Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session V39: Order and Excitations in Van Der Waals MagnetsFocus Live
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Sponsoring Units: GMAG DMP Chair: Stuart Calder, Oak Ridge National Lab |
Thursday, March 18, 2021 3:00PM - 3:12PM Live |
V39.00001: Moiré magnetism Kasra Hejazi, Zhu-Xi Luo, Leon Balents We introduce a general framework to study moiré structures of two-dimensional Van der Waals magnets using continuum field theory. The formalism eliminates quasiperiodicity and allows a full understanding of magnetic structures and their excitations. In particular, we analyze in detail twisted bilayers of Néel antiferromagnets on the honeycomb lattice. A rich phase diagram with non-collinear twisted phases is obtained, and spin waves are further calculated. Direct extensions to zig-zag antiferromagnets and ferromagnets are also presented. We anticipate the results and formalism presented to lead to a broad range of applications to both fundamental research and experiments. |
Thursday, March 18, 2021 3:12PM - 3:24PM Live |
V39.00002: Magnetism in substitutionally doped TMDs: magnetic ground states and critical temperatures Sabyasachi Tiwari, Maarten Van de Put, Bart Soree, William Vandenberghe Recent experimental advances in the field of two-dimensional (2D) magnetism have led to new avenues of realizing 2D magnets and their applications. A wide variety of 2D Transition-metal dichalcogenides (TMDs) doped with period four transition metals are expected to show magnetic order. The larger spin-orbit coupling in heavier TMDs (e.g., MoSe2) and their larger bandgaps open up the possibility to realize localized magnetic semiconductors through substitutional doping. Moreover, the magnetic order in TMDs through metal dopants is a charge driven phenomenon, which can be controlled via an external electric field, making transition-metal doped TMDs very attractive for future applications. In this work, we theoretically model the magnetic structure of TMDs (MoSe2, WSe2, MoS2, WS2, and MoTe2) substitutionally doped with all period four metals (Ti, V, Cr, Mn, Fe, Co, and Ni), using a combination of density functional theory and the Monte-Carlo algorithm. We calculate the magnetic ground state and the critical temperature for each dopant-TMD combination. We show that the magnetic stable states of the TMD fall in five distinct categories. Finally, we show that doping MoSe2 and WSe2 with vanadium (V), results in a room-temperature (>300K) ferromagnet at a doping concentration of 5-6%. |
Thursday, March 18, 2021 3:24PM - 3:36PM Live |
V39.00003: Magnetic interactions in 2D layered van der Waals semiconductors CrPS4 and MnPSe3 probed with neutron scattering Stuart Calder, Amanda Haglund, Yaohua Liu, Daniel Pajerowski, Huibo Cao, Travis Williams, Alexander Kolesnikov, Vasile Garlea, David George Mandrus Materials in which the spin and electronic interactions are confined to two-dimensional (2D) layers offer routes to enhanced quantum behavior and potential functionality in next generation devices. Consequently, there has been recent interest in a class of materials that host isolated 2D layers weakly connected by van der Waals (vdW) bonding. These 2D vdW materials show intriguing behavior in the bulk and can often be isolated down to a few or single layers. We present results using elastic and inelastic neutron scattering on powder samples that reveal detailed insights into the magnetic interactions in two systems: CrPS4 and MnPSe3. The data allow the intralayer and interlayer exchange interactions to be extracted through model spin Hamiltonians. The implications of the magnetic interactions determined on the underlying behavior is discussed. |
Thursday, March 18, 2021 3:36PM - 3:48PM Live |
V39.00004: Theoretical prediction of a two-dimensional in-plane antiferromagnetic insulator Anan Bari Sarkar, Barun Ghosh, Bahadur Singh, Somnath Bhowmick, Hsin Lin, Arun Kumar Bansil, Amit Agarwal Recent discovery of two-dimensional (2D) magnetic materials has brought magnetism to the flatland and opened up exciting opportunities for the exploration of fundamental physics as well as novel device applications. Here, we predict a thermodynamically stable 2D magnetic material, K2CoS2, which retains its in-plane bulk antiferromagnetic (AFM) order down to the monolayer and bilayer limits [1]. Magnetic moments (2.5 μB/Co) are found to form a quasi-one-dimensional antiferromagnetically ordered chain of Co atoms. The nonmagnetic electronic spectrum of the monolayer film is found to host flatbands and van Hove singularities, which play a key role in stabilizing the magnetic ground state. Based on classical Monte Carlo simulations, we estimate the Neel temperature for the AFM monolayer to be ≈ 15 K. Our study demonstrates that K2CoS2 hosts a robust AFM state which persists from the monolayer limit to the bulk material. |
Thursday, March 18, 2021 3:48PM - 4:00PM Live |
V39.00005: Layered Antiferromagnetism Induces Large Negative Magnetoresistance in the van der
