Conference Programme

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S-04: 2D Materials
Tuesday, 20/Jun/2017:
1:30pm - 3:30pm

Session Chair: Vijay Kumar, Dr. Vijay Kumar Foundation & Shiv Nadar University
Location: Rm 326

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1:30pm - 2:00pm

Computational Design of 2D Magnetic Ordering

Yunhao LU, Fang WANG, Zhaohui REN, He TIAN

Zhejiang University, China

Owning to the emergence of graphene, 2D materials become more and more important for device applications. The occurrence and control of magnetic ordering in 2D system is desired for application. Here, on the basis of 1st principle calculation, we demonstrate that the type of magnetic coupling can be changed reversibly between ferromagnetic and antiferromagnetic configuration in 2D MoN2 monolayer. And we also discuss the tunable magnetic ordering at interface of ferroelectric perovskite oxides. We provide a physical picture for understanding these striking effects. The discovery is not only of great scientific interest in exploring unusual phase transitions in low-dimensional systems, but it also reveals the great potential of the 2D material in the nanoscale mechanical, electronic, and spintronic applications.

2:00pm - 2:30pm

Electronic, Magnetic and Chemical Properties of 2D Metal Nitrides and Phosphides


University of Macau, Macau S.A.R. (China)

Two-dimensional (2D) MXenes have attracted increasing attention because of their unusual physical and chemical properties. In the talk, we will present a DFT-study on the physical and chemical properties of 2D MXenes, focusing on metal nitrides and phosphides. First, we investigate the formation possibilities of 2D metal phosphides by exploring their phonon dispersion and thermodynamic stability, and find that 2D metal phosphides can be achieved. We show that all of the phosphides are metallic and magnetic. We further show that some of them are active in hydrogen evolution reaction (HER). Secondly, we calculate the electronic and magnetic properties of 2D metal nitrides and investigate their application in Li-battery. We find that Ti2N shows the best performance in Li storage due to negligible diffusion barrier and high power density. Finally, we report that MXenes can be promising electrocatalysts in HER, especially W2C due to near-zero over-potential in a wide range of hydrogen coverage. The MXenes may apply to sensor, spintronics, and water electrolysis for hydrogen production.

2:30pm - 2:45pm

Computational Exploration of Novel 2D Materials for Dirac Half Metal and Magnetic Storage

Jijun ZHAO

Dalian University of Technology, China

In spintronics, it is highly desirable to find new materials holding complete spin-polarization, high-speed conduction electrons, large Curie temperature and robust ferromagnetic ground state simultaneously. Using first-principles calculations, we demonstrate that the stable YN2 monolayer is a novel p-state Dirac half metal (DHM), which has not only fully spin-polarized Dirac state, but also the highest Fermi velocity (3.74×105 m/s) in the DHMs reported to date [1]. In addition, its half metallic gap of 1.53 eV is large enough to prevent spin flip transition. Because of the strong nonlocal N-p direct exchange interaction, the Curie temperature reaches over 332 K. Moreover, its ferromagnetic ground state can be well preserved under carrier doping or external strain. Therefore, the YN2 monolayer is a promising DHM for high-speed spintronic devices and would lead to new opportunities of designing other p-state DHMs. Using first-principles calculations, we also explore 2D organic materials for magnetic storage devices with large magnetic anisotropy. Magnetic properties of 5d transition metal decorated 2D ployphthalocyanine framework (TM@Pc) have systematically investigated by means of DFT calculations with inclusion of spin-orbit coupling [2]. Giant perpendicular magnetic anisotropy is found in W@Pc and Re@Pc. After decorating with a homonuclear transition metal atom, an overturn of easy axis is demonstrated and the magnetic anisotropy energy can be enlarged to over 30 meV for Os and Ir.


[1] Z. F. Liu, J. Y. Liu, J. J. Zhao, Nano Research (2017), DOI: 10.1007/s12274-016-1384-3.

[2] P. Wang, X. Jiang, J. Hu, X. Huang, J. Zhao, J. Mater. Chem. C 4, 2147 (2016).

2:45pm - 3:00pm

Large Out-of-plane Spin Polarization in WTe2 Weyl Semimetal

Shuyuan SHI, Yi WANG, Qisheng WANG, Jongmin LEE, Hyunsoo YANG

National University of Singapore, Singapore

WTe2, a kind of two-dimensional Weyl semimetal with strong spin orbit coupling [1-3] and metallic-like transport behavior [4], has been receiving enormous attention from scientists in spintronics discipline [2,3]. An interface asymmetry induced out-of-plane spin orbit torque (SOT) has been reported in WTe2 very recently [3]. However, the quantification of the SOT strengths and their temperature dependence have not yet been studied.

