Query: Magnetic structures and magnetic device properties of edge-modified armchair-edged graphene nanoribbons

Candidate papers:

abstract: Abstract The magnetic properties based on the armchair edged graphene nanoribbons (AGNRs) are less studied in currently existing works. Here, the edge modification of AGNR by the transition metal Mn (AGNR Mn) and further functionalized with monohydrogenation (AGNR Mn H) and dihydrogenation (AGNR Mn H2) are considered. Our calculations from first principles method show that they posses three triplet antiferromagnetic (AFM) states, which are all semiconductoring for AGNR Mn and metallic for AGNR Mn H2, but semiconductoring or metallic for AGNR Mn H. Interestingly, at ferromagnetic (FM) state AGNR Mn H and AGNR Mn H2 are a half metal with bandgaps 0.46 and 0.97 eV, respectively. AGNR Mn H2 featuring both the stable magnetic ordering and the highest energy stability are predicted, as well as the calculated Gibbs free energy unveils that these three structures can stably exist in a different chemical potential range in experiment. Also shown is that the perfect spin polarization in a very large bias region and a spin valve effect with a large magnetoresistance can be achieved in a magnetic device based on AGNR Mn H2.
author_names: Z B Zhu

D J Wang

Zhenhua Zhang

Ming Qiu
title: Magnetic structures and magnetic device properties of edge modified armchair edged graphene nanoribbons
year: 2016

abstract: The electronic and magnetic structures of graphene nanoribbons (GNRs) with various edge structures passivated by P atoms are investigated systematically, and compared with H passivation as well. GNRs with the entire reconstructed Klein edge or armchair edge are found to be nonmagnetic regardless of P or H passivation. However, if the edge of GNRs is a mixture of zigzag edge and reconstructed Klein edge, they are nonmagnetic for H passivation but significantly magnetic for P passivation, which could be attributed to the "charge transfer doping" effect. And the corresponding magnetic device shows a noticeable negative differential resistance phenomenon and an excellent spin filtering effect under AP configuration, which originate from the special energy band structure. The GNRs with zigzag edge, reconstructed Klein edge, or mixed edge shapes are all metals in the nonmagnetic state regardless of the H or P atoms involved. The relationship between the energy gap and the width in armchair edged GNRs by P passivation with a dimer structure also satisfies the 3p periodicity, but different in detail from the case of H passivation. The calculated edge formation energy indicates that P passivated GNRs are energetically more favorable, suggesting that they can stably exist in the experiment.
author_names: Z L Yu

D J Wang

Z B Zhu

Z H Zhang
title: Magneto electronic properties of graphene nanoribbons with various edge structures passivated by phosphorus and hydrogen atoms.
venue: Physical chemistry chemical physics PCCP
year: 2015

abstract: Abstract The edge state, which is a peculiar magnetic state in zigzag edged graphene nanoribbons (GNRs) originating from an electron electron correlation in an edge localized p state, has promising applications for magnetic and spintronics devices and has attracted much attention of physicists, chemists, and engineers. For deeper understanding the edge state, precise fabrication of edge structures in GNRs has been highly demanded. We focus on [a.b]periacene, which are polycyclic aromatic hydrocarbons (PAHs) that have zigzag and armchair edges on molecular periphery, as a model compound for the understanding and actually prepare and characterize them. This review summarizes our recent studies on the origin of the edge state by investigating [a.b]periacene in terms of the relationship between the molecular structure and spin localizing character.
author_names: Akihito Konishi

Yasukazu Hirao

Hiroyuki Kurata

Takashi Kubo
title: Investigating the edge state of graphene nanoribbons by a chemical approach: Synthesis and magnetic properties of zigzag edged nanographene molecules
year: 2013

