Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session L46: Magnetism and Magnetoelectrics: Molecule-Based and 2D MaterialsFocus
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Sponsoring Units: GMAG DCOMP DCMP Chair: Vivien Zapf, Los Alamos Natl Lab Room: 708 |
Wednesday, March 4, 2020 8:00AM - 8:36AM |
L46.00001: σ-Dimerization of organic radicals as mechanism for strongly hysteretic magneto-strutural phase transitions Invited Speaker: Michael Shatruk In this contribution, we present a few systems of σ-dimerizing organic radicals, which provide examples of magneto-structural phase transitions that occur with a large thermal or photochemical hysteresis window. In each case, the dimerization causes drastic structural changes that underlie a substantial energy barrier for the conversion between the diamagnetic σ-dimer phase and the paramagnetic π-radical phase. We demonstrate that in the case of dithiazolyl radicals the existence of such energy barrier allows photo-generation of paramagnetic state with remarkable thermal stability. In the case of N-oxyl radicals that exist as a rotationally disordered plastic crystalline phase at room temperature and dimerize into a long-range ordered crystalline phase upon cooling, the barrier to the intra-dimer bond breaking causes a large thermal hysteresis, which exhibits high sensitivity to applied pressure. We will also discuss general requirements for observing such transitions for other organic radicals. |
Wednesday, March 4, 2020 8:36AM - 8:48AM |
L46.00002: Controlling the Kinetics of Spin Transitions through Heterostructure Elasticity John Cain, Wanhong He, Jerry L. Zhang, Daniel R. Talham, Mark W Meisel An often overlooked feature of spin transitions is the significant volume change associated with altered metal-ligand bonding between the two spin states. Recent examples of exploiting the strain developed during a spin transition include integration into hybrid materials to influence electrical, optical, or magnetic properties. These applications all require the spin transition material to physically couple to other components; however, an interface with another material can strongly influence the behavior of the spin transition material, especially as sizes approach the nanoscale. Our lab has shown these interfaces can dramatically influence the kinetics of solid-state spin transitions. For example, the rate of the light-induced spin transition in RbxCo[Fe(CN)6]y (RbCoFe-PBA) increases by several orders of magnitude when RbCoFe-PBA is used as the core of a core-shell particle, relative to uncoated RbCoFe-PBA. A theoretical electroelastic model was used to guide chemical alterations, allowing the mechanism to be probed experimentally with nuclear inelastic scattering. |
Wednesday, March 4, 2020 8:48AM - 9:00AM |
L46.00003: Microscopic theory of spin-crossover phase transition and magnetoelectric coupling Jie-Xiang Yu, Dian-Teng Chen, Jie Gu, Jia Chen, Jun Jiang, Long Zhang, Xiaoguang Zhang, Vivien Zapf, Hai-Ping Cheng The molecular magnet Mn(taa) is one of the earliest studied spin-crossover system where the spin can transit from a low-spin state to a high-spin state around 45 K. Very recently, the magnetoelectric coupling was observed in Mn(taa) and a microscopic theory is needed. Here, we investigated the atomistic origin of the phase transition and magnetoelectric coupling in spin-crossover system Mn(taa) via first-principles calculations and Monte Carlo simulations. By constructing a molecular-scale Hamiltonian, we discovered that the Jahn-Teller-induced inter-molecular strain interaction is the key factor in both the spin-crossover phase transition and magnetoelectric behaviors. Our work leads to a first theory that goes beyond the mean field approximation. |
Wednesday, March 4, 2020 9:00AM - 9:12AM |
L46.00004: Observation of magnetoelectric, spin-lattice, and electron-phonon coupling in multiferroic (NH4)2[FeCl5(H2O)] Kendall Hughey, Jisoo Nam, Minseong Lee, Amanda Clune, Kenneth R O'Neal, Avery Blockmon, Wei Tian, Mykhaylo Ozerov, Vivien Zapf, Jun Hee Lee, Janice Lynn Musfeldt We bring together pulsed-field polarization techniques, magnetoinfrared spectroscopy, and lattice dynamics calculations to uncover the high magnetic field coupling mechanism of polarization and magnetic field in (NH4)2[FeCl5(H2O)] and to explore the structural distortions that this system undergoes through various magnetic phases and across the magnetic quantum phase transition. High-field polarization is quenched by the quasicollinear to collinear sinusoidal magnetic transition. Strikingly, spin-lattice coupling across the magnetic quantum phase transition reveals that nearly all low-frequency vibrations modulate magnetic exchange via hydrogen- and halogen-bonding interactions. An analysis of combined techniques demonstrates that magneto-infrared is sensitive to both spin-phonon and electron-phonon coupling. |
