The Experts below are selected from a list of 18087 Experts worldwide ranked by ideXlab platform
Gang Xiao - One of the best experts on this subject based on the ideXlab platform.
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magnetotransport and electronic noise in superparamagnetic magnetic Tunnel Junctions
2019Co-Authors: Yiou Zhang, Guanyang He, Xixiang Zhang, Gang XiaoAbstract:We have investigated the magnetotransport and noise properties of magnetic Tunnel Junctions incorporating a superparamagnetic free layer, in a wide temperature range from 150 K to 400 K. Both 1/f noise and sensitivity reach the maximum near the blocking temperature of the superparamagnetic transition. The smooth change of noise around the blocking temperature is attributed to size distribution of nanoclusters comprising the free layer. The best detectability ( 40 nT / H z at 1 Hz) is achieved at 350 K. In ferromagnetic and superparamagnetic states, 1/f noise follows different scaling relations with respect to sensitivity. The change of scaling law is explained by thermodynamics of the nanoclusters.We have investigated the magnetotransport and noise properties of magnetic Tunnel Junctions incorporating a superparamagnetic free layer, in a wide temperature range from 150 K to 400 K. Both 1/f noise and sensitivity reach the maximum near the blocking temperature of the superparamagnetic transition. The smooth change of noise around the blocking temperature is attributed to size distribution of nanoclusters comprising the free layer. The best detectability ( 40 nT / H z at 1 Hz) is achieved at 350 K. In ferromagnetic and superparamagnetic states, 1/f noise follows different scaling relations with respect to sensitivity. The change of scaling law is explained by thermodynamics of the nanoclusters.
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effect of film roughness in mgo based magnetic Tunnel Junctions
2006Co-Authors: Weifeng Shen, Dipanjan Mazumdar, Xiaojing Zou, Xiaoyong Liu, B D Schrag, Gang XiaoAbstract:We have systematically investigated the dependence of Tunnel magnetoresistance in MgO-based magnetic Tunnel Junctions as a function of Ar pressure during sputtering. The MgO surface roughness, and therefore device magnetoresistance, depends strongly on Ar gas pressure. Magnetoresistance of up to 236% was achieved at room temperature after thermal annealing at 425°C and with optimal sputtering conditions. The long mean free path of target atoms at low background pressures increases their kinetic energy at the substrate surface, resulting in smooth surface morphology and correspondingly improved device performance.
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electronic noise in magnetic Tunnel Junctions
1999Co-Authors: Snorri Ingvarsson, R A Wanner, A C Marley, K P Roche, W. J. Gallagher, P L Trouilloud, Yu Lu, Gang Xiao, S S P ParkinAbstract:We have studied bias and magnetic field dependence of voltage noise in metallic magnetic Tunnel Junctions with areal dimensions on the order of 1 μm. We generally observe noise with Gaussian amplitude distribution and pure 1/f power spectra at low frequencies. The 1/f noise scales with bias voltage as V2. Two kinds of deviations from this low frequency behavior have been observed. One is at fixed magnetic field when the junction bias reaches above a critical value, the other occurs at a fixed bias when the external magnetic field brings the sample to certain magnetic configurations. In both cases the noise spectra become dominated by Lorentzian noise and in both cases we have observed two level fluctuators in the time domain. We attribute the bias dependent noise to charge traps in the Tunnel barrier. The field dependent noise is associated with the switching of the magnetization direction of portions of the top electrode, which we believe to be reversible.
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microstructured magnetic Tunnel Junctions invited
1997Co-Authors: W. J. Gallagher, A C Marley, K P Roche, S S P Parkin, X P Bian, R A Altman, S A Rishton, C Jahnes, T M Shaw, Gang XiaoAbstract:We have used a simple self-aligned process to fabricate magnetic Tunnel Junctions down to submicron sizes. Optical and electron-beam lithographies were used to cover a range of areas spanning five orders of magnitude. The bottom magnetic electrodes (Co or permalloy) in our Junctions were exchange biased by an antiferromagnetic layer (MnFe). The top electrodes were made of soft magnetic materials (Co or permalloy). We have consistently obtained large magnetoresistance ratios (15%–22%) at room temperature and in fields of a few tens of Oe. The shape of the field response of the magnetoresistance was varied from smooth to highly hysteretic by adjusting the shape anisotropy of one junction electrode.
