Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session G42: Spin Textures and Chiral Magnetism in 2D MaterialsFocus
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Sponsoring Units: GMAG DMP Chair: Hongxin Yang, Chinese Academy of Sciences Room: 709/711 |
Tuesday, March 3, 2020 11:15AM - 11:27AM |
G42.00001: Topological Magnetic-Spin Structures in Two-Dimensional Van Der Waals Cr2Ge2Te6 Myung-Geun Han, Joseph Garlow, Yu Liu, Huiqin Zhang, Donald DiMarzio, Mark Knight, Cedomir Petrovic, Deep Jariwala, Yimei Zhu Long-range ferromagnetic order down to atomic layers provides an important degree of freedom in engineering two-dimensional (2D) materials and their heterostructure devices for spintronics, valleytronics and magnetic tunnel junction switches. Using direct imaging by cryo-Lorentz transmission electron microscopy we report that topologically nontrivial magnetic-spin states, skyrmionic bubbles, can be realized in exfoliated insulating 2D van der Waals Cr2Ge2Te6. Due to the competition between dipolar interactions and uniaxial magnetic anisotropy, hexagonally-packed nanoscale bubble lattices emerge in the ab plane by field cooling. Despite a range of topological spin textures arising due to pair formation and annihilation of Bloch lines, bubble lattices with single chirality are prevalent. Our observation of topologically-nontrivial homochiral skyrmionic bubbles in exfoliated vdW materials provides a new avenue for novel quantum states in atomically-thin insulators for magneto-electronic and quantum devices. |
Tuesday, March 3, 2020 11:27AM - 11:39AM |
G42.00002: Multiple ferromagnetic transitions and structural distortion in the van der Waals ferromagnet VI3 at ambient and finite pressures Elena Gati, Yuji Inagaki, Tai Kong, Robert J. Cava, Yuji Furukawa, Sergey L. Bud'ko, Paul C Canfield Magnetic van-der-Waals (vdW) materials are considered as promising candidate systems to realize low-dimensional ferromagnetism in semiconductors. Here, we present a thermodynamic (specific heat and magnetization) and microscopic NMR study on bulk single crystals of the recently discovered ferromagnetic vdW material VI3 at ambient and finite pressures [1]. Our results show that VI3 undergoes a structural transition, which is subsequently followed by two ferromagnetic transitions at ambient pressure, giving rise to two distinct magnetically-ordered V sites for low temperatures. Upon increasing pressure, the two magnetic transitions merge at p ~ 0.6 GPa, and for even higher pressures (p ~ 1.25 GPa) merge with the structural transition. From these observations, we infer that the magnetic structure in bulk single crystals of VI3 is complex, with magnetoelastic coupling being of significant importance. |
Tuesday, March 3, 2020 11:39AM - 11:51AM |
G42.00003: First principles Calculation of Dzyaloshinskii–Moriya interaction in 2D magnetic van der Waals heterostructures Kai Huang, Ding-Fu Shao, Evgeny Y Tsymbal Magnetic skyrmions are nanoscale spin textures promising for next-generation spintronic applications. Recent studies have demonstrated that skyrmions can be generated at the interface between a ferromagnetic layer and a nonmagnetic heavy-metal-based layer due to a large Dzyaloshinskii–Moriya interaction (DMI) induced by broken inversion symmetry and strong spin-orbit coupling. This usually requires multilayer heterostructures with sizable thickness, which limit the nanoscale application. Recent discoveries of two-dimensional (2D) magnets and the related van der Waals heterostructures offer the possibility for skyrmions to emerge at the atomic scale layer thickness. Here, we predict the emergence of a large DMI in bilayer magnetic van der Waals heterostructures composed of a 2D ferromagnetic metal Fe3GeTe2 monolayer and a nonmagnetic monolayer. Based on first-principles density functional theory calculations, we find that the DMI, the exchange coupling, and the magnetic anisotropy of the magnetic van der Waals heterostructures can be modulated by the interfacial proximity effect, leading to the tunable skyrmion behaviors. Our work indicates the 2D magnetic van der Waals heterostructures are promising platforms for the skyrmion-based spintronics. |
Tuesday, March 3, 2020 11:51AM - 12:03PM |
G42.00004: Realization of very large Dzyaloshinskii-Moriya interaction and skyrmion states in two-dimensional Janus manganese dichalcogenides Jinghua Liang, weiwei wang, Haifeng Du, Mairbek Chshiev, Albert Fert, Hongxin Yang The Dzyaloshinskii-Moriya interaction (DMI), which only exists in noncentrosymmetric systems, is responsible for the formation of exotic chiral magnetic states. However, it is absent in most theoretically predicted and experimentally confirmed two-dimensional (2D) magnetic thin films so far. In this report, we perform first-principles calculations to demonstrate that significant DMI can be obtained in a series of Janus monolayers of manganese dichalcogenides MnXY (X/Y = S, Se, Te, X ≠ Y) in which the difference between X and Y on the opposites sides of Mn breaks the inversion symmetry. In particular, the DMI amplitudes of MnSeTe and MnSTe are comparable to those of state-of-the-art ferromagnet/heavy metal (FM/HM) heterostructures. Moreover, by performing Monte Carlo simulations, we find that the MnSeTe and MnSTe monolayers can host stable skyrmion states with the application of a moderate external magnetic field. The present results pave the way for new device concepts utilizing chiral magnetic structures in specially designed 2D ferromagnetic materials. |