Wednesday, March 4, 2020 9:12AM - 9:24AM |
L46.00005: Magneto-optical Detection of Chirality Induced Spin Selectivity in 2D Chiral Hybrid Organic-Inorganic Perovskites Zhengjie Huang, Brian Bloom, Zheni Nikolaeva Georgieva, Eric Vetter, David Waldeck, Dali Sun The Chirality-Induced Spin Selectivity (CISS) effect, an appealing‘spin filtering’ effect arising from the chirality of materials has been demonstrated in various organic systems. The recent convergence of chiral molecules with metal halide frameworks gives rise to a new family of chiral systems: 2D chiral hybrid organic-inorganic perovskites (2D-chiral-HOIPs). This class of materials possesses both the implanted chirality and the excellent photovoltaic properties, making it a promising platform that bridges opto-spintronic studies and the CISS effect. Here we show the observation of light-induced CISS effect in the 2D-chiral-HOIPs detected by a magneto-optical measurement. It shows that the incident light changes the Kerr response of the ferromagnetic layer attached to the chiral-HOIP layer. The change of Kerr signal follows a linear relation with respect to the applied magnetic field, of which the sign of the slope depends on the chirality of the HOIPs. Our results pave a new route for employing 2D-chiral-HOIPs for future opto-spintronic applications. |
Wednesday, March 4, 2020 9:24AM - 9:36AM |
L46.00006: Theoretical design of two dimensional magnetoelectrics Shuai Dong, Ling-Fang Lin Achieving magnetoelectric two-dimensional (2D) materials should enable numerous functionalities in nanoscale devices. Until now, however, predicted 2D magnetoelectric materials are very few and with coexisting yet only loosely coupled (type-I) ferroelectricity and magnetism [1]. Based on physical analysis and by using density functional theory calculations, a type-II multiferroic MXene Hf2VC2F2 monolayer is predicted. For multiferroic MXene Hf2VC2F2 monolayer, its ferroelectricity originates directly from its magnetism [2]. The noncollinear 120o Y-type spin order generates a polarization perpendicular to the spin helical plane. Remarkably, the multiferroic transition is estimated to occur above room temperature. Our investigation should open the door to a new branch of 2D materials in the pursuit of intrinsically strong magnetoelectricity. |
Wednesday, March 4, 2020 9:36AM - 9:48AM |
L46.00007: Gate tunability of 2D antiferromagnet magnon modes Xiao-Xiao Zhang, Lizhong Li, Kin Fai Mak, Jie Shan The recently discovered atomically-thin magnetic crystals provide a unique playground to develop new approaches to manipulate magnetism. Rapid progresses have been made that demonstrate the potentials of utilizing 2D magnets to construct novel spintronics devices. However, their spin dynamics, which are crucial for microscopic understanding and determine the fundamental limit of spin manipulation, still remain elusive due to the difficulty to characterize these micron-sized samples with conventional microwave techniques. In this talk, we will show how we can access and probe the collective spin-wave excitations in an antiferromagnetic bilayer CrI3, which allows us to extract magnetic anisotropy and exchange energy. In particular, we will demonstrate the gate tunability of magnon frequencies, which is unique for the 2D magnet system. |
Wednesday, March 4, 2020 9:48AM - 10:00AM |
L46.00008: 2D ferromagnetism in porphyrin-based semiconductors Artem Pimachev, Robert D Nielsen, Anri Karanovich, Yuri Dahnovsky We study an environmentally stable 2D ferromagnetic semiconductor with applications in biomedicine, solar cells, spintronics, and energy and hydrogen storage. We describe the electronic, transport, optical, and magnetic properties of a π-conjugated micropore polymer with three iron atoms placed in the middle of an isolated pore. We study how these properties change when bonded with CO, CO2, and O2. This material exhibits strong Fe-localized dz2 bands with a direct bandgap of 0.28 eV. The material is a ferromagnet of an Ising type with long-range exchange interactions with a very high magnetic moment per unit cell, m = 6 μB. The estimated exchange integral is calculated to be about Jnn = 25 meV. The binding of CO, CO2, and O2 modifies the dz2 bands of the Fe ions with varying indirect bandgaps with values between 0.269 - 0.626 eV, 0.039 - 0.434 eV, and 0.291 - 0.347 eV for CO, CO2, and O2, respectively. Both the absorption coefficient and conductivity have large modifications to the xy-components. The material remains ferromagnetic with the magnetic moment per unit cell decreasing to 4, 2, and 0 μB for gases attached to one, two, and three Fe ions per unit cell, respectively. |
Wednesday, March 4, 2020 10:00AM - 10:12AM |