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magnetic Tunnel Junctions fabricated at tenth micron dimensions by electron beam lithography
1997Co-Authors: S A Rishton, A C Marley, W. J. Gallagher, Gang Xiao, X P Bian, R A Altman, C Jahnes, R Viswanathan, S S P ParkinAbstract:Abstract Magnetic Tunnel Junctions consisting of permalloy and cobalt thin film electrodes, separated by a thin aluminum oxide Tunnel barrier, have been fabricated by e-beam lithography at dimensions down to 120 nanometers. The devices are fabricated by sputter deposition and ion milling. They exhibit magnetoresistances of up to 22% at room temperature. Evidence of individual domain switching is observed. The smaller Junctions have resistances in the kilohm range, which are easily measured, leading to the possibility of sensing and microelectronic applications.
Evgeny Y. Tsymbal - One of the best experts on this subject based on the ideXlab platform.
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Tunneling Anisotropic Magnetoresistance in Ferroelectric Tunnel Junctions
2019Co-Authors: Artem Alexandrov, M. Ye. Zhuravlev, Evgeny Y. TsymbalAbstract:Using a simple quantum-mechanical model, we explore a Tunneling anisotropic magnetoresistance (TAMR) effect in ferroelectric Tunnel Junctions (FTJs) with a ferromagnetic electrode and a ferroelectric barrier layer, which spontaneous polarization gives rise to the Rashba and Dresselhaus spin-orbit coupling (SOC). For realistic parameters of the model, we predict sizable TAMR measurable experimentally. For asymmetric FTJs, which electrodes have different work functions, the built-in electric field affects the SOC parameters and leads to TAMR dependent on ferroelectric polarization direction. The SOC change with polarization switching affects Tunneling conductance, revealing a new mechanism of Tunneling electroresistance (TER). These results demonstrate new functionalities of FTJs which can be explored experimentally and used in electronic devices.
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ferroelectric and multiferroic Tunnel Junctions
2012Co-Authors: Evgeny Y. Tsymbal, M Bibes, Alexei Gruverman, Vincent Garcia, Alain BarthelemyAbstract:The phenomenon of electron Tunneling has been known since the advent of quantum mechanics, but continues to enrich our understanding of many fields of physics, as well as creating sub-fields on its own. Spin-dependent Tunneling in magnetic Tunnel Junctions has aroused considerable interest and development. In parallel with this endeavor, recent advances in thin-film ferroelectrics have demonstrated the possibility of achieving stable and switchable ferroelectric polarization in nanometer-thick films. This discovery opened the possibility of using thin-film ferroelectrics as barriers in magnetic Tunnel Junctions, thus merging the fields of magnetism, ferroelectricity, and spin-polarized transport into an exciting and promising area of novel research. Nowadays, this research has become an important constituent of a broader effort in multiferroic materials and heterostructures that involves rich fundamental science and offers a potential for applications in novel multifunctional devices. The purpose of this article is to review recent developments in ferroelectric and multiferroic Tunnel Junctions. Starting from the concept of electron Tunneling, we first discuss the key properties of magnetic Tunnel Junctions and then assess key functional characteristics of ferroelectric and multiferroic Tunnel Junctions. We discuss the recent demonstrations of giant resistive switching observed in ferroelectric Tunnel Junctions and the new concept of electrically controlling the spin polarization in magnetic Tunnel Junctions with a ferroelectric Tunnel barrier.
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Tunneling electroresistance effect in ferroelectric Tunnel Junctions at the nanoscale
2009Co-Authors: Alexei Gruverman, Ye. M. Zhuravlev, Yong Wang, Ho Won Jang, C M Folkman, D A Felker, M S Rzchowski, C B Eom, Evgeny Y. TsymbalAbstract:Using a set of scanning probe microscopy techniques, we demonstrate the reproducible Tunneling electroresistance effect on nanometer-thick epitaxial BaTiO3 single-crystalline thin films on SrRuO3 bottom electrodes. Correlation between ferroelectric and electronic transport properties is established by direct nanoscale visualization and control of polarization and Tunneling current. The obtained results show a change in resistance by about 2 orders of magnitude upon polarization reversal on a lateral scale of 20 nm at room temperature. These results are promising for employing ferroelectric Tunnel Junctions in nonvolatile memory and logic devices.
