Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session M53: Two-Dimensional MagnetismFocus
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Sponsoring Units: DMP Room: Mile High Ballroom 1F |
Wednesday, March 4, 2020 11:15AM - 11:51AM |
M53.00001: Strongly correlated physics and magnetic properties in low-dimensional materials of TMPS3 Invited Speaker: Je-Guen Park Je-Geun Park 1,2 |
Wednesday, March 4, 2020 11:51AM - 12:27PM |
M53.00002: Probing and controlling magnetic states in 2D layered magnetic materials Invited Speaker: Jie Shan Controlling magnetism by electrical means is a key challenge to better information technology. Electrical control of magnetic states has been explored in a variety of materials including dilute magnetic semiconductors, ferromagnetic metal thin films and multiferroics. The recently emerged two-dimensional (2D) layered magnetic materials provide unprecedented opportunities to study magnetism in the 2D limit and engineer devices for electrical control through the van der Waals heterostructures. In this talk, I will discuss our recent results on probing the spins, their fluctuations and dynamics in 2D transition metal trihalides. I will also discuss about how to tune these properties by either a pure electric field or electrostatic doping and the possible physical mechanisms for the observed effects. |
Wednesday, March 4, 2020 12:27PM - 12:39PM |
M53.00003: A van der Waals metal thiophosphate ferromagnetic semiconductor AgVP2Se6 Yuxuan Peng, XIng Cheng, Pingfan Gu, Fanggui Wang, Jie Yang, Wenyun Yang, Yu Ye, Jinbo Yang The recent realization of two-dimensional (2D) magnetism in van der Waals (vdWs) magnets holds the promise for the low-power spintronic applications. The 2D semiconducting ferromagnets, which remain rare, are special important in developing 2D magnetic devices with new functionalities. Metal thiophosphate (MTP), a multifunctional 2D material system that combines the sought-after properties of complex oxides, is a promising 2D magnet system. Here, we successfully synthesize single crystals of a novel 2D ferromagnetic semiconductor MTP AgVP2Se6 with a bandgap of 2.14 eV at room temperature. Due to the nature of vdWs bonding along the c axis, the magnetic properties of the few-layer AgVP2Se6 with different thicknesses are characterized on the exfoliated samples. The AgVP2Se6 flakes exhibit significant thickness-dependent magnetic properties, and a rectangular hysteresis loop with a large coercive field of 750 Oe at 2 K and an undiminished Curie temperature of 19 K are observed in the 6.7 nm AgVP2Se6 flake. The discovered 2D hard ferromagnet AgVP2Se6 with semiconducting behavior will provide alternative platforms for exploring 2D magnetism and potential applications in spintronic devices. |
Wednesday, March 4, 2020 12:39PM - 12:51PM |
M53.00004: Tunable defect-induced magnetism in Pt-based dichalcogenides Priyanka Manchanda, Pratibha Dev The much-sought-after magnetism in two-dimensional (2D) materials is not only important for its potential applications in spintronic and magneto-optical devices, but also due to its impact on our understanding of fundamental principles in solid state physics. In addition, 2D magnetic solids offer a unique opportunity for heterogeneous assembly with potentially new emergent phenomena. Amongst recent reports of magnetic 2D materials, magnetism was experimentally observed in PtSe2 thin films and was attributed to the naturally-occuring Pt vacancies. In this theoretical work, we show that the defect-induced magnetism in the PtSe2 thin films is highly sensitive to: (i) the PtSe2 layer-thickness (ii) defect density, (iii) the strain in the layer, and (iv) substrate choice. These different factors dramatically modify magnetic properties such as, the magnitude of the local moments, strength of coupling, and even the nature of coupling between the moments. The tunability of the magnetic properties in the Pt-based dichalcogenides can be used to design novel devices for magnetoelectric and magneto-optics applications. |
Wednesday, March 4, 2020 12:51PM - 1:03PM |
M53.00005: Atomic-Scale Visualization of Reversible Phase Transformation in 2D Ferroelectric In2Se3 Fan Zhang, Zhe Wang, Lixuan Liu, Zhongyuan Liu, Wenguang Zhu, Chenggang Tao Phase transformation in emerging two dimensional (2D) materials is crucial for understanding and controlling the interplay between structure and electronic properties. In 2D In2Se3 synthesized via CVD, we observe that In2Se3 layers with thickness ranging from single layer to ~20 layers stabilize at the β phase with a superstructure at room temperature. At around 180 K the β phase converts to a more stable β′ phase that is distinct from previously reported phases in 2D In2Se31.The kinetics of the reversible thermally driven β-to-β′ phase transformation is investigated by temperature dependent TEM and Raman spectroscopy, corroborated with the expected minimum-energy pathways obtained from our first-principles calculations. DFT calculations further reveal in-plane ferroelectricity in the β′ phase. We will also discuss domain boundaries between β′ phase domains with different orientations. The domain boundary structures are visualized by atomically resolved STM imaging and the localized boundary states are revealed by STS. |
Wednesday, March 4, 2020 1:03PM - 1:15PM |
M53.00006: Anisotropic magnetic properties of novel correlated van der-Waals materials Saicharan Aswartham, Sebastian Selter, Yuliia Shemerliuk, Anja Wolter, Bernd Buechner Layered van der Waals crystals with Weak couplings between individual layers has generated enormous interest in scientific community, because of the presence of long range magnetic order down to monolayer limit. The family of transition metal trichalcogenides (TMTC) belongs to the class of layered van der Waals materials. These TMTCs exhibits many interesting physical properties such as the metal/insulator transition, magnetism, and superconductivity under pressure. Also, when thinned down to the monolayer limit, significant changes in the physical properties have been observed. Most of these properties steam from the strong 2D character associated with the layered crystal structure. Cr2Ge2Te6 is a ferromagnetic insulator whereas Ni2P2S6 & Fe2P2S6 are aniferromagnetic insulators. In this talk, I will discuss about synthesis, physical properties and the tunability of their anisotropic magnetic properties of these novel TMTCs. |
