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26 results on '"Bapna, Mukund"'

1. Bipolar electric field switching of perpendicular magnetic tunnel junctions through voltage controlled exchange coupling

Author

Zhang, Delin, Bapna, Mukund, Jiang, Wei, de Sousa, Duarte Pereira, Liao, Yu-Ching, Zhao, Zhengyang, Lv, Yang, Sahu, Protyush, Lyu, Deyuan, Naeemi, Azad, Low, Tony, Majetich, Sara A, and Wang, Jian-Ping

Subjects
Physics - Applied Physics, Condensed Matter - Materials Science
Abstract

Perpendicular magnetic tunnel junctions (p-MTJs) switched utilizing bipolar electric fields have extensive applications in energy-efficient memory and logic devices. Voltage-controlled magnetic anisotropy linearly lowers the energy barrier of ferromagnetic layer via electric field effect and efficiently switches p-MTJs only with a unipolar behavior. Here we demonstrate a bipolar electric field effect switching of 100-nm p-MTJs with a synthetic antiferromagnetic free layer through voltage-controlled exchange coupling (VCEC). The switching current density, ~1.1x10^5 A/cm^2, is one order of magnitude lower than that of the best-reported spin-transfer torque devices. Theoretical results suggest that electric field induces a ferromagnetic-antiferromagnetic exchange coupling transition of the synthetic antiferromagnetic free layer and generates a field-like interlayer exchange coupling torque, which cause the bidirectional magnetization switching of p-MTJs. A preliminary benchmarking simulation estimates that VCEC dissipates an order of magnitude lower writing energy compared to spin-transfer torque at the 15-nm technology node. These results could eliminate the major obstacle in the development of spin memory devices beyond their embedded applications., Comment: 22 pages, 4 figures

Published
2019

2. Magnetic stray fields in nanoscale magnetic tunnel junctions

Author

Jenkins, Sarah, Meo, Andrea, Elliott, Luke, Piotrowski, Stephan K., Bapna, Mukund, Chantrell, Roy W., Majetich, Sara A., and Evans, Richard F. L.

Subjects
Condensed Matter - Materials Science
Abstract

The magnetic stray field is an unavoidable consequence of ferromagnetic devices and sensors leading to a natural asymmetry in magnetic properties. Such asymmetry is particularly undesirable for magnetic random access memory applications where the free layer can exhibit bias. Using atomistic dipole-dipole calculations we numerically simulate the stray magnetic field emanating from the magnetic layers of a magnetic memory device with different geometries. We find that edge effects dominate the overall stray magnetic field in patterned devices and that a conventional synthetic antiferromagnet structure is only partially able to compensate the field at the free layer position. A granular reference layer is seen to provide near-field flux closure while additional patterning defects add significant complexity to the stray field in nanoscale devices. Finally we find that the stray field from a nanoscale antiferromagnet is surprisingly non-zero arising from the imperfect cancellation of magnetic sublattices due to edge defects. Our findings provide an outline of the role of different layer structures and defects in the effective stray magnetic field in nanoscale magnetic random access memory devices and atomistic calculations provide a useful tools to study the stray field effects arising from a wide range of defects.

Published
2019
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4. Bipolar Electric-Field Switching of Perpendicular Magnetic Tunnel Junctions through Voltage-Controlled Exchange Coupling

Author

Zhang, Delin, primary, Bapna, Mukund, additional, Jiang, Wei, additional, Sousa, Duarte, additional, Liao, Yu-Ching, additional, Zhao, Zhengyang, additional, Lv, Yang, additional, Sahu, Protyush, additional, Lyu, Deyuan, additional, Naeemi, Azad, additional, Low, Tony, additional, Majetich, Sara A., additional, and Wang, Jian-Ping, additional

Published
2022
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14. Patterning of sub-50 nm perpendicular CoFeB/MgO-based magnetic tunnel junctions

Author

Tryputen, Larysa, primary, Tu, Kun-Hua, additional, Piotrowski, Stephan K, additional, Bapna, Mukund, additional, Majetich, Sara A, additional, Sun, Congli, additional, Voyles, Paul M, additional, Almasi, Hamid, additional, Wang, Weigang, additional, Vargas, Patricio, additional, Tresback, Jason S, additional, and Ross, Caroline A, additional

Published
2016
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17. Superparamagnetic perpendicular magnetic tunnel junctions for true random number generators.