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Tunneling electroresistance effect in ferroelectric Tunnel Junctions at the nanoscale
2009Co-Authors: Alexei Gruverman, Ye. M. Zhuravlev, Yong Wang, Ho Won Jang, C M Folkman, D A Felker, M S Rzchowski, C B Eom, Evgeny Y. TsymbalAbstract:Stable and switchable polarization of ferroelectric materials opens a possibility to electrically control their functional behavior. A particularly promising approach is to employ ferroelectric Tunnel Junctions where the polarization reversal in a ferroelectric barrier changes the Tunneling current across the junction. Here, we demonstrate the reproducible Tunneling electroresistance effect using a combination of Piezoresponse Force Microscopy (PFM) and Conducting Atomic Force Microscopy (C-AFM) techniques on nanometer-thick epitaxial BaTiO3 single crystal thin films on SrRuO3 bottom electrodes. Correlation between ferroelectric and electronic transport properties is established by the direct nanoscale visualization and control of polarization and Tunneling current in BaTiO3 films. The obtained results show a change in resistance by about two orders of magnitude upon polarization reversal on a lateral scale of 20 nm at room temperature. These results are promising for employing ferroelectric Tunnel Junctions in non-volatile memory and logic devices, not involving charge as a state variable.
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magnetic Tunnel Junctions with ferroelectric barriers prediction of four resistance states from first principles
2009Co-Authors: Julian Velev, Chungang Duan, J D Burton, Alexander Smogunov, Manish K Niranjan, Erio Tosatti, S S Jaswal, Evgeny Y. TsymbalAbstract:Magnetic Tunnel Junctions (MTJs), composed of two ferromagnetic electrodes separated by a thin insulating barrier layer, are currently used in spintronic devices, such as magnetic sensors and magnetic random access memories. Recently, driven by demonstrations of ferroelectricity at the nanoscale, thin-film ferroelectric barriers were proposed to extend the functionality of MTJs. Due to the sensitivity of conductance to the magnetization alignment of the electrodes (Tunneling magnetoresistance) and the polarization orientation in the ferroelectric barrier (Tunneling electroresistance), these multiferroic Tunnel Junctions (MFTJs) may serve as four-state resistance devices. On the basis of first-principles calculations, we demonstrate four resistance states in SrRuO3/BaTiO3/SrRuO3 MFTJs with asymmetric interfaces. We find that the resistance of such a MFTJ is significantly changed when the electric polarization of the barrier is reversed and/or when the magnetizations of the electrodes are switched from para...
Siddharth Rajan - One of the best experts on this subject based on the ideXlab platform.
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design and demonstration of ultra wide bandgap algan Tunnel Junctions
2016Co-Authors: Yuewei Zhang, Sriram Krishnamoorthy, Fatih Akyol, A A Allerman, Michael W Moseley, Andrew M Armstrong, Siddharth RajanAbstract:Ultra violet light emitting diodes (UV LEDs) face critical limitations in both the injection efficiency and the light extraction efficiency due to the resistive and absorbing p-type contact layers. In this work, we investigate the design and application of polarization engineered Tunnel Junctions for ultra-wide bandgap AlGaN (Al mole fraction >50%) materials towards highly efficient UV LEDs. We demonstrate that polarization-induced three dimensional charge is beneficial in reducing Tunneling barriers especially for high composition AlGaN Tunnel Junctions. The design of graded Tunnel junction structures could lead to low Tunneling resistance below 10−3 Ω cm2 and low voltage consumption below 1 V (at 1 kA/cm2) for high composition AlGaN Tunnel Junctions. Experimental demonstration of 292 nm emission was achieved through non-equilibrium hole injection into wide bandgap materials with bandgap energy larger than 4.7 eV, and detailed modeling of Tunnel Junctions shows that they can be engineered to have low res...
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low resistance gan ingan gan Tunnel Junctions
2013Co-Authors: Sriram Krishnamoorthy, Fatih Akyol, Pil Sung Park, Siddharth RajanAbstract:Enhanced interband Tunnel injection of holes into a p-n junction is demonstrated using p-GaN/InGaN/n-GaN Tunnel Junctions with a specific resistivity of 1.2 × 10−4 Ω cm2. The design methodology and low-temperature characteristic of these Tunnel Junctions are discussed, and insertion into a p-n junction device is described. Applications of Tunnel Junctions in III-nitride optoelectronics devices are explained using energy band diagrams. The lower bandgap and polarization fields reduce Tunneling barrier, eliminating the need for ohmic contacts to p-type GaN. This demonstration of efficient Tunnel injection of carriers in III-nitrides can lead to a replacement of existing resistive p-type contact material in light emitters with Tunneling contact layers requiring very little metal footprint on the surface, resulting in enhanced light extraction.