L46.00009: Low-Damping Ferromagnetic Resonance in Electron-Beam Patterned, High-Q Vanadium Tetracyanoethylene Magnon Cavities Andrew Franson, Na Zhu, Seth Kurfman, Michael Chilcote, Denis Candido, Kristen S. Buchanan, Michael Flatté, Hong X Tang, Ezekiel Johnston-Halperin Integrating patterned, low-loss magnetic materials into microwave devices and circuits presents many challenges due to the specific conditions that are required to grow ferrite materials, driving the need for flip-chip and other indirect fabrication techniques. The low-loss (α=3.98 x 10-5), room-temperature ferrimagnetic coordination compound vanadium tetracyanoethylene (V[TCNE]x) is a promising new material for these applications that is potentially compatible with semiconductor processing. Here we present the deposition, patterning, and characterization of V[TCNE]x thin films with lateral dimensions ranging from 1 micron to several millimeters. We employ electron-beam lithography and liftoff using an aluminum encapsulated PMMA/P(MMA-MAA) copolymer bilayer on sapphire. Growth occurs in an argon atmosphere at 30 mTorr and 50 °C. Films patterned via this method maintain low-loss characteristics down to 25 microns with only a factor of 2 increase down to 5 microns. A manifold of thickness and radial confined spin wave modes reveals the quality of the patterned films. This work establishes the versatility of V[TCNE]x for applications requiring highly coherent magnetic excitations ranging from microwave communication to quantum information. |
Wednesday, March 4, 2020 10:12AM - 10:24AM |
L46.00010: Two-dimensional magnetic coordination polymers: tuning the surface and the magnetic properties. Samuel Mañas-Valero, Eugenio Coronado Magnetic two-dimensional (2D) materials have emerged recently with examples of inorganic monolayers like antiferromagnets (FePS3) [Nano Letters 16, 7433, 2016; 2D Materials 3, 031009, 2016] and highly unstable ferromagnets such as CrI3 [Nature 546, 270, 2017] or Fe3GeTe2 [Nature Materials 17, 778. 2018]. |
Wednesday, March 4, 2020 10:24AM - 10:36AM |
L46.00011: A New Mercury-based Cation Radical Salt: α-(BEDT-TTF)2Hg(SeCN)2Cl Alyssa Henderson, Kaya Wei, Johan Van Tol, Rachael Richardson, Komalavalli Thirunavukkuarasu, Theo Siegrist, John A Schlueter BEDT-TTF [BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene, henceforth referred to as ET] cation radical salts continue to serve as important physical representations of various theoretical quantum systems. The arrangement of ET radical cations in these materials have dramatic effects on their physical properties. Here we report the synthesis of the new α-(ET)2Hg(SeCN)2Cl salt. Single crystals, crystallizing in the monoclinic space group P21/n, were prepared through the use of electrocrystallization.1 The two dimensional crystal structure is characterized by layers of ET radical cations separated by dimerized Hg(SeCN)2Cl- anions. The synthesis, structure, and magnetization, heat capacity, electron-spin-resonance, and Raman measurements are reported. |
Wednesday, March 4, 2020 10:36AM - 10:48AM |
L46.00012: Magneto-elastic coupling in multiferroic metal-organic framework [(CH3)2NH2]Co(HCOO)3 Komalavalli Thirunavukkuarasu, Rachael Richardson, Zhengguang Lu, Nan Huang, Dmitry Smirnov, David Mandrus Metal-organic frameworks (MOFs) are a class of nanoporous compounds where organic groups are used in combination with transition metal ions to obtain multifunctional materials. The family of MOFs comprised of methylammonum (A= (CH3)2NH2) and metal (B=Co, Cu, Fe, Mn, Ni) cations with a formate (X=HCOO3) anion are very interesting because of their multiferroic properties [1]. Therefore, several efforts have been made to understand the exchange interactions in these materials including magnetization at magnetic fields up to 60 T and infrared spectroscopy at fields up to 35 T [2,3]. Concurrently, we performed Raman spectroscopy on [(CH3)2NH2]Co(HCOO)3 at magnetic fields up to 31T to probe the magneto-elastic coupling. Also, the effect of hydrostatic pressure on the magnetic-elastic coupling in this system was explored. We will discuss our investigations and its implications. |
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L46.00013: High throughput ab initio screening for magnetic two dimensional materials Xue Jiang Quantum information and spintronics devices, based on searching and manipulating magnetism, open up new questions in the studies of two dimensional materials. In this talk, I will present our theoretical design on few new types of 2D ferromagnetic materials (MBene, CrSBr, K2N, and 2D MOFs). They are shown robust ferromagtism coupling, high Curie temperature (Tc), and large magnetic anisotropy energy (MAE). Many strategy have also been introduced to tailor their magnetic behavior, such as chemical functionalization, isoelectronic substitution, non-stoichiometry, strain, and metal decoration. |
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