Tuesday, March 3, 2020 12:03PM - 12:15PM |
G42.00005: Topological Spin Textures in Janus Monolayers of Chromium Trihalides Cr(I,X)3 Changsong Xu, Junsheng Feng, Yousra Nahas, Sergei Prohorenko, Hongjun Xiang, Laurent Bellaiche Topological magnetic states are promising for ultra-dense memory and logic devices. Recent progresses in two-dimensional magnets encourage the idea to realize topological states, such as skrmions and merons, in freestanding monolayers. However, monolayers such as CrI3 lack Dzyaloshinskii-Moriya interactions (DMI) and thus do not naturally exhibit skyrmions/merons but rather a ferromagnetic state. Here we propose the fabrication of Cr(I,X)3 Janus monolayers, in which the Cr atoms are covalently bonded to the underlying I ions and top-layer Br or Cl atoms. By performing first-principles calculations and Monte-Carlo simulations, we identify strong enough DMI, which leads to not only helical cycloid phases, but also to topologically nontrivial states, such as the intrinsic domain wall skyrmions in Cr(I,Br)3 and the magnetic-field-induced bimerons in Cr(I,Cl)3. Microscopic origins of such spin textures are revealed as well. |
Tuesday, March 3, 2020 12:15PM - 12:27PM |
G42.00006: Electrical excitation of superfluid- and string-like domain wall modes in layered van der Waal antiferromagnets Mohammad Mushfiqur Rahman, Avinash Rustagi, Yaroslav Tserkovnyak, Pramey Upadhyaya Efficient excitation of magnons (collective spin excitation in magnetically ordered materials) has been a limiting factor in designing low-dissipation magnonic devices. The recent emergence of low-dimensional van der Waal magnets [such as CrI3] with demonstrated electrical control of magnetic order [Nature Mat. 17, 406 (2018)] opens up new opportunities in the field of magnonics. Motivated by these developments, we theoretically demonstrate the electrical excitation of superfluid- and string-like modes harbored by the antiferromagnetically coupled domain walls of bilayer CrI3. Furthermore, we show that dc magnetic fields provide a handle for selectively exciting the mode of choice. |
Tuesday, March 3, 2020 12:27PM - 12:39PM |
G42.00007: Merons in Monolayer CrCl3 Xiaobo Lu, Ruixiang Fei, Li Yang Noncollinear spin textures in low-dimensional magnetic systems such as skyrmions, magnetic bobbles and merons have been studied for decades with their extraordinary properties derived from their chirality and topological nature. Here, using first principles and Monto Carlo simulations, we propose that monolayer chromium chloride (CrCl3) can be a promising candidate to observe paired magnetic vortex type and antivortex type topological defects, which are so-called merons. Through this paper, we demonstrate the existence of vortex and antivortex type meron pairings within the low temperature range (below 5K). Moreover, higher-order combinations of those meron pairs which are similar to the “quadrupole” excitations are also identified. Finally, including the in-plane and out-of-plane external magnetic field, we show the robustness of merons’ pairing and a rich phase space to tune the hybridizations between the ferromagnetism and meron excitations. |
Tuesday, March 3, 2020 12:39PM - 12:51PM |
G42.00008: Anomalous spin-Hall effect in 2D Cr-based materials Yuri Dahnovsky, Andrei S. Zadorozhnyi We study the THE in various systems on 2D magnetic materials (CrIS3, CrCl3, and CrBr3). From the estimations a skyrmion size is about 30-40 nm. The computations of a spin Hall effect and magnetoresistance require the calculations of the nonequilibrium distribution function, which we will determine from the kinetic Boltzmann equation. The distribution function describes by a 4 × 4 matrix because of different spin projections and the spin-dependent momenta of conducting electrons. The matrix elements contain various parameters such as effective masses, exchange constants, etc., that will be found from the first principle calculations. The reason why such system exhibit topological Hall effect is because the scattering transition probability matrix has an antisymmetric part with respect to the scattering angle. The scattering asymmetry acts as an effective magnetic field, which sign can be either the same for both spin projections of an incident electron, hence leading to a topological charge Hall effect, or opposite for different electron spin projections, leading to the topological spin Hall effect |
Tuesday, March 3, 2020 12:51PM - 1:03PM |