Waals Semiconductor CrSBr Evan Telford, Avalon H Dismukes, Kihong Lee, Minghao Cheng, Jedrzej R Wieteska, Amymarie Bartholomew, Yu-sheng Chen, Xiaodong Xu, Abhay Narayan, Xiaoyang Zhu, Cory R Dean, Xavier Roy The recent discovery of magnetism within the family of exfoliatable van der Waals |
Thursday, March 18, 2021 4:00PM - 4:12PM Live |
V39.00006: Detecting spin-crossover transitions with two-dimensional materials. Carla Boix-Constant, Samuel Mañas-Valero, Eugenio Coronado Spin-crossover (SCO) materials are metal complexes where the spin state of the metallic center changes between high-spin (HS) and low-spin (LS) due to the presence of an external stimulus (light, pressure, temperature…), with potential applications as memory devices or in spintronic applications [1]. |
Thursday, March 18, 2021 4:12PM - 4:24PM Live |
V39.00007: Exchange-driven magnetostriction in Two-dimensional Magnets Shengwei Jiang, Hongchao Xie, Jie Shan, Kin Fai Mak Magnetostriction, the coupling between the mechanical and magnetic degrees of freedom, finds a variety of applications in magnetic actuation, transduction, and sensing. The discovery of two-dimensional layered magnetic materials presents a new platform to explore the magnetostriction effects in ultrathin solids. Here we demonstrate an exchange-driven magnetostriction effect in mechanical resonators made of two-dimensional antiferromagnetic CrI3. The mechanical resonance frequency is found to depend on the magnetic state of the material. We quantify the relative importance of the exchange and anisotropy magnetostriction by measuring the resonance frequency under a magnetic field parallel and perpendicular to the easy axis, respectively. Furthermore, we show efficient strain-tuning of the internal magnetic interactions in two-dimensional CrI3 as a result of inverse magnetostriction. Our results establish the basis for mechanical detection and control of magnetic states and magnetic phase transitions in two-dimensional layered materials. |
Thursday, March 18, 2021 4:24PM - 4:36PM Live |
V39.00008: Neutron scattering studies of the quasi-2D antiferromagnet CrCl3 John Schneeloch, Despina A Louca, Yu Tao The magnetic behavior of quasi-two-dimensional materials is a frontier of materials research, of interest both for potential applications and to better understand the behavior of 2D systems. One such material is CrCl3, which exhibits at least two magnetic transitions on cooling [1]. Below 17 K, an intermediate region with ferromagnetic (FM) behavior is reached, thought to have FM intralayer order but interlayer disorder. Below ~14 K, antiferromagnetic (AFM) interlayer ordering is observed. Applied magnetic field can drive the AFM order into an FM-like state. To elucidate structural and magnetic behavior, we performed neutron scattering experiments on CrCl3. Single crystal neutron scattering in the AFM phase revealed, in addition to AFM Bragg peaks, diffuse scattering along the out-of-plane direction. Out-of-plane magnetic field resulted in changes to AFM Bragg peak intensities that appear inconsistent with a simple coherent spin rotation picture, as well as a slower suppression of diffuse scattering than of the peak intensities. For both ground powder and a single crystal, an anomalous increase in the in-plane lattice constant was observed below ~50 K. |
Thursday, March 18, 2021 4:36PM - 4:48PM Live |
V39.00009: Complex spin dynamics in layered CrBr3 Saima Siddiqui, Joseph Sklenar, Dmitry Lebedev, Tyler Gish, Mark C Hersam, Axel F Hoffmann Layered magnetic materials give rise to unconventional spin dynamics and electrically accessible resonance frequencies even for antiferromagnets. Towards this end, we investigated the rich spin dynamics in a layered CrBr3 crystal using magnetic resonance phenomena. Compared to the other chromium trihalides (i.e., CrX3, X = Cl, I), CrBr3 possesses unique magnetic properties such as strong ferromagnetic intralayer exchange interaction and weaker interlayer ferromagnetic coupling due to competing ferromagnetic and antiferromagnetic exchange interactions at low temperature. Here, we show that magnetic excitation for the in-plane and out-of-plane directions of CrBr3 give rise to distinct magnon modes. With the out-of-plane magnetic field, only one resonance mode (Kittle mode) is observed. However, we have identified three different modes in the CrBr3 crystal when the applied field is in-plane. We explain the origin of different modes using micromagnetics including different anisotropy and intralayer and interlayer exchange energies. Our study shows that broadband microwave transmission spectroscopy can reveal the intricate spin dynamics phenomena in layered magnetic materials that originate from the interplay of intralayer and interlayer exchange energies. |
Thursday, March 18, 2021 4:48PM - 5:00PM Live |
