Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session A38: Magnetoelectric and Multiferroic Effects in Molecular SystemsFocus
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Sponsoring Units: GMAG DMP Chair: Janice Musfeldt, Univ of Tennessee, Knoxville Room: BCEC 206B |
Monday, March 4, 2019 8:00AM - 8:12AM |
A38.00001: Structure-property relations in multiferroic [CH3)2NH2]M(HCOO)3 (M=Mn,Co,Ni) Kendall Hughey, Amanda Clune, Michael O Yokosuk, Jing Li, Nandita Abhyankar, Xiaxin Ding, Naresh Dalal, Hongjun Xiang, Dmitry Smirnov, John Singleton, Janice Lynn Musfeldt We combine magnetization and infrared spectroscopy to unveil the B-T phase diagrams and vibrational properties of the [(CH3)2NH2]M(HCOO)3 (M=Mn,Co,Ni) family of multiferroics. While the magnetically-driven transition to BC in the Mn analog takes place at 15.3 T, much higher fields are required to saturate the Ni and Co materials. Analysis of the infrared spectrum of the Mn and Ni compounds across TC reveals splitting of the formate bending mode which functions as an order parameter of the ferroelectric transition. By contrast, the Co complex reveals a surprising framework rigidity where the ferroelectric state is driven solely by counterion freezing. With magnetic field, the Mn (and most likely, the Ni) materials engage the formate bending mode to facilitate the transition to the fully saturated magnetic states, whereas the Co complex adopts an alternate mechanism involving formate stretching distortions. Similar structure-property relations involving substitution of transition metal centers and control of the flexible molecular architecture are likely to exist in other molecule-based multiferroics. |
Monday, March 4, 2019 8:12AM - 8:24AM |
A38.00002: DFT Study of the Magnetic and Structural Properties of the DTN Molecular Crystal Maher Yazback, Shuanglong Liu, Neil Sullivan, Hai-Ping Cheng DTN or dichloro-tetrakis-thiourea-nickel (NiCl2 – [SC(NH2)2]4) is a molecular crystal whose soft lattice structure allows it to more easily deform, allowing stronger magneto-electric coupling (ME) manifestations, compared to typical ME materials. At low temperatures and in moderate magnetic fields DTN exhibits exotic behavior including a quantum phase transition into a Bose-Einstein condensate/XY antiferromagnetic state. Moreover, the presence of disorder introduced by Br doping experimentally shows evidence for the existence of a Bose glass state. This system poses a challenge when trying to accurately model structural and mechanical properties due to its weak intermolecular interactions. Our work attempts to understand the nature of DTN and Br-DTN using density functional theory (DFT). By including the effects of Van der Waals interactions using the DFT-D3 correction we show that we can get accurate lattice constants, bond lengths and bond angles, which allows us to further probe the mechanism responsible for the magneto-electric phenomena present in DTN. We also report our calculation of the exchange coupling constants and zero-field splitting constants responsible for the behavior of DTN at low temperatures. |
Monday, March 4, 2019 8:24AM - 8:36AM |
A38.00003: Electron-Beam Patterning of the Low-Loss (High-Q) Ferrimagnetic Coordination Compound V[TCNE]x~2 (Vanadium Tetracyanoethylene) Andrew Franson, Na Zhu, Seth Kurfman, Michael Chilcote, Ezekiel Johnston-Halperin, Hong X Tang Integrating patterned, low-loss magnetic materials into silicon-based devices and circuits presents many difficulties, from lattice matching requirements to extreme deposition conditions for traditional ferrite materials. Here we present the deposition, patterning, and characterization of the low-loss (α = 3.94 x 10-5), room-temperature ferrimagnetic coordination compound vanadium tetracyanoethylene, (V[TCNE]x~2). Patterning of V[TCNE]x~2 thin films from 100 nm to 1 µm thick is performed via electron-beam lithographic patterning using a poly(methyl methacrylate), poly(methyl methacrylate-methacrylic acid 8.5%) copolymer bilayer (PMMA/P(MMA-MAA)) on sapphire and silicon, and this process can be trivially extended to most inorganic substrates. The V[TCNE]x~2 is deposited on the patterned PMMA/P(MMA-MAA) via chemical vapor deposition (CVD) at 30 mTorr and 50°C in an argon atmosphere. V[TCNE]x~2 patterned in this method retains its low-loss characteristics down to feature sizes of 10s of µm, below which a non-conformal deposition regime leads to a non-trivial geometry. These results establish the versatility and potential of V[TCNE]x~2 to be incorporated in future silicon-based electronic devices. |
Monday, March 4, 2019 8:36AM - 9:12AM |
A38.00004: Electric field modulation of magnetic exchange in molecular helices detected by Electron Paramagnetic Resonance Invited Speaker: Roberta Sessoli The possibility to operate on magnetic materials through the application of electric rather than magnetic fields - promising faster, more compact and energy efficient circuits - continues to spur the investigation of magnetoelectric effects. Beyond symmetry requirements, large spin-orbit coupling is generally considered a necessary ingredient. On the contrary, a control of the spin-spin interaction by an electric field, not relying directly on spin-orbit coupling but rather on the overlap of the electronic clouds of interacting centers, would be quite appealing in the emerging field of quantum materials. |