Author

Parks, Bradley, Bapna, Mukund, Igbokwe, Julianne, Almasi, Hamid, Wang, Weigang, and Majetich, Sara A.

Subjects
*SUPERPARAMAGNETIC materials, *MAGNETIC tunnelling, *RANDOM number generators
Abstract

Superparamagnetic perpendicular magnetic tunnel junctions are fabricated and analyzed for use in random number generators. Time-resolved resistance measurements are used as streams of bits in statistical tests for randomness. Voltage control of the thermal stability enables tuning the average speed of random bit generation up to 70 kHz in a 60 nm diameter device. In its most efficient operating mode, the device generates random bits at an energy cost of 600 fJ/bit. A narrow range of magnetic field tunes the probability of a given state from 0 to 1, offering a means of probabilistic computing. [ABSTRACT FROM AUTHOR]

Published
2018
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23. Ultrafast light induced unusually broad transient absorption in the sub-bandgap region of GeSe2 thin film.

Author

Barik, A. R., Bapna, Mukund, Drabold, D. A., and Adarsh, K. V.

Subjects
*LIGHT absorption, *CHALCOGENIDE films, *THIN films, *BAND gaps, *WAVELENGTHS
Abstract

In this paper, we show for the first time that ultrafast light illumination can induce an unusually broad transient optical absorption (TA), spanning of ≈ 200 nm in the sub-bandgap region of chalcogenide GeSe2 thin films, which we interpret as being a manifestation of creation and annihilation of light induced defects. Further, TA in ultrashort time scales show a maximum at longer wavelength, however blue shifts as time evolves, which provides the first direct evidence of the multiple decay mechanisms of these defects. Detailed global analysis of the kinetic data clearly demonstrates that two and three decay constants are required to quantitatively model the experimental data at ps and ns respectively. [ABSTRACT FROM AUTHOR]

Published
2014
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24. Intensity-dependent transient photodarkening in visible and far infrared absorption spectra of As50Se50 thin film

Author

Barik, A.R., Bapna, Mukund, Naik, Ramakanta, Deshpande, Uday, Shripathi, T., and Adarsh, K.V.

Subjects
*PHOTODARKENING (Optics), *ABSORPTION spectra, *INFRARED spectra, *ARSENIC selenide, *THIN films, *TRANSIENTS (Dynamics), *BAND gaps
Abstract

Abstract: We report intensity-dependent transient photodarkening (TPD) in As50Se50 thin film when illuminated with sub-bandgap light of wavelength 671 nm. TPD is always accompanied by concurrent changes in the far infrared absorption spectrum and points out the structural units associated with such changes. Strikingly TPD and its kinetics show an exponential dependence on the pump beam intensity and we foresee that light intensity can be used as an effective tool to control such processes. [Copyright &y& Elsevier]

Published
2013
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25. Nanosecond pulse triggered absorption modulation in a-As50Se50 chalcogenide thin films.

Author

Bapna, Mukund, Barik, Amiya Ranjan, and Adarsh, K.V.

Subjects
*CHALCOGENIDE films, *LIGHT absorption, *ABSORPTION spectra, *LASER pulses, *BAND gaps, *SELENIDES
Abstract

Abstract: We present strong absorption modulation (ΔA≈3.5%) in As50Se50 chalcogenide thin film, using nanosecond pulses, as a new tool to tune the optical absorption spectrum in bandgap and sub-bandgap region. Interestingly, observed change in absorption persists only for few microseconds and thus allows modulating the absorption in a very short time scale. In our experiments, As50Se50 thin films were irradiated by 532nm laser having a pulse width of 5ns (control beam) with very low energy fluency of 3mJ/cm2 to modulate the absorption spectrum of as prepared As50Se50 thin film. Modulation of the sample absorption was monitored in the time window of 1ns–200μs using a probe beam in the wavelength range of 500 to 800nm, which covers the bandgap and sub-bandgap region of the sample. Absorption changes were observed to be largest (ΔA≈3.5%) in the wavelength range 550–700nm which decays very fast. a-As50Se50 thin films were found to exhibit full reversibility in transmission post-pulse-excitation, an observation that is unusual in chalcogenide systems. [Copyright &y& Elsevier]

Published
2013
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