G42.00009: Skyrmions in TMD-based antiferromagnetic triangular lattices Aldo Raeliarijaona, Wuzhang Fang, Po-Hao Chang, Kirill Belashchenko, Alexey Kovalev We study the adsorption of magnetic transition metal atoms (Cr, Mn, Fe, and Co) on top of a TMDs such as MoS2 or WSe2, where the transition metal atoms form a triangular lattice. We conducted Monte Carlo simulations and analytical studies to obtain and characterize the magnetic ground state and determine the phase diagram for systems with AFM triangular lattice. The Heisenberg exchange parameters, single-ion anisotropy constants, and Dzyaloshinskii-Moriya vectors were extracted from first-principles density functional calculations. We found that without external magnetic field spirals are the most stable textures. Furthermore, we demonstrate the possibility of stabilizing antiferromagnetic skyrmion lattices living on 3 sublattices in such system under the influence of an external magnetic field. |
Tuesday, March 3, 2020 1:03PM - 1:39PM |
G42.00010: Chirally coupled nanomagnets Invited Speaker: Zhaochu Luo Magnetically coupled nanomagnets have many potential applications including non-volatile memories, logic gates and sensors. In order to realize functional 2-D networks of coupled nanoscale magnetic elements such as those used for nanomagnet logic [1] and artificial spin ice [2], it is desirable to engineer effective lateral magnetic couplings in a controllable way. Up to now, this has been achieved by exploiting the long-range dipolar interaction. However, the dipolar interaction is non-local and scales inversely with the magnet volume, so limiting its use in applications involving nanometer sized structures and thin films. |
Tuesday, March 3, 2020 1:39PM - 1:51PM |
G42.00011: Tuning Magnetic Order with Iron Intercalation in Transition Metal Dichalcogenides Caolan John, Spencer Doyle, Eran Maniv, James Analytis The transition metal dichalcogenides are a class of two-dimensional materials currently under intense research due to their attractive electronic properties. Through the process of intercalation, magnetic atoms can be inserted between the layers of these materials to introduce long range magnetic order, enabling exploration of magnetism in these systems. I will present magnetization and thermodynamic measurements that indicate antiferromagnetic order in iron intercalated NbS2. Crucially, we can use intercalation to control the strength of an emergent spin glass state below intercalation values of x = 1/3 in FexNbS2. The cooperation between this glassy phase and the antiferromagnetic order allow for the generation of substantial bias fields in the system. |
Tuesday, March 3, 2020 1:51PM - 2:03PM |
G42.00012: Electrical switching in a magnetically intercalated transition metal dichalcogenide Eran Maniv, Nityan Nair, Caolan John, Spencer Doyle, Joseph Orenstein, James Analytis Advances in controlling the correlated behavior of transition metal dichalcogenides have opened a new frontier of many-body physics in two dimensions. A field where these materials have yet to make a deep impact is antiferromagnetic spintronics – a relatively new research direction promising technologies with fast switching times, insensitivity to magnetic perturbations, and reduced crosstalk. Here, we present measurements on the intercalated TMD Fe1/3NbS2 which exhibits antiferromagnetic ordering below 42K. We find that remarkably low current densities of order 104 A/cm2 can reorient the magnetic order, which can be detected through changes in the sample resistance, demonstrating its use as an electronically-accessible antiferromagnetic switch. Fe1/3NbS2 is part of a larger family of magnetically intercalated TMDs, some of which may exhibit switching at room temperature, forming a platform from which to build tunable antiferromagnetic spintronic devices. |
Tuesday, March 3, 2020 2:03PM - 2:15PM |
G42.00013: Evidence for a pressure-induced gapped spin-liquid ground state in a coupled ladder antiferromagnet C9H18N2CuBr4 Tao Hong, Tao Ying, Qing Huang, Sachith Dissanayake, Yiming Qiu, Mark M Turnbull, Andrey Podlesnyak, Yan Wu, Huibo Cao, David Tennant, Kai Schmidt, Stefan Wessel Here we present a comprehensive neutron scattering study on a spin-1/2 coupled ladder antiferromagnet C9H18N2CuBr4 (DLCB for short) under applied hydrostatic pressure. In DLCB, the inter-ladder coupling is sufficiently strong to drive the system to the long-range antiferromagnetic ordering phase below TN=2 K [1]. Analysis of the spin Hamiltonian suggests that DLCB is close to the quantum critical point in two dimensions at ambient pressure and zero field [2]. Single-crystal neutron diffraction measurements under pressure suggest that the magnetic order breaks down above a ciritical pressure Pc~1.0 GPa. By contrasting with quantum Monte Carlo calculations of the dynamic structure factor, the follow-up inelastic neutron scattering study above Pc reveals evidence of a gapped spin-liquid phase with the Z2 topological order, characterized by excitation spectra of fully gapped visons and deconfined spinons. |
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