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Saima A Siddiqui, Jiahao Han, Joseph T Finley, Caroline A Ross, Luqiao Liu
Owing to the difficulty in detecting and manipulating the magnetic states of antiferromagnetic materials, studying their switching dynamics using electrical methods remains a challenging task. By employing heavy-metal-rare-earth-transition-metal alloy bilayers, we experimentally study current-induced domain wall dynamics in an antiferromagnetically coupled system. We show that the current-induced domain wall mobility reaches a maximum at the angular momentum compensation point. With experiment and modeling, we further reveal the internal structures of domain walls and the underlying mechanisms for their fast motion...
August 3, 2018: Physical Review Letters
Vilmos Kocsis, Karlo Penc, Toomas Rõõm, Urmas Nagel, Jakub Vít, Judit Romhányi, Yusuke Tokunaga, Yasujiro Taguchi, Yoshinori Tokura, István Kézsmárki, Sándor Bordács
The ultimate goal of multiferroic research is the development of a new-generation nonvolatile memory devices, where magnetic bits are controlled via electric fields with low energy consumption. Here, we demonstrate the optical identification of magnetoelectric (ME) antiferromagnetic (AFM) domains in the LiCoPO_{4} exploiting the strong absorption difference between the domains. This unusual contrast, also present in zero magnetic field, is attributed to the dynamic ME effect of the spin-wave excitations, as confirmed by our microscopic model, which also captures the characteristics of the observed static ME effect...
August 3, 2018: Physical Review Letters
Yee Sin Ang, Hui Ying Yang, L K Ang
We identify a new universality in the carrier transport of two-dimensional (2D) material-based Schottky heterostructures. We show that the reversed saturation current (J) scales universally with temperature (T) as log(J/T^{β})∝-1/T, with β=3/2 for lateral Schottky heterostructures and β=1 for vertical Schottky heterostructures, over a wide range of 2D systems including nonrelativistic electron gas, Rashba spintronic systems, single- and few-layer graphene, transition metal dichalcogenides, and thin films of topological solids...
August 3, 2018: Physical Review Letters
Q Li, M Yang, Cheng Gong, R V Chopdekar, Alpha T N'Diaye, Gong Chen, J Turner, Andreas Scholl, Padraic Shafer, Elke Arenholz, Andreas K Schmid, Sheng Wang, Kai Liu, Nan Gao, A S Admasu, Sang-Wook Cheong, Chanyong Hwang, J Li, Feng Wang, Xiang Zhang, Ziqiang Qiu
Magnetic van der Waals (vdW) materials have emerged as promising candidates for spintronics applications especially after the recent discovery of intrinsic ferromagnetism in monolayer vdW materials. There has been a critical need for tunable ferromagnetic vdW materials beyond room temperature. Here we report a real space imaging study of itinerant ferromagnet Fe3GeTe2 and the enhancement of its Curie temperature well above ambient temperature. We find that the magnetic long-range order in Fe3GeTe2 is characterized by an unconventional out-of-plane stripe domain phase...
August 16, 2018: Nano Letters
Y F Peng, C M Dai, H Z Shen, X X Yi
The spin texture of the surface state for topological insulators can be manipulated by the polarization of light, which might play a potential role in the applications in spintronics. However, the study so far in this direction mainly focuses on the classical light-topological-insulators interactions; TIs coupled to quantized light remains barely explored. In this paper, we develop a formalism to deal with this issue of spin texture of the surface state for topological insulators (for example Bi2 Se3 and SmB6 ) irradiated by a quantum field, and we find that the coupling between an electron and a single-mode quantum field modulates only the arrow length that represents the spin polarization of a topological surface state...
July 23, 2018: Optics Express
Xuelei Su, Zhijie Xue, Gang Li, Ping Yu
Zigzag edges of graphene nanoribbons, which are predicted to host spin-polarized electronic states, hold great promise for future spintronic device applications. The ability to precisely engineer the zigzag edge state is of crucial importance for realizing its full potential functionalities in nanotechnology. By combining scanning tunneling microscopy and atomic force microscopy, we demonstrate the zigzag edge states have energy splitting upon fusing manganese the phthalocyanine molecule with the short armchair graphene nanoribbon termini...
August 17, 2018: Nano Letters
Mengmeng Guan, Lei Wang, Shishun Zhao, Ziyao Zhou, Guohua Dong, Wei Su, Tai Min, Jing Ma, Zhongqiang Hu, Wei Ren, Zuo-Guang Ye, Ce-Wen Nan, Ming Liu
The voltage modulation of yttrium iron garnet (YIG) is of practical and theoretical significance; due to its advantages of compactness, high-speed response, and energy efficiency, it can be used for various spintronic applications, including spin-Hall, spin-pumping, and spin-Seebeck effects. In this study, a significant ferromagnetic resonance change is achieved within the YIG/Pt bilayer heterostructures uisng ionic modulation, which is accomplished by modifying the interfacial magnetism in the deposited "capping" platinum layer...