abstract: Abstract The structure dependent electronic properties of suspended graphene nanoribbon (GNR) have still been important issues. However, these properties have been rarely investigated experimentally due to technical difficulties to produce high quality suspended GNRs and the identification of atomic structures. Here, we report the electronic properties of suspended GNRs by in situ transmission electron microscopy observations to simultaneously obtain the structural information while measuring the current voltage (I V) curves. The suspended GNRs could be obtained by convergent electron beam nanosculpting after careful cleaning by current annealing. The I V curves were measured for GNRs with a mixture of both zigzag and armchair edges (MGNR) with widths of 3.7 to 1.9 nm and also zigzag edge GNRs (ZGNR) with widths of 1.7 to 1.2 nm. The I V curves for the ZGNRs were different from those of the MGNRs, as follows. (1) The ZGNRs showed a sharp increase at the threshold voltage in differential conductance voltage curves. (2) The band gaps measured for ZGNRs were smaller than the band gaps calculated using the GW approximation. (3) The threshold voltage increased with the GNR length. These findings support magnetic insulator and nonmagnetic metal nonequilibrium phase transitions as theoretically predicted. Narrow and short ZGNR represents the potential for further nanosized switching devices.
author_names: Chunmeng Liu

Jiaqi Zhang

Manoharan Muruganathan

Hiroshi Mizuta

Yoshifumi Oshima

Xiaobin Zhang
title: Origin of nonlinear current voltage curves for suspended zigzag edge graphene nanoribbons
year: 2020

abstract: Recent outbreaks in bottom up chemical techniques have demonstrated the synthesis of atomically perfect zigzag graphene nanoribbons (ZGNRs) and of their corresponding analogs with phenyl edge functionalization [P. Ruffieux et al. Nature 531, 489 (2016) Since spin polarized currents can be generated at the edges of the ZGNRs, the control of phenyl decoration at the zigzag edges could accurately tune the electronic properties of these carbon based nanoribbons. In the present paper, using first principles calculations and a Landauer Buttiker approach, the electronic and magnetic properties as well as the spin resolved transmissions are investigated in various phenyl edge modified ZGNRs. The understanding of the spin dependent transport properties in relation to the atomic structure opens the way to design devices such as spin valves for future spintronics applications.
author_names: Leandro Salemi

Aurelien Lherbier

Jean-Christophe Charlier
title: Spin dependent properties in zigzag graphene nanoribbons with phenyl edge defects
year: 2018

abstract: Graphene nanoribbons, quasi one dimensional structures of carbon, are fascinating materials. These structures can be constructed as strips of graphene sheet, the two dimentional honeycomb lattice of carbon with sp2 hybridization. Geometrically two main types of slice can be cut from a graphene sheet, with zigzag edge and armchair edge (Niimi05; Kobayashi05) The edge geometry is the key parameter which determines the electronic properties of the nanoribbons. Although the two dimensional graphene is a zero band gap semi metal, electronic structure of nanoribbons depend on their edge geomtery (Saito92; Klein94; Fujita96; Son06a) A simple tight binding model with one orbital per atom predicts that zigzag nanoribbons are metallic. But density functional calculations shows that all graphene nanoribbons are semiconductors at their ground state with band gaps which depend on their width and edge geometry, closing at infinite width, i. e. infinite graphene. Moreover, the electronic structure of graphene nanoribbons can be modified by chemical functionalization, such as functionalization by various atomic sepcies or by functional groups (Maruyama04a; Gunlycke07; Hod07; Gorjizadeh08) A large variety of electronic and magnetic properties, such as semiconducting with a wide range of band gap, metallic, ferromagnetic, antiferromagnetic, half metallic, half semiconducting, can be obtained by chamical modifications of the nanoribbons. Modification of the edge or using an adsorbate or substitution of carbons of the nanoribbon with an appropriate host are different options of functionalizations of these materials. These properties, along with the ballistic electronic transport, and the quantum Hall effect (Novoselov05a; Zhang05) and high carrier mobility (Novoselov05a) cause these quasi 1D materials to be promising candidates for nanoelectronics applications (Novoselov04b; Son06b; Obradovic06; Li08; Hod09; Zhu10) Various junctions can be constructed by connecting nanoribbons of different widths and types with perfect atomic interface, and electronic device can be integrated on them by selective chemical funtionalization on a single nanoribbon sheet (Huang07; Yan07; Gorjizadeh08) In order to achieve their potential for these applications it is essential to have a better understanding of the electronic structure of graphene nanoribbons and have ability to control them. From a practical point of view, when nanoribbons are fabricated
author_names: Narjes Gorjizadeh

