:42PM |
P47.00006: Ferrimagnetic excitations in the layered hexagonal compound Mn3Si2Te6 Matthew Stone, Gabriele Sala, Jiao Lin, Andrew May The layered ferrimagnet Mn3Si2Te6 orders below Tc=78 K. The S=5/2 Mn sites are arranged in alternating honeycomb and triangular lattice layers. Each honeycomb layer is ferromagnetically ordered with the moments pointing in a singular direction in the ab-plane. The triangular lattice layer has the moments also pointing in the ab-plane but in the opposite direction. A net moment is generated due to an imbalance in the Mn content within the different layer types. We examine single crystal inelastic neutron scattering measurements of the excitations in Mn3Si2Te6 below Tc. We use super-resolution image correlation techniques to refine the resolution convolved spin-wave spectrum in order to determine the exchange interactions in this system. We find significant exchange interactions orthogonal to the ab-plane, produce a network of geometrically frustrated interactions. The potential for Dirac nodes in the dispersion of the coupled ferromagnetic hexagonal layers will also be considered. |
Wednesday, March 4, 2020 3:42PM - 3:54PM |
P47.00007: Large scale synthesis of monolayer ferromagnetic Fe3GeTe2 Ryan Roemer, Chong Liu, Ke Zou Until now, the two-dimensional ferromagnets remain limited to exfoliated micron-sized samples. Large-scale thin films are desirable for the fabrication of integrated devices for spintronic and memory storage applications. We show, by molecular beam epitaxy, the synthesis of high-quality Fe3GeTe2 (FGT) films, a promising candidate that carries ferromagnetic states at room temperature upon ionic liquid gating. The FGT unit cell consists of two weakly coupled quintuple layer substructures with hexagonal symmetry, confirmed by surface x-ray diffraction. |
Wednesday, March 4, 2020 3:54PM - 4:06PM |
P47.00008: Magnetism tunability in wafer-scale few-layered van der Waals ferromagnetic Fe3GeTe2 films Shanshan Liu, ke yang, Zihan Li, Wenqing Liu, Enze Zhang, hua wu, Faxian Xiu Two-dimensional (2D) ferromagnetic materials have been discovered with tunable magnetism and nodal-line properties. 2D magnetism modulation in exfoliated nanoflakes via electrostatic gating introduces the boosted TC. One of the most intriguing challenges, however, is still the realization of high TC materials that are tunable, robust. Here, we report the effective manipulation of magnetic properties of wafer-scale 2D ferromagnetic Fe3GeTe2 films by changing the sample composition and utilizing the proximity effect in ferromagnetic/antiferromagnetic heterostructures. With the film thickness decreasing, TC drops continuously from 220 K (bulk-like) down to 130 K (few-layer). By varying the sample compositions, TC will monotonously increase as the ratio changing. TC behaves a rising trend as the ferromagnetic/antiferromagnetic heterostructure period increases. Our experiments have confirmed the room-temperature TC and the phase transition, which are consistent with the DFT calculations. The large-scale high-TC film growth and controllable ferromagnetism of Fe3GeTe2 promise the practical spintronic applications. It also opens unprecedented opportunities to explore rich physics in heterostructures of van der Waals ferromagnets with 2D superconductors and topological materials. |
Wednesday, March 4, 2020 4:06PM - 4:18PM |
P47.00009: Magnetic interactions in two-dimensional single-layer transition-metal dichalcogenides Tatsuya Shishidou, Michael Weinert The transition-metal dichalcogenides (TMD), a class of two-dimensional layered van der Waals materials, have attracted extensive interest because of the wide variety of physical properties that they exhibit. An important recent addition is the intrinsic ferromagnetic order found in atomic single layers of VSe2 [1] and MnSe2 [2] that persists above room temperature. This discovery opens up exciting opportunities [3] to study strong spin fluctuations in reduced dimensionality, as well as to engineer novel spintronic devices. In this talk, using a density-functional spin-spiral approach [4], we address the magnetic interactions in two-dimensional TMD films in the ultrathin limit. |
Wednesday, March 4, 2020 4:18PM - 4:30PM |