V39.00010: Observations of layer-dependent spin waves in atomically thin Ising magnets Hongchao Xie, Zhipeng Ye, Gaihua Ye, Shangjie Tian, Hechang Lei, Kai Sun, Rui He, Liuyan Zhao Spin waves are collective magnetic excitations that are present in crystals with long-ranged magnetic orders. The recent discovery of atomically thin two-dimensional (2D) magnetic materials unlocks the possibilities of studying and controlling abundant spin-wave phenomena in the reduced dimensionality. In the large library of 2D magnets, few-layer CrI3 attracts particular interest, because it consists of antiferromagnetically (AFM) coupled ferromagnet (FM) layers with an out-of-plane easy axis. Recent experiments have reported the studies of magnetic excitations on monolayer, bilayer, and bulk CrI3 with Raman spectroscopy [1,2,3] and with time-resolved MOKE spectroscopy [4]. However, the broken translational symmetry along the out-of-plane direction in thin flakes and the lack of inversion symmetry in even but not odd layers naturally suggest a layer number dependent spin wave excitations in few-layer CrI3, whose energy dispersions and selection rules have not been explored yet. In this presentation, I will show our experimental findings of spin waves and correspondig selection rules in few-layer CrI3 using polarization-resolved magneto-Raman spectroscopy and discuss the magnetic field dependence of these spin waves and their responses across the critical magnetic fields. |
Thursday, March 18, 2021 5:00PM - 5:12PM Live |
V39.00011: Towards predictive models of transition metal intercalation - A study of non-dilute Iron diffusion in 2H-TaS2 Isabel Craig, Katherine Inzani, Sinéad Majella Griffin 2D magnets have many applications in ultralow-power electronics owing to their unparalleled optical adressibility, however relatively few stable candidates have been identified to date. Atomically thin, magnetically doped transition metal dichalcogenides are a promising new class of 2D magnets, in which magnetism originates from chemical dopants instead of the host lattice. However as synthetic routes relying on chemical intercalation have been recently proposed, the intercalation dynamics in these materials is not yet understood. We investigate iron diffusion in atomically thin 2H-TaS2 using first principles calculations. To estimate the diffusive behavior, we construct an on-lattice diffusion model to calculate the diffusion constants at a set of characteristic temperatures and intercalation densities using Kinetic Monte Carlo. We fit the interaction between octahedrally coordinated sites to a pairwise form and evaluate the diffusion barrier for itinerant cations using the nudged elastic band method. Our results suggest that the iron migration proceeds through a tetrahedrally coordinated intermediate similar to lithium diffusion in TiS2 and, notably, that the diffusion barrier depends on the spin state of the iron with potential ramifications for field-controlled intercalation. |
Thursday, March 18, 2021 5:12PM - 5:24PM Live |
V39.00012: Interlayer magnetism in Fe3−xGeTe2 Xiangru Kong, Giang Nguyen, Jinhwan Lee, Changgu Lee, Stuart Calder, Andrew May, Zheng Gai, An-Ping Li, Liangbo Liang, Tom Berlijn While most studies have concluded the interlayer ordering to be ferromagnetic, there have also been reports of interlayer antiferromagnetism in Fe3−xGeTe2. From neutron diffraction experiments, scanning tunneling microscopy (STM) and density functional theory plus U calculations we conclude that the layers of Fe3−xGeTe2 are coupled ferromagnetically. Xiangru Kong et al, PRM 4, 094403 (2020) https://doi.org/10.1103/PhysRevMaterials.4.094403 |
Thursday, March 18, 2021 5:24PM - 5:36PM Live |
V39.00013: Effective tuning of magnetic structure in Ni1-xMnxPS3 Jin Hu, Rabindra Basnet, Krishna Pandey, Gokul Acharya, Md Rafique Un Nabi, Aaron Wegner Recent breakthroughs in two-dimensional magnetism have attracted interest in exploring novel van-der Waals magnetic materials. While they exhibit exciting magnetic phenomenon in bulk form, the persistence of long-range magnetic ordering in atomically thin layers has become a promising direction to study magnetism in 2D limit. Here, we report the tunable magnetic structure in a new class of AFM van-der Waals Ni1-xMnxPS3 system. Our study reveal a systematic evolution of spin-flop transitions by varying Ni:Mn content in Ni1-xMnxPS3 single crystals, implying the re-orientation of magnetic moments of the 3d element. Such effective tunning provides a playground to engineer the 2D magnetism, offering promising candidates for new phenomena arising from 2D magnetism and future device applications. |
Thursday, March 18, 2021 5:36PM - 5:48PM Not Participating |
V39.00014: Magnetic order induced polarization anomaly of Raman scattering in 2D magnet CrI3 Yujun Zhang Previous research on the spin-phonon coupling effect mainly focuses on the renormalization of phonon frequency.Here we demonstrate that the Raman polarization selection rules of optical phonons can be greatly modified by the magnetic ordering in 2D magnet CrI3. For monolayer samples, the dominant A1g peak shows an abnormally high intensity in the cross-polarization channel at low temperatures, which is forbidden by the selection rule based on the lattice symmetry. For the bilayer, this peak is absent in the cross-polarization channel for the layered antiferromagnetic (AFM) state and reappears when it is tuned to the ferromagnetic (FM) state by an external magnetic field. |
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