Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session R38: Monolayer Magnets IIFocus
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Sponsoring Units: GMAG DMP Chair: Scott Crooker, Los Alamos National Laboratory Room: BCEC 206B |
Thursday, March 7, 2019 8:00AM - 8:12AM |
R38.00001: First-principles Study on Ferromagnetism in Two-dimensional Fe3GeTe2 Jingzhao Zhang, Jing Wang, Yuanbo Zhang, Junyi Zhu Identifying new magnetic materials is key to better device performance and new device paradigm. Recently, the discoveries of two-dimensional (2D) ferromagnetic (FM) insulators have drawn a lot of attention to the searching of 2D magnetic materials. Here, by density functional theory calculation with different functionals as well as effective Hubbard U parameters, we symmetrically studied layered metallic magnet Fe3GeTe2 (FGT) from bulk to monolayer. Generally, LDA functional can give a correct description of the interlayer FM coupling, which is consistent with our experimental results. We simulated the ionic gate by electron doping in tri-layer FGT, explaining the mechanism of Tc dispersion as a function of doping level revealed in experiments, by applying Stoner model. Moreover, by obtaining the intralayer and interlayer exchange parameters, we found that the itinerant ferromagnetism persists in FGT down to monolayer with an out-of-plane magnetocrystalline anisotropy. Finally, the calculated Tc by mean field calculation is consistent with the experimental value. |
Thursday, March 7, 2019 8:12AM - 8:24AM |
R38.00002: Above-room-temperature Ferromagnetism in Wafer-scale Two-dimensional Fe3+xGeTe2 Films Shanshan Liu, Zihan Li, Ke Yang, Hua Wu, Faxian Xiu Recently, 2D ferromagnetic materials have been discovered with tunable magnetism and nodal-line features. Controlling 2D magnetism in exfoliated nanoflakes via electric-field enables the boosted Curie temperature (TC). One of the most intriguing challenges, however, is the realization of high Tc materials that are tunable, robust and compatible with the commercial-level manufacturability. Here, we report the above-room-temperature ferromagnetic order in wafer-scale 2D Fe3+xGeTe2 films through a non-equilibrium growth process in molecular beam epitaxy. The perpendicular magnetic anisotropy in Fe3+xGeTe2 is found to persist up to 320 K, significantly higher than the stoichiometric bulk counterpart (Fe3GeTe2, TC~220 K). By controlling the atomic ratio, we found a largely-modulated Tc that depends on carrier density. Corroborated with DFT calculations, we demonstrated that the higher atomic ratio further stabilizes the FM ground state by yielding a larger energy difference of EAFM-EFM, therefore enabling the enhanced ferromagnetic order in this system. Our results show an effective approach, i.e., the element doping, to produce a robust ferromagnetic order beyond room temperature in wafer-scale Fe3+xGeTe2 films, which may render practical applications for 2D spintronic devices. |
Thursday, March 7, 2019 8:24AM - 8:36AM |
R38.00003: Anomalous magnetotransport in Van der Waals ferromagnet Fe2GeTe3 Siqi Wang, Yang Xia, Takashi Taniguchi, Kenji Watanabe, Yuan Wang, Xiang Zhang Ferromagnetic Van der Waals (VdW) materials have recently emerged as a new member of two dimensional (2d) material family. In addition to potential application in spintronics industry, layered ferromagnets often exhibit exotic physical properties in stark contrast with traditional magnetic thin films. This family of materials retain their structural stability even down to monolayer limit. Through mechanical exfoliation, samples with different geometries are readily available, which may manifest drastically different behaviours. In this work, we report the anomalous magnetotransport in exfoliated Fe2GeTe3 nano flakes with a thickness step. The observed antisymmetric magnetoresistance and stepped anomalous Hall resistance indicate a circulation of electric current around the step with two magnetic domains at each side. Furthermore, the direction of the circulation is shown to have a dependence on the relative coercive field of two sides. Our work may pave the way for future magnetic information encoding with domain wall manipulation in ultrathin 2d materials. |