P47.00010: High Curie temperature in magnetically doped tungsten diselenide Sabyasachi Tiwari, Maarten L Van de Put, Bart Soree, William G Vandenberghe Two-dimensional (2D) magnets have attracted immense attention recently because of their possible use in future energy-efficient spintronic devices. A class of 2D magnetic materials are transition-metal dichalcogenides (TMDs) that are substitutionally doped with magnetic transition metals like Cr, Fe, and Mn. Especially, TMDs based on heavy elements like tungsten (W) and selenium (Se). In this work, we investigate magnetism in magnetically doped WSe2 monolayers using Density Functional Theory (DFT). In particular, we simulate the magnetic phase transition using Monte-Carlo simulations of a classical Heisenberg Hamiltonian, built for randomly doped samples of WSe2. Specifically, we investigate the effect of dopant-atom clustering on the magnetic properties of doped monolayer WSe2. To take into account the effect of the clustering of the dopant atoms, we introduce a functional form for the exchange interaction and obtain the parameters of our classical Heisenberg Hamiltonian from total energy DFT calculations. From the Monte-Carlo calculations, we extract the doping-density-dependent Curie temperature for each dopant atom. Finally, we show a high Curie temperature of about 300 K in Fe/Mn-doped WSe2 at a doping concentration of 7-8%. |
Wednesday, March 4, 2020 4:30PM - 4:42PM |
P47.00011: Magnetic Response of Graphene Flakes Sean Deyo, Selman P Hershfield The orbital diamagnetism and spin paramagnetism of graphene flakes is computed as a function of size, shape, boundary type, and temperature, using a nearest--neighbor tight binding Hamiltonian. In general the orbital magnetization per atom grows as the size of the flake increases, but not necessarily monotonically. Flakes with "open" boundaries, where open means there are atoms on the edges of the flake with only one nearest neighbor, exhibit a smaller magnetization than flakes with "closed" boundaries, where closed means every atom has at least two nearest neighbors. The orbital susceptibility increases with temperature for open flakes, whereas the closed flakes show little change at low temperatures. |
Wednesday, March 4, 2020 4:42PM - 4:54PM |
P47.00012: Computational challenges in the characterization of magnetism for atomically precise nanographenes on noble metal substrates. Carlo Antonio Pignedoli, Kristjan Eimre, Shantanu Mishra, Doreen Beyer, Oliver Gröning, Pascal Ruffieux, Roman Fasel On-surface synthesis techniques have demonstrated high flexibility and atomic precision in the fabrication of carbon-based nanomaterials, with recent examples ranging from graphene nanoribbons hosting topological quantum phases1 to specifically shaped nanographenes (NGs).2-5 NGs may exhibit a magnetic, open-shell structure as a result of their peculiar topology, which makes them highly attractive for applications in molecular electronics. Furthermore, unpaired spins in open-shell NGs may be used to perform spin logic operations. |
Wednesday, March 4, 2020 4:54PM - 5:06PM |
P47.00013: Increased Curie temperature and enhanced perpendicular magneto anisotropy of Cr2Ge2Te6/NiO heterostructure Andres Llacsahuanga Allcca, Hiroshi Idzuchi, Xing-Cheng Pan, Katsumi Tanigaki, Yong Chen Van der Waals (vdW) materials with ferromagnetic properties down to few layers such as CrI3 and Cr2Ge2Te6 have recently attracted a lot of attention due to their potential in spintronic applications. However, the Curie temperature (TC) of these vdW has remained relatively low. Here, we report increased TC and enhanced perpendicular magnetic anisotropy in Cr2Ge2Te6 (CGT) flakes interfaced with antiferromagnetic insulator NiO for a wide range of CGT thicknesses (5-200 nm). |
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P47.00014: 2D Layered Ferromagnet: the Emergence of Skyrmions in Transition Metal Dichalcogenides Yunbo Ou, Norbert Marcel Nemes, Jose Luiz Martinez, Mirko Rocci, HANG CHI, Daniel Larson, Austin Akey, Wenbo Ge, Dhavala Suri, David Charles Bell, Weida Wu, Efthimios Kaxiras, Jagadeesh Moodera Recently there is great attraction drawn towards Van der Waals (vdW) ferromagnet since the discovery of ferromagnetism in monolayer CrI3. Due to the extraordinary topology driven properties, magnetic transition metal dichalcogenides (TMDCs) appear to behave more exotically. In this work, utilizing molecular beam epitaxy, a stable CrTe2, one of TMDCs, films are fabricated down to monolayer (ML) level. Ferromagnetism is exhibited even down to the 2D insulating limit - 1 ML film. Surprisingly, the topological Hall effect (THE), which manifests the real space topology of magnetic structure in TMDCs, is observed in thicker films (> 6 ML) up to 130 K, a first such observation. Electric transport data and magnetometry data indicate a high possibility of presence of magnetic Skyrmions, real space nanometer-sized quasi-particles with topological spin textures. Although they are found in many systems even at room temperature, but not in TMDCs, until now. The discovery of magnetism in monolayer CrTe2 and topological magnetic structure in thicker CrTe2 not only enriches the 2D magnet family and the capability of TMDCs, but also pave a way for all vdW materials based spintronic devices. |
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