Yoshiyuki Kawazoe

Amir A Farajian
title: Electronic and Transport Properties of Defected Graphene Nanoribbons
year: 2011

abstract: We theoretically investigate the spin dependent transport for the system of an armchair edge graphene nanoribbon (AGNR) between two ferromagnetic (FM) leads with arbitrary polarization directions at low temperatures, where a magnetic insulator is deposited on the AGNR to induce an exchange splitting between spin up and down carriers. By using the standard nonequilibrium Green's function (NGF) technique, it is demonstrated that the spin resolved transport property for the system depends sensitively on both the width of AGNR and the polarization strength of FM leads. The tunneling magnetoresistance (TMR) around zero bias voltage possesses a pronounced plateau structure for a system with semiconducting 7 AGNR or metallic 8 AGNR in the absence of exchange splitting, but this plateau structure for the 8 AGNR system is remarkably broader than that for the 7 AGNR one. Interestingly, an increase of the exchange splitting D suppresses the amplitude of the structure for the 7 AGNR system. However, the TMR is much enhanced for the 8 AGNR system under a bias amplitude comparable to the splitting strength. Further, the current induced spin transfer torque (STT) for the 7 AGNR system is systematically larger than that for the 8 AGNR one. The findings here suggest the design of GNR based spintronic devices by using a metallic AGNR, but it is more favorable to fabricate a current controlled magnetic memory element by using a semiconducting AGNR.
author_names: Benhu Zhou

Xiongwen Chen

Benliang Zhou

Kai Ding

Guanghui Zhou
title: Spin dependent transport for armchair edge graphene nanoribbons between ferromagnetic leads.
venue: Journal of physics. Condensed matter an Institute of Physics journal
year: 2011

abstract: Utilizing first principle calculations, we perform a systematic study on the electronic and magnetic properties of recently proposed graphene like Be3C2 nanostructures. We found that although the Be3C2 nanosheet exhibits a Dirac feature in the nonmagnetic state, an intrinsic antiferromagnetism is preferred and it opens a sizeable band gap of 2.75 eV at the Dirac point. The edge stabilities of Be3C2 nanoribbons (Be3C2NRs) are revealed in detail, and indicate that the armchair and zigzag edges with Be and C terminations are all possibly obtained by careful control of the H and Be chemical potentials. Akin to the Be3C2 nanosheet, these Be3C2NRs are also antiferromagnetic semiconductors regardless of the edge shapes and terminations, whose band gaps are all insensitive to the ribbon width. Peculiar spintronic behaviors can be induced in the zigzag Be3C2NRs by electric fields, which can transform the Be terminated nanoribbons into half metals and turn the C terminated ones into bipolar semiconductors or even spin gapless semiconductors. Similar electronic structures are also present in Be3Si2 and Be3Ge2 nanostructures, which are antiferromagnetic semiconductors with smaller band gaps. The valence and conduction band edges of Be3C2NRs straddle the redox potentials of water, and are suitable for photocatalytic water splitting, while for the Be3Si2 and Be3Ge2 nanostructures, the band edges could form a type II band alignment with the MoS2 nanosheet, for which the combined hetero nanostructures possess a high power conversion efficiency of up to 14 17% for photovoltaic solar cells. Our study demonstrates that beryllium group IV nanostructures exhibit versatile electronic and magnetic properties, which endow them with many potential applications in nano electrics and nano energy devices.
author_names: Yi Ding

Yanli Wang
title: Intrinsic Magnetism and Electronic Structure of Graphene like Be3C2 Nanoribbons and Their Si, Ge Analogues: A Computational Study
year: 2017

abstract: We analyze theoretically electronic, magnetic, and thermoelectric properties of narrow carbon polymers. Such nanoribbons, which can be obtained chemically via bottom up approach from the appropriate monomers, may exhibit extremely interesting properties from application point of view if modified with substitution Al/N atoms or functionalized with NOCH3 group. Our investigations, based on ab initio calculations, show that such modification may considerably narrow the bandgap with respect to pristine structures. Also, magnetic moments ordered ferromagnetically can be generated along modified edges, which results in the spin dependent band structure giving rise to remarkable spin effects, giving strongly enhanced spin Seebeck coefficient. These results suggest that modified polymeric graphene nanoribbons would have a great potential for applications in spintronic devices.
author_names: Krzysztof Zberecki