Thursday, March 7, 2019 8:36AM - 8:48AM |
R38.00004: Magnetism near room temperature in thin flakes of Fe5GeTe2 Dmitry Ovchinnikov, Andrew May, Bevin Huang, Zaiyao Fei, Qiang Zheng, Michael A McGuire, Xiaodong Xu Two-dimensional (2D) magnets are an emerging class of materials that exhibit intrinsic magnetic order in the ultrathin limit. An immediate challenge is to realize 2D magnetic order at high temperature. Indeed, molecular beam epitaxy has successfully synthesized monolayers that are magnetically ordered at room temperature. Controlled intercalation of Li ions into a few layers of Fe3GeTe2 also increases magnetic order from low temperature up to room temperature. However, obtaining an exfoliated 2D magnet with an intrinsically-high Curie/Neel temperature remains a challenge. Here we show experimental evidence of ferromagnetic ordering around temperature in thin flakes of cleavable van der Waals magnet Fe5GeTe2. Anomalous Hall effect measurements and magneto-optic Kerr effect point towards out of plane anisotropy. Furthermore, our devices exhibit high metallicity and a rich phase diagram. |
Thursday, March 7, 2019 8:48AM - 9:00AM |
R38.00005: Imaging magnetic structure in Van der Waals ferromagnets using nanoSQUID microscopy Charles Tschirhart, Marec Serlin, Jiacheng Zhu, Avi G Shragai, Yu Saito, Martin E Huber Van der Waals ferromagnets have been shown to host a variety of magnetic phenomena, including gate-and magnetic field-tunable transitions between ferromagnetic and layer antiferromagnetic states. I will present high resolution spatial maps of magnetic structure in exfoliated chromium iodide heterostructures, obtained using a scanning nanoscale SQUID on tip microscope, which provides sub-100 nm spatial resolution of magnetic domains across a wide range of magnetic fields spanning the coercive fields of these materials. |
Thursday, March 7, 2019 9:00AM - 9:12AM |
R38.00006: Prediction of a two-dimensional intrinsic ferromagnetic and half-metallic material MnSiTe3 Dechen Zhang, Azizur Rahman, Wei Qin, Ping Cui, Zengming Zhang, Zhenyu Zhang Two-dimensional (2D) transition metal trichalcogenides (TMT) have recently been extensively studied due to their intriguing electronic and magnetic properties. Here, based on first-principles calculations, we predict a new 2D TMT material MnSiTe3, which possesses both ferromagnetism and half-metallicity. The cleavage energy of the bulk MnSiTe3 is found to be very low, suggesting its monolayer counterpart can be obtained via direct mechanical exfoliation. More intriguingly, we demonstrate that both the ferromagnetism and half-metallicity are preserved when reducing the dimensions from the bulk to monolayer. For the monolayer MnSiTe3, we calculate the strengths of exchange interactions between nearest, next-nearest and next-next-nearest neighbors of Mn ions. The long-range ferromagnetic order is further confirmed by Monte Carlo simulations within the Heisenberg model, and the Curie temperature Tc is shown to be ~70K. Apart from the exchange interactions between magnetic atoms, the Ruderman-Kittel-Kasuya-Yosida interaction mediated by itinerant carriers also plays a crucial role in determining the ferromagnetic ground state. These findings provide a new 2D material for exploring applications in nano spintronics. |
Thursday, March 7, 2019 9:12AM - 9:48AM |
R38.00007: 2D Ferromagnetism in Silicene Materials Invited Speaker: Vyacheslav Storchak The appeal of ultra-compact spintronics drives intense research on magnetism in low-dimensional materials. Recent years have witnessed remarkable progress in engineering two-dimensional (2D) magnetism via defects, edges, adatoms and magnetic proximity. However, intrinsic 2D ferromagnetism remained elusive until recent discovery of magneto-optical response in Cr-based layers[1,2], stimulating the search for novel 2D magnets with tunable properties. We employ a bottom-up approach to produce layered structures of silicene (a Si counterpart of graphene) functionalized by rare-earth atoms, ranging from the bulk down to one monolayer. We track the evolution from the antiferromagnetism of the bulk to intrinsic 2D ferromagnetism of ultrathin layers of GdSi2 and EuSi2 [3]. Remarkably, the charge transport is found to be layer-dependent once silicene structures are scaled to a few-monolayers limit: it evolves from a Kondo-like trend to an insulating behavior once a gap opens up in its charge excitation spectrum. The discovery of a class of robust 2D magnets, compatible with the mature Si technology, is instrumental for engineering new spintronic devices. |