Monday, March 4, 2019 9:12AM - 9:24AM |
A38.00005: Spin Filtering through Chiral Molecules on Semiconductors Tianhan Liu, Longqian Hu, Eric Lochner, Xiaolei Wang, Hailong Wang, Gang Shi, Fan Gao, Honglei Feng, Yongqing Li, Jianhua Zhao, Peng Xiong The effect of chirality-induced spin selectivity has been observed in a host of nanostructures involving chiral molecule monolayers on noble metals.1 However, there has been no report of similar experiments on semiconductor (SC) surfaces. Here, we report on a study of spin-selective electron transport across chiral polyalanine molecules in vertical junctions of (Ga,Mn)As/polyalanine/Au. The bottom electrode is an epitaxially strained (Ga,Mn)As film with perpendicular magnetic anisotropy. The junctions are formed in openings in a hardened PMMA layer on the (Ga,Mn)As defined by electron beam lithography. The native oxide on the exposed (Ga,Mn)As is removed by ion milling, followed immediately by polyalanine monolayer self-assembly in a solution. The top Cr/Au electrodes are thermally evaporated under liquid nitrogen cooling. The (Ga,Mn)As acts as a spin analyzer: Sweeping the perpendicular magnetic field at low temperatures, sharp jumps in the junction resistance are observed at the coercive fields, indicating spin filtering of electrons from the Au electrode by the polyalanine monolayer. The result implies a potential approach to realize spin injection and detection on SCs without using any magnetic material. |
Monday, March 4, 2019 9:24AM - 9:36AM |
A38.00006: The interplay of magnetism and chirality with valley excitons Shoufeng Lan, Xiaoze Liu, Siqi Wang, Hanyu Zhu, Yawen Liu, Cheng Gong, Jing Shi, Yuan Wang, Xiang Zhang Most biological molecules are chiral and exist in one of the two mirror-image enantiomers. The so-called homochirality of life is one of the most fundamental mysteries for human beings. Theory and experiments show that the magneto-chiral (MCh) effect albeit small may play a role in the molecular enantioselectivity of prehistoric life by simultaneously breaking both the parity-inversion and time-reversal symmetry. For the first time, we observe an excitonic MCh effect in artificially arranged van der Waals (vdW) crystals with an unprecedented giant MCh anisotropy more than 30 times larger than that in natural materials. Moreover, the observed excitonic MCh effect possesses a spectral splitting that is more than 50 times larger than that induced by the Zeeman effect. Such an excitonic MCh effect creates a link among magnetism, chirality, spin, and excitons, which has long been explored ever since the discovery of the natural optical activity by Arago and magnetically induced optical activity by Faraday in the early 19th century. Furthermore, the electronic nature of spins in two-dimensional vdW semiconductors makes the manipulation of enantioselectivity in magneto-chiral systems attractive for photochemical reactions, asymmetric synthesis, and chiral quantum optics. |
Monday, March 4, 2019 9:36AM - 9:48AM |
A38.00007: Multiferroic Quantum Criticality Awadhesh Narayan, Andres Cano, Alexander Balatsky, Nicola Spaldin The zero-temperature limit of a continuous phase transition is marked by a quantum critical point, which can generate exotic physics that extends to elevated temperatures. Magnetic quantum criticality is now well known, and has been widely explored [1]. Ferroelectric quantum critical behavior has also been recently established [2], motivating a flurry of research investigating its consequences. In this talk, I will present the concept of multiferroic quantum criticality -- in which both magnetic and ferroelectric quantum criticality occur in the same system -- that we have recently proposed [3]. I will describe the phenomenology of multiferroic quantum critical behavior, its emergence in complex transition metal perovskite oxides and propose candidate materials in which it should be observable. |
Monday, March 4, 2019 9:48AM - 10:00AM |
A38.00008: Magnetic field-temperature phase diagram of the molecule-based multiferroic (NH4)2FeCl5H2O Amanda Clune, Jisoo Nam, Kendall Hughey, Minseong Lee, Wei Tian, Jaime Fernandez-Baca, Randy Fishman, John Singleton, Jun Hee Lee, Janice Lynn Musfeldt The magnetization of a molecule-based multiferroic, (NH4)2FeCl5H2O and its deuterated analog, was measured using pulsed magnetic fields of up to 60 T and temperatures down to 0.6 K, to reveal the magnetic field-temperature phase diagram. Density functional theory and numerical simulations of the exchange interactions demonstrates the origin of non-collinearity and multiferrocity within the system. The phase diagram is different to other multiferroic materials with a cascade of transitions up to and including the 31 T transition to the fully polarized state. Together, this opens the door to further exploration of the high field phase using powered and pulsed magnets. |
Monday, March 4, 2019 10:00AM - 10:12AM |