August 14, 2018: Advanced Materials
Hua-Hua Fu, Ruqian Wu
To explore new methods for the realization of the quantum spin Hall (QSH) effect in two-dimensional (2D) materials, we have constructed a honeycomb geometry (HG) by etching rows of hexagonal holes in HgTe quantum wells (QWs). Theoretical calculations show that multiple Dirac cones can be produced by HG, regardless of whether the band inversion occurs or not. Furthermore, the topological states originating from a narrow HG region in a wide ribbon show strong localization at the physical edges of the ribbon, making them easy to manipulate and exploit...
August 14, 2018: Nanoscale
Zaiyao Fei, Bevin Huang, Paul Malinowski, Wenbo Wang, Tiancheng Song, Joshua Sanchez, Wang Yao, Di Xiao, Xiaoyang Zhu, Andrew F May, Weida Wu, David H Cobden, Jiun-Haw Chu, Xiaodong Xu
Discoveries of intrinsic two-dimensional (2D) ferromagnetism in van der Waals (vdW) crystals provide an interesting arena for studying fundamental 2D magnetism and devices that employ localized spins1-4 . However, an exfoliable vdW material that exhibits intrinsic 2D itinerant magnetism remains elusive. Here we demonstrate that Fe3 GeTe2 (FGT), an exfoliable vdW magnet, exhibits robust 2D ferromagnetism with strong perpendicular anisotropy when thinned down to a monolayer. Layer-number-dependent studies reveal a crossover from 3D to 2D Ising ferromagnetism for thicknesses less than 4 nm (five layers), accompanied by a fast drop of the Curie temperature (TC ) from 207 K to 130 K in the monolayer...
August 13, 2018: Nature Materials
Mohammad Noor-A-Alam, Minseong Lee, Hyun-Jae Lee, Keunsu Choi, Jun Hee Lee
Because of surface depolarization field, there is a critical thickness for ferroelectricity in ultrathin ferroelectric films, hindering miniaturization of high-density nonvolatile memory storage devices. A controllable Rashba effect by external electric field via switchable dipole moment could be a promising way to control and manipulate the spin degrees of freedom in spintronics. Here, based on first principles calculations, we show that non-planar Ag<sub>2</sub>Te monolayer, which has been recently predicted to be a topological insulator, possess a switchable out-of-plane electric dipole moment...
August 10, 2018: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Chenying Wang, Hongjia Zhang, Chunlei Li, Yun He, Le Zhang, Xinger Zhao, Qu Yang, Dan Xian, Qi Mao, Bin Peng, Ziyao Zhou, Wanzhao Cui, Zhongqiang Hu
In spite of recent rapid development of flexible electronics, voltage tunable spintronic structures and devices on flexible substrates have been rarely studied. Here, voltage control of magnetic anisotropy (VCMA) is demonstrated via ionic gel (IG) gating on flexible polyimide substrates with a circuit operating voltage of 1.8 V. A reversible, non-volatile VCMA switching of 114 Oe is achieved in Pt/Fe/Pt multilayer, where the spatial magnetic anisotropy distribution is determined quantitatively by electron spin resonance (ESR) technique...
August 10, 2018: ACS Applied Materials & Interfaces
Benjamin M Day, Fu-Sheng Guo, Richard A Layfield
The discovery of materials capable of storing magnetic information at the level of single molecules and even single atoms has fueled renewed interest in the slow magnetic relaxation properties of single-molecule magnets (SMMs). The lanthanide elements, especially dysprosium, continue to play a pivotal role in the development of potential nanoscale applications of SMMs, including, for example, in molecular spintronics and quantum computing. Aside from their fundamentally fascinating physics, the realization of functional materials based on SMMs requires significant scientific and technical challenges to be overcome...
August 9, 2018: Accounts of Chemical Research
Oliver Gröning, Shiyong Wang, Xuelin Yao, Carlo A Pignedoli, Gabriela Borin Barin, Colin Daniels, Andrew Cupo, Vincent Meunier, Xinliang Feng, Akimitsu Narita, Klaus Müllen, Pascal Ruffieux, Roman Fasel
Boundaries between distinct topological phases of matter support robust, yet exotic quantum states such as spin-momentum locked transport channels or Majorana fermions1-3 . The idea of using such states in spintronic devices or as qubits in quantum information technology is a strong driver of current research in condensed matter physics4-6 . The topological properties of quantum states have helped to explain the conductivity of doped trans-polyacetylene in terms of dispersionless soliton states7-9 . In their seminal paper, Su, Schrieffer and Heeger (SSH) described these exotic quantum states using a one-dimensional tight-binding model10,11 ...
August 2018: Nature
Sheng-Shi Li, Ya-Ping Wang, Shu-Jun Hu, Duo Chen, Chang-Wen Zhang, Shi-Shen Yan
One-dimensional (1D) nanowires (NWs) with robust half-metallicity are a rising star in spintronics. Herein, we theoretically investigate the magnetic and electronic properties of 3d transition-metal tribromide NWs, i.e. TMBr3 (TM = Sc, Ti, V, Cr, Co, and Cu). These systems represent repeated TMBr3 motifs with octahedral configuration, and are expected to be synthesized in a nanotube using an established method. Among these NWs, both VBr3 and CuBr3 NWs exhibit a ferromagnetic (FM) ground state, accompanied by sizable magnetocrystalline anisotropic energy, which is dominated by the superexchange coupling between the TM atoms...