R Swirkowicz
title: Thermoelectric phenomena in chemically synthesized graphene nanoribbons with substitution atoms and functional groups
year: 2016

abstract: Effects of magnetic antidots on the transport properties of zigzag edged graphene nanoribbons ZGNRs are investigated by spin polarized first principles calculations combined with a nonequilibrium Green's function technique. Specifically, the effects of antidots or holes with regular shapes rectangular and triangular are studied. It is found that rectangular holes with a zero total spin S0 and triangular holes with a finite spin S0 cause different effects on the equilibrium conductance of ZGNRs. A rectangular hole with zigzag edges parallel to the ribbon edges blocks the transmission of the band edges of both the valence band and the conduction band from both the spin up channel and the spin down channel. Thus a much wider transmission gap than the pristine ZGNRs can be observed. However, a triangular hole with zigzag edges blocks transmission from only one spin channel in either the valence band edge or the conduction band edge. Thus the gap width in the total conductance is not affected in this case. The difference originates from the different energy shift of the valence band and conduction band relative to Fermi energy as a result of two effects: finite size effect and spin splitting from the antidot induced effective internal magnetic field. Graphene nanostructures are supposed to be very important building blocks in future nanoelectronic devices due to their remarkable structural and electronic properties. Among them, graphene nanoribbons GNRs have attracted intensive attention 1 12 and it is found that the properties of GNRs are highly dependent on their sizes and edge shapes. Tightbinding calculations show that armchair edged GNRs AGNRs can be either metallic or semiconducting depending on their widths 8,12 while first principles calculations show that AGNRs are always semiconducting with an energy gap scaling inversely to the GNR width. 8 10 More interestingly, in the zigzag edged GNRs ZGNRs, magnetic ordering is formed due to the unpaired and edge electrons. Two most stable spin configurations have been observed: ferromagnetic FM and antiferromagnetic AF, 13 which mean that the localized edge states on the two sides are FM coupled or AF coupled. Tight binding calculations show that the ZGNRs are always metallic 12 while first principles calculations show that it is metallic only in the FM configuration. There is always an energy gap in the AF configuration. Calculations also show that the most stable configuration is the AF state with the states of different spins in the valence bands and conduction bands localized on different edges while the energy of the states with different spins is degenerate. 5,8 Meanwhile, quantum dots and antidots made by graphene are another kind of graphene nanostructures which initiate great interests. 14 20 The dots are just graphene molecules with finite size in all directions while antidots are holes in graphene with some kinds of dots cut away from it. Just like in ZGNRs, magnetism can also be formed in graphene molecules with zigzag edges. 15 In a graphene molecule with rectangular or hexagonal edges, magnetic moments with the same magnitude and different signs are always formed on the two opposite zigzag edges. Thus the total spin S0 in such systems is exactly zero. However, in a molecule with triangular zigzag edges, exactly the same magnetic moments are observed on all edges. So the total spin S0 is nonzero. Like in ZGNRs, the local magnetism in graphene molecules arises from the spin polarized edge states localized on the zigzag edges. The local magnetism in graphene nanostructures may qualify graphene nanoribbons and molecules with zigzag edges as promising candidates for application in the spintronic devices. Therefore, the study of spin polarized transport through these nanostructures are quite interesting. In this work, we build graphene based devices by combining graphene nanoribbons and antidots with zigzag edges and investigate the electron transport in them. Specifically, we study the effects of graphene antidots or holes on the transport properties of ZGNRs. Two kinds of antidots will be considered: rectangular hole and triangular hole. The model structure is constructed as follows: the scatter
author_names: Xiaohong Zheng

Guoren Zhang

Zhi Zeng

Victor M Garcia-Suarez

Colin J Lambert
title: Effects of antidots on the transport properties of graphene nanoribbons
year: 2009