Wednesday, March 4, 2020 1:15PM - 1:27PM |
M53.00007: Intrinsic ferromagnetism in quasi two-dimensional chromium telluride nanoplates Amanda Coughlin, Yue Yao, Zhipeng Ye, Hua Guo, Yaroslav Losovyj, Herbert Fertig, Jun Lou, Rui He, Yan Li, Shixiong Zhang The recent demonstration of ferromagnetic order in atomically thin crystals has opened many new opportunities to study two-dimensional (2D) magnetism for novel spintronic applications. Most of the 2D magnets realized so far are van der Waals materials. In this talk, we report on the chemical vapor deposition and magnetic studies of thin nanoplates of chromium telluride, a layered magnetic material with a non-van der Waals structure. Bulk magnetization and magneto-optic Kerr effect (MOKE) measurements demonstrate a ferromagnetic order below a Tc of ~ 180 K and a strong magnetic anisotropy with an easy axis along the c-axis. We will discuss how the magnetic properties are influenced by the nanoplate thickness based on MOKE measurement of individual nanoplates. We will also discuss in detail the aging effect at ambient conditions, one of the major challenges of 2D magnets with regards to practical applications. |
Wednesday, March 4, 2020 1:27PM - 1:39PM |
M53.00008: Ferromagnetism in nitrogen-doped graphene Mukul Kabir, Rohit Babar Metal-free magnetism in graphene has remained a subject of intense research, and many research groups have invested in understanding the roles of doping, structural defects and edge structure in finite-sized nano-flakes. However, a robust long-range magnetic order has remained elusive. In this context, nitrogen-doped graphene is experimentally proposed to be a promising candidate, though the corresponding exchange mechanism endures unclear and is essential to tune further and manipulate magnetism. In this talk, we will systematically discuss the local moment formation and the concurrent interaction between various defect complexes. The importance of adatom diffusion on the differential defect abundance will be elaborated. We will establish that the direct exchange mechanism between the delocalized magnetic moment originating from the π-electron at the prevalent triazine complex to be responsible for the observed ferromagnetism. We will also discuss the role of B co-doping that further improves ferromagnetism. The present results not only provide the microscopic understanding but also direct to a synthesis strategy towards robust magnetism. |
Wednesday, March 4, 2020 1:39PM - 1:51PM |
M53.00009: Unraveling the Relationship Between Layer Stacking and Magnetic Order in Nb3X8 Systems Elisabeth Bianco, Ismail El Baggari, Christopher Pasco, Berit Goodge, Tyrel McQueen, lena Kourkoutis Niobium halides of form Nb3X8 (X=Cl or Br) are cluster-based, 2D materials that exhibit an antiferromagnetic to non-magnetic transition. In Nb3Cl8, the loss of magnetic order occurs below 90 K and has been coupled to a layer re-stacking from a 2-layer (α-phase) to 6-layer (β-phase) unit cell. The transition temperature, however, depends strongly on composition with Nb3Br8 transitioning at 293 K. While tuning magnetic ordering temperature through composition is appealing, the layer re-stacking mechanism is not understood. Here, we used controlled-temperature cryogenic scanning transmission electron microscopy (cryo-STEM) to study the re-stacking in Nb3Br8 with atomic-resolution. Our results reveal a reversible transformation from the α-phase to β-phase at ~250 K upon cooling and the reverse at ~425 K upon heating through a series of intermediate phases. Tracking the emergence of intermediates with electron diffraction and Multislice image simulations provides a clearer picture of favorable stacking configurations for van der Waals Nb3X8. Understanding these stacking changes and their effect on magnetic ordering will afford handles for materials with tailored transition temperatures. |
Wednesday, March 4, 2020 1:51PM - 2:03PM |
M53.00010: High mobility in a layered antiferromagnet Shiming Lei, Jingjing Lin, Yanyu Jia, Mason Gray, Tong Gao, Andreas Topp, Fanny Rodolakis, Jessica L McChesney, Christian R Ast, Ken Burch, Sanfeng Wu, N. Phuan Ong, Leslie Schoop 2D, or ultrathin, magnetic materials are being studied as a new paradigm for device design. Intrinsic magnetic order in atomically thin layered materials has been confirmed only recently. Thus far magnetic 2D materials are mostly insulating or semiconducting; none possesses high electronic mobility. A material that exhibits simultaneously magnetic order and high mobility would enhance development of high-speed spintronic devices. In this talk, I will show how we can use chemcial rules to design a materils that can combine high mobility and magnetism and also crysaltiilizes in a strucutre with a vand der Waald gap. I will introduce the LnTe3 family as such highly conducting antiferromagnetic layered materials. In bulk GdTe3, the mobility reaches more than 60,000 cm2/Vs, [3] which is the highest mobility yet recorded for layered magnetic (ferro or antiferro) materials, and is comparable to non-magnetic, high-mobility materials such as black phosphorous. I will also show GdTe3 can be mechanically exfoliated to the monolayer limit, which will allow future investiagtion of the proeties in the 2D limit as well as open avenues for future device design. |
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