Thursday, March 7, 2019 9:48AM - 10:00AM |
R38.00008: ABSTRACT WITHDRAWN
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Thursday, March 7, 2019 10:00AM - 10:12AM |
R38.00009: Magnetic interfaces of MnSe2 monolayers Tomas Rojas, Anh T Ngo, Sergio E Ulloa Until recently, 2D magnetism was thought to occur together with defects or doping on different substrates. This situation changed drastically, as intrinsic Cr-based ferromagnetic monolayer materials were discovered, namely CrI3 and Cr2Ge2Te6. A different material, MnSe2, was predicted as stable ferromagnetic monolayer by first-principles calculations, and it has been successfully grown on several substrates [1]. |
Thursday, March 7, 2019 10:12AM - 10:24AM |
R38.00010: Emergent Transition Metal Dichalcogenide Monolayer Ferromagnetism at Terminated Edges Vijaysankar Kalappattil, Sadhu Kolekar, Manuel Bonilla, Raja Das, Tatiana M Eggers, Khang Hoang, Matthias Batzill, Manh-Huong Phan The recent discoveries of the strong room-temperature ferromagnetism in epitaxially grown transition metal diselenide XSe2 (X = V, Mn) monolayers have effectively heated up the field of two-dimensional (2D) van der Waals magnets [1,2]. However, the origin of the ferromagnetism in these nanosystems has remained an open question. In this talk, we demonstrate that chalcogenide (Se) atoms at terminated edges play a dominant role in the XSe2 monolayer magnetism, regardless of the transition metal being a non-magnetic element (X = W, Ti) or a magnetic element (X = V). The ferromagnetic Se edge is responsible for the observed large magnetic moment, which decreases as the size of XSe2 islands or the number of XSe2 layers increases. The role played by the magnetic transition metal (X = V) on the ferromagnetic ordering of monolayer XSe2 is also elucidated. Density functional theory (DFT) based calculations support the experimental findings. This understanding enables controlled nanoengineering of novel two-dimensional van der Waals magnets for next-generation spintronic devices and storage information applications. |
Thursday, March 7, 2019 10:24AM - 10:36AM |
R38.00011: Flat bands and Dirac cones in magnetic 2D metal-organic frameworks Tomohiro Soejima, Ru Chen, Christopher H. Hendon, Jeffrey B Neaton Metal-organic frameworks (MOFs) are interesting crystals for exploring new physics due to their tunable structure and chemical composition. 2D magnetic MOFs are of particular interest, and a composite kagome-honeycomb lattice was recently realized in a reported ferrimagnetic iron-semiquinone MOF [1]. Via molecular orbital and tight-binding analysis, and with density functional theory-based calculations, we study the iron-semiquinone MOF and show that its band structure contains multiple flatbands as well as multiple Dirac cones. We find that the MOF is semimetallic, with the Fermi level at a Dirac point; and the calculated magnetization is consistent with the reported experimental value. We also explore the effects of spin-orbit coupling and comment on the magnetism of related 2D MOFs; we also discuss how our tight-binding model might be generalized to other 2D MOFs of interest. |
Thursday, March 7, 2019 10:36AM - 10:48AM |
R38.00012: Tuning surface properties of 2D magnetic coordination polymers Samuel Mañas-Valero, Javier López-Cabrelles, Guillermo Mínguez-Espallargas, Eugenio Coronado Magnetism has been an elusive property in the 2D-land up to date. There are only few recent reports regarding inorganic monolayers of antiferromagnets (FePS3) [1, 2] and highly unstable ferromagnets such as CrI3 [2] or Fe3GeTe2 [3]. |
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