In this work, we study both in-plane and out-of-plane SOT strengths in the WTe2 (t nm) /permalloy (Py, 6 nm) bilayer structures by the spin torque ferromagnetic resonance (ST-FMR) technique [5] at different temperatures. The WTe2 films are exfoliated from WTe2 single crystal and the WTe2/Py ST-FMR devices are fabricated by electron beam lithography and ion milling. We find that the in-plane SOT strength (θip) has a small value, which shows a very weak temperature dependence in our measurement temperature range. However, a large out-of-plane SOT strength (θop) of ~0.15 is observed at room temperature. Moreover, the θop increases as temperature decreases from 300 to 75 K, reaching the maximum at ~0.2. Further analysis indicates that the large out-of-plane SOT strength in WTe2 is essentially from damping-like torque induced by the out-of-plane spin currents generated by WTe2 layer. Our results reveal the temperature dependent SOT strengths in Weyl semimetal WTe2, which is of great importance for the development of Weyl semimetal-based spintronic devices.


[1] Ali. M. N. et al., Nature 514, 205–208 (2014).

[2] Jiang. J. et al., Phys. Rev. Lett. 115, 166601 (2015).

[3] D. MacNeill et al., Nat. Phys. (2016).

[4] C.-H. Lee et al., Sci. Rep. 5, 10013 (2015).

[5] Y. Wang et al., Phys. Rev. Lett. 114, 257202 (2015).

3:00pm - 3:15pm

Magnetic Properties of Transition-Metal Adsorbed Phosphorus Nanosheets with Octagon-Tetragon Structure: A Computational Study

Zengyao WANG1, Qingyun WU2, Lei SHEN1

1Engineering Science Programme, National University of Singapore, Singapore; 2Department of Materials Science and Engineering, National University of Singapore, Singapore

A stable allotrope of two dimensional phosphorus that is composed of octagons and tetragons (P84) has been proposed in 2016, providing researchers a good opportunity for exploring various electronic properties of it. In this study, the P84 nano sheets adsorbed with 3d transition-metal (TM) atoms (Sc-Zn) are studied using the density function theory (DFT). DFT calculations show that all TM atoms except closed shell Zn atom are able to bond strongly onto the P84 nano sheet with sizable binding energies. P84 nano sheets adsorbed with TM atoms from Sc to Co exhibit magnetic properties which arise from the exchange splitting of the TM 3d orbitals. P84 nano-sheet adsorbed with V and Cr atoms at two types of adsorption sites are studied using Monte Carlo Method in an attempt to investigate the influence of doping concentration on Curie temperature of the system. Finally, a P84 based sensor and its working mechanism is proposed.

3:15pm - 3:30pm

Carrier Density and Strain Tunable Magnetism in 2D Transition Metal Chalcogenides

Bheema Lingam CHITTARI1,2, Youngju PARK2, Dongkyu LEE2, Moonsup HAN2, Allan H. MACDONALD3, Euyheon HWANG1, Jeil JUNG2

1Sungkyunkwan University, South Korea; 2University of Seoul, South Korea; 3The University of Texas at Austin, United States

Magnetic order in two dimensional (2D) materials are attractive because they can offer unprecedented electrical and mechanical control of magnetic configurations through gate tunable carrier density and strains. In this presentation I will provide a theoretical survey on the electronic and magnetic properties of 2D chalcogenides including MAX3, MX2 and a few other structures. We will focus most of our attention on the electronic structure and magnetic properties of 2D MPX3 (M = transition metal, and X = S, Se, Te) transition metal chalcogenophosphates to examine their potential role as single-layer van der Waals materials that possess magnetic order. Our ab initio calculations predict that most of these single-layer materials are antiferromagnetic semiconductors, whose band gaps decrease as the atomic number of the chalcogen atom increases (from S to Se to Te), leading in some cases to half-metallic ferromagnetic states or to non-magnetic metallic states. We find that the phase transition boundary from antiferromagnetic semiconductor to ferromagnetic half-metal can be substantially influenced by gating or by strain engineering. The sensitive interdependence we find between magnetic, structural, and electronic properties establishes the potential of this 2D materials class for applications in spintronics, suggesting pathways for controlling the magnetic configurations and their critical temperatures by tuning system parameters such as the carrier density and strains.

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