A38.00009: Spin dynamics in molecular multiferroic (ND4)2[FeCl5(D2O)] Wei Tian, Huibo Cao, Gabriele Sala, Tao Hong, Randy Fishman, Jaime Fernandez-Baca (ND4)2[FeCl5(D2O)] is a molecular magnet that exhibits extraordinary coupled magnetic and ferroelectric properties. Applying modest magnetic field induces successive magnetic transitions with distinct magnetoelectric (ME) coupling and the underlying mechanism is not fully understood yet. Knowing the microscopic interactions is essential to understand the complex coupled phenomena. We performed inelastic neutron scattering experiments to measure the spin dynamics in (ND4)2[FeCl5(D2O)]. We will present here some INS data analysis results using linear spin wave theory. |
Monday, March 4, 2019 10:12AM - 10:24AM |
A38.00010: Giant Electrically Controlled Spinterface in Organic Ferroelectric Copolymer-based Multiferroic Tunnel Junctions Hoang Luong, Rugang Geng, Minh Pham, Tho Nguyen Controlling spin of electron by purely electrical means at high temperature is challenging and a long sought device in spintronics. In this APL (110, 053302, 2018), we report electrically controlled interfacial spin polarization, or the magnetoelectric effect in multiferroic tunnel junctions (MTJs) by employing organic ferroelectric copolymers, poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)), as a tunneling barrier. First, we show that the spontaneous ferroelectric polarization of the P(VDF-TrFE) films can be formed in a thin interlayer. Next, the tunneling magnetoresistance in the unpolarized TMJ quenches from 21% at 20 K to 0.7% at 296 K. Remarkably, the interfacial spin polarization of the device, dubbed spinterface, can be gradually tuned by an applied electric field. Upon the electric polarization reversal, the tunneling electroresistance reaches about 30% at 200 K and the spinterface of the device significantly changes up to 1000%. The interface between P(VDF-TrFE) and Co electrode might act as an electric-field-dependent spin filter causing the large magnetoelectric effect. The resistance of the MTJs can be controlled by either electric field or magnetic field, and therefore can potentially be used as a high density information storage element with four states. |
Monday, March 4, 2019 10:24AM - 10:36AM |
A38.00011: Tunnel magnetoresistance in oligophenyl based magnetic tunnel junctions Richard Mattana, Benoit Quinard, Sophie Delprat, Sophie Collin, Frédéric Petroff, Pierre Seneor Molecular spintronics, an emerging research field at the frontier between organic chemistry and spintronics, has opened novel and exciting opportunities in terms of functionalities for spintronics devices. Among those devices, molecular magnetic tunnel Junctions have attracted a growing interest over the years. Indeed, it was shown that spin dependent hybridization at the metal/molecule interface could lead to a radical tailoring of spintronics properties. To achieve this, self-assembled monolayers appear to be very promising candidates thanks to their impressive molecular scale crafting properties and easy-processing. Previous works were done with basic molecules such as linear alkanethiols. We now focus on more complex molecules integrating aromatic moieties to study how the modification of the tunnel barrier impacts the magnetic and electronic behaviour of the devices. We will present spin dependent tunneling transport underlining the main similarities and differences between alkanethiols and oligophenyls MTJs. |
Monday, March 4, 2019 10:36AM - 10:48AM |
A38.00012: Spin transport through graphene/molecules-based magnetic tunnel junctions Clement Barraud, Jacko Rastikian, Pascal Martin, Philippe Lafarge, Maria Luisa Della Rocca, Richard Mattana, Pierre Seneor, Frédéric Petroff, Bruno Dlubak Spin transport through organic molecules is motivated by the ability to tune at the atomic scale the spin injection/detection properties. This property is barely achievable in inorganic systems and it is due to the possibility of designing molecules atoms by atoms. With this respsct, ferromagnetic metal/molecules interfaces has focused most of the attention. |
Monday, March 4, 2019 10:48AM - 11:00AM |
A38.00013: Electronic Phase Separation induced dramatic enhancement of large magnetoresistance in Organic Spin Valves Wenting Yang, Qian Shi, Tian Miao, Qiang Li, Peng Cai, Hao Liu, Hanxuan Lin, Bai Yu, Yinyan Zhu, Yang Yu, Lina Deng, Wenbin Wang, Lifeng Yin, Dali Sun, Xiaoguang Zhang, Jian Shen Organic spin valves (OSVs) have been studied widely with respect to the long spin relaxation time of the carriers in the organic materials and their synthetic versatility, ease of manufacturing and pliability. Recent advances focused on the spinterface and the multi-functionalities of OSVs. Here we employ LPCMO with high spin polarization and electronic phase separation (EPS) to tune the MR of the OSV, which depends strongly on the pre-set magnetic field, voltage and temperature due to the spin-flip scattering in LPCMO and the interface. An extremely high MR of 438% and the rangeability of 5.9 times are observed. Our findings point an alternative way for multistate of OSVs and controllable room temperature OSVs by using LPCMO with high Tc and electronic phase separation. |
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