August 8, 2018: Nanoscale
Sergey Dushenko, Masaya Hokazono, Kohji Nakamura, Yuichiro Ando, Teruya Shinjo, Masashi Shiraishi
Electric gating can strongly modulate a wide variety of physical properties in semiconductors and insulators, such as significant changes of conductivity in silicon, appearance of superconductivity in SrTiO3 , the paramagnet-ferromagnet transition in (In,Mn)As, and so on. The key to such modulation is charge accumulation in solids. Thus, it has been believed that such modulation is out of reach for conventional metals where the number of carriers is too large. However, success in tuning the Curie temperature of ultrathin cobalt gave hope of finally achieving such a degree of control even in metallic materials...
August 7, 2018: Nature Communications
Vasudevan Iyer, Yong P Chen, Xianfan Xu
Topological insulators are promising candidates for optically driven spintronic devices, because photoexcitation of spin polarized surface states is governed by angular momentum selection rules. We carry out femtosecond midinfrared spectroscopy on thin films of the topological insulator Bi_{2}Te_{2}Se, which has a higher surface state conductivity compared to conventionally studied Bi_{2}Se_{3} and Bi_{2}Te_{3}. Both charge and spin dynamics are probed utilizing circularly polarized light. With a sub-band-gap excitation, clear helicity-dependent dynamics is observed only in thin (<20  nm) flakes...
July 13, 2018: Physical Review Letters
Ya-Zhong Dai, Bo-Wei Dong, Yi Kao, Zi-Yuan Wang, Hio-Ieng Un, Zheng Liu, Zhi-Jun Liu, Liang Li, Fang-Bai Xie, Yang Lu, Mei-Xing Xu, Ting Lei, Yu-Jie Sun, Song Gao, Shang-Da Jiang, Jian Pei
Organic semiconductors for spin-based devices require long spin relaxation times. Understanding their spin relaxation mechanisms is critical to organic spintronic devices and applications for quantum information processing (QIP). However, reports on the spin relaxation mechanisms of organic conjugated molecules are rare and the research methods are also limited. Herein, we studied the relationships between the structures and spin relaxation mechanisms by systematically varying the structure of a conjugated radical...
August 7, 2018: Chemphyschem: a European Journal of Chemical Physics and Physical Chemistry
Muhammad Arshad Kamran
Tuning the photoluminescence (PL) and magnetic properties of one dimensional (1D) semiconductors nanostructures is an extremely important in processing light, improving speed and storage capacity for optoelectronic and spintronic applications. Here we have reported the 1D Cd1-xMnxS (x = 0 ─ 0.102) nanobelts (NBs) and invegtigated its optical and magnetic properties. These NBs were synthesized by chemical vapour deposition (CVD) method. Successful incorporation of Mn ions in an individual CdS NBs has been confirmed through several characterization tools: SEM-EDX analysis, significant higher angle and phonon modes shift were observed in the XRD and Raman spectra...
August 7, 2018: Nanotechnology
Louis Donald Notemgnou Mouafo, Florian Godel, Georgian Melinte, Samar Hajjar-Garreau, Hicham Majjad, Bruno Dlubak, Ovidiu Ersen, Bernard Doudin, Laurent Simon, Pierre Seneor, Jean-Francois Dayen
Fabrication and spintronics properties of 2D-0D heterostructures are reported. Devices based on graphene ("Gr")-aluminium nanoclusters heterostructures show robust and reproducible single-electron transport features, in addition to spin-dependent functionality when using a top magnetic electrode. The magnetic orientation of this single ferromagnetic electrode enables the modulation of the environmental charge experienced by the aluminium nanoclusters. This anisotropic magneto-Coulomb effect, originating from spin-orbit coupling within the ferromagnetic electrode, provides tunable spin valve-like magnetoresistance signatures without the requirement of spin coherent charge tunneling...
August 6, 2018: Advanced Materials
Jyotirmoy Chatterjee, Stephane Auffret, Ricardo Sousa, Paulo Coelho, Ioan-Lucian Prejbeanu, Bernard Dieny
A novel multi-functional antiferromagnetic coupling layer (MF-AFC) combining Ru and W is revealed to realize an extremely thin (3.8 nm), back-end-of-line compatible as well as magnetically and electrically stable perpendicular synthetic antiferromagnetic layer (pSAF), essential for spintronic memory and logic device applications. In addition to achieving antiferromagnetic RKKY coupling, this MF-AFC also acts as a Boron sink and texture-breaking layer. A detailed optimization of the thickness of the various involved layers has been carried out to obtain extremely thin-pSAF reference layer with stable magnetic properties, which enables the realization of sub-20 nm STT-MRAM cells...
August 6, 2018: Scientific Reports
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