Spintronics and MRAM in ATK
The search for new non-volatile memory technologies is a very intensive research area today. A promising candidate is magnetic RAM (MRAM). Several academic groups and electronics companies are using ATK for different stages in the analysis of new materials for MRAM structures. ATK is a very popular tool within the entire general area of spintronics, for studies of various novel applications and devices where the information is carried not by the electron charge, but by its spin.
The Atomistix ToolKit (ATK-2014) includes the latest innovation in simulations of spintronics devices using Density Functional Theory (DFT), including non-collinear calculations with spin-orbit interactions, MetaGGA functionals, NonEquilibrium Greens Functions (NEGF) device simulations. ATK-2014 has improved the self-consistent loop for non-collinear systems, making the software very fast and robust.
Keep your focus and reach results fasterThe graphical user interface Virtual NanoLab (VNL) allows researchers to focus on the relevant points for their projects, namely the investigation of the electrical and spin properties of novel device structures, rather than spending time struggling with data import/export to visualize the results. |
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The unique feature of ATK to calculate ballistic tunneling current in nanostructures enables users to:
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Use with any material or systemATK is a very convenient tool for studies of basic properties of spin-dependent transport phenomena in a variety of systems, such as
Moreover, a local basis set expansion of the electron density is used, and ATK is therefore a more efficient tool for modeling local defects such as impurities or vacancies than plane wave codes. The algorithms used in ATK are also optimized to allow for simulations of large-scale systems, with up to 500-1,000 atoms. |
Examples and references
Below we illustrate some of the spintronics applications that users of Atomistix ToolKit have studied with the software. To view all references to papers studied with ATK, see the publication list.
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Noncollinear transport in Co2FeAl/MgO/Co2FeAl
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Zhaoqiang Bai, Lei Shen, Yongqing Cai, Qingyun Wu1, Minggang Zeng, Guchang Han & Yuan Ping Feng, New J. Phys. 16 (2014) 103033 ATK is used for non-collinear transport calculations for the spin-dependent transport characteristics of the Co2FeAl/MgO/ Co2FeAl perpendicular magnetic tunnel junctions (p-MTJs). The calculations show that the structure has exceptionally high Tunneling Magneto Resistance (TMR) of 100.000 %, and comparison with collinear simulations shows the importance of using the noncollinear formalism for the study. Further calculations reveals good thermal stability of the structure. The paper also finds a strong magneto-electric coupling which may be used to assist spin-transfer torque controlled switching of the device. The comprehensive atomic-scale modelling data in the paper, shows the material system is promising as a building block for the next-generation spin-based non-volatile memories. |
| Spin-polarized transport in a CrAs/AlAs heterojunction
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Y. Min et al., Journal of Magnetism and Magnetic Materials 321, 312 (2009) Calculations of spin-dependent quantum transport in a CrAs(001)/AlAs(001) heterogeneous junction predicts a strong diode effect of charge and spin current. The minority spin current is inhibited when a bias voltage is applied to the terminals of both CrAs and AlAs. The majority spin current is inhibited when the bias voltage is applied to the terminal of CrAs and relaxed when the bias voltage is applied to the terminal of AlAs. A charge and spin current diode is interesting for reprogrammable logic applications in the field of spintronics. |
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(CpFeCpV)n multidecker wires
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Jian-Chun Wu et al., J. Phys. Chem. C 113, 7913 (2009) Spin transport through (CpFeCpV)n multidecker wire sandwiched between magnetic Ni electrodes is simulated in the linear response regime. The amplitude and the sign of the spin filter efficiency can be manipulated by choosing the contact condition (e.g., anchoring groups, absorbing positions on Ni electrodes surface). The performance of the spin filter can be further manipulated by adjusting the length of the molecule wire. Various ways to realize nearly perfect spin-filter are illustrated. |
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Spin-polarized transport in graphene nanoribbons with impurities
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Investigation of the electronic transport properties and fundamental mechanism of spin polarization as a function of the location of impurities from the center to an edge of a graphene nanoribbon device with zigzag edges. The difference between center-located and edge-located impurities is discussed. For center-located impurities, the ferromagnetic ground state induces new spin states near the Fermi level which are responsible for the spin-polarized current. |
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Spin-polarized transport in graphene flakes
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H. Sahin & R.T. Senger, Physical Review B 78, 205423 (2008)
Study of structural, electronic, and transport properties of hydrogen-terminated short graphene nanoribbons (graphene flakes) and their functionalization with vanadium atoms. A spin-polarized current can be produced by exploiting the spatially separated edge states using asymmetric nonmagnetic contacts. Functionalization of the graphene flake with magnetic adatoms such as vanadium also leads to spin-polarized currents even with symmetric contacts. |
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Ni point contact
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Ab initio calculations on an atomic wire model demonstrate that the magnetic point contact is comprised of an abrupt change in magnetic moments at the contact region, drastically modifying only the flow of a spin-down current. The calculations reproduce nonlinear features observed experimentally, and the results therefore offer a method to analyze the spin transport in a magnetic point contact without a magnetic-field application, which can minimize the ambiguity in the origin of ballistic magnetoresistance. |
| Iron-cyclopentadienyl sandwich molecular wires
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A study on a series of novel organometallic sandwich molecular wires (SMWs), constructed with alternating iron atoms and cyclopentadienyl (Cp) rings. The wires are found to be stable and flexible, having half-metallic properties with 100% spin polarization near the Fermi level. Some wires show a nearly perfect spin filter effect when coupled between ferromagnetic electrodes. Moreover, their I-V curves exhibit negative differential resistance (NDR). The SMWs are the first half-magnetic linear molecules with showing a high spin filter effect and NDR and can be easily synthesized, suggesting that the SMWs are promising materials for application in molecular electronics. |
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TMR studies of Fe/MgO/Fe
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M. Stilling, K. Stokbro & K. Flensberg, J. Comp.-Aid. Mater. Design 14, 141 (2007) and Mol. Sim. 33, 557 (2007) Two studies of Fe/MgO/Fe MTJ structures. Among other things the influence of random perturbations to the atomic coordinates perpendicular to the Fe/MgO interface is found to lead to significant differences in the conductance. The authors also show how the conductance is lowered substantially if the Fe interfaces are oxidized (as also noticed in experiments), and discuss how inclusion of Au in the interface might reduce this problem. |
In addition, there are several spin-applications in carbon and B-N nanotubes.
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Additional case stories
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CNT-Fe-CNT junctionN. Inoue and S. Usui, Cybernet Systems, presented at the Japanese Physical Society meeting in March 2009 Spin-filter effect in a junction between two capped (5,5) carbon nanotubes, coupled with a Fe atom. Computations of transmission and PDOS is shown, and the basic mechanisms of the spin-dependent transmission are analyzed. In addition, the influence of an applied gate voltage is presented. |