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low resistance gan ingan gan Tunnel Junctions
2012Co-Authors: Sriram Krishnamoorthy, Fatih Akyol, Pil Sung Park, Siddharth RajanAbstract:Enhanced interband Tunnel injection of holes into a PN junction is demonstrated using P-GaN/InGaN/N-GaN Tunnel Junctions with a specific resistivity of 1.2 X 10-4 {\Omega} cm2. The design methodology and low-temperature characteristic of these Tunnel Junctions is discussed, and insertion into a PN junction device is described. Applications of Tunnel Junctions in III-nitride optoelectronics devices are explained using energy band diagrams. The lower band gap and polarization fields reduce Tunneling barrier, eliminating the need for ohmic contacts to p-type GaN. This demonstration of efficient Tunnel injection of carriers in III-Nitrides can lead to a replacement of existing resistive p-type contact material in light emitters with Tunneling contact layers, requiring very little metal footprint on the surface, resulting in enhanced light extraction from top emitting emitters.
C. Park - One of the best experts on this subject based on the ideXlab platform.
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co pt multilayer based magnetic Tunnel Junctions using perpendicular magnetic anisotropy
2008Co-Authors: Jeongheon Park, C. Park, Tae Hee Jeong, M T Moneck, Noel T Nufer, Jiangang ZhuAbstract:Magnetic Tunnel Junctions that utilize perpendicular magnetic anisotropy have attracted growing attention due to their potential for higher storage densities in future high capacity magnetic memory applications. In this study, we present an experimental demonstration of magnetic Tunnel Junctions composed of perpendicularly magnetized Co∕Pt multilayer electrodes and an AlOx Tunnel barrier. The emphasis has been on how to maximize the thickness of the Co layers adjacent to the Tunnel barrier while still magnetized perpendicularly for possible spin torque utilization in future applications. It is found that the thickness ratio between the Co and Pt layers and the number of bilayers were significant parameters to customize the magnetic properties. The difference between the switching fields of the soft and the hard layers can be adjusted by the number of repeats of the Co∕Pt bilayers. The measured hysteresis shows virtually zero exchange coupling between the two layers through the Tunnel barrier. Measured Tunneling magnetoresistance ratio of the fabricated submicron-size Tunnel Junctions ranges from 10% to 15% at room temperature.
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co pt multilayer based magnetic Tunnel Junctions using perpendicular magnetic anisotropy
2008Co-Authors: Jeongheon Park, C. Park, Tae Hee Jeong, M T Moneck, Noel T Nufer, Jiangang ZhuAbstract:Magnetic Tunnel Junctions that utilize perpendicular magnetic anisotropy have attracted growing attention due to their potential for higher storage densities in future high capacity magnetic memory applications. In this study, we present an experimental demonstration of magnetic Tunnel Junctions composed of perpendicularly magnetized Co∕Pt multilayer electrodes and an AlOx Tunnel barrier. The emphasis has been on how to maximize the thickness of the Co layers adjacent to the Tunnel barrier while still magnetized perpendicularly for possible spin torque utilization in future applications. It is found that the thickness ratio between the Co and Pt layers and the number of bilayers were significant parameters to customize the magnetic properties. The difference between the switching fields of the soft and the hard layers can be adjusted by the number of repeats of the Co∕Pt bilayers. The measured hysteresis shows virtually zero exchange coupling between the two layers through the Tunnel barrier. Measured tun...
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Magnetic Tunnel Junctions
2006Co-Authors: J. Zhu, C. ParkAbstract:Fueled by the ever-increasing demand for larger hard disk drive storage capacities, extensive research over the past decade has resulted in the development of AlOx- and TiOx-based magnetic Tunnel Junctions that exhibit a large magnetoresistive effect at room temperature. As their commercialization in various applications begins, a new type of magnetic Tunnel junction with a crystalline MgO Tunnel barrier has emerged that shows a much larger room-temperature magnetoresistive effect. We present a brief overview of the development of magnetic Tunnel Junctions, introducing the underlying physics. We also discuss two important commercial applications: read sensors in hard disk drives and memory elements in magnetoresistive random access memory. An emphasis is placed on the material aspects of magnetic Tunnel Junctions.
Jordan A. Katine - One of the best experts on this subject based on the ideXlab platform.
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voltage induced ferromagnetic resonance in magnetic Tunnel Junctions
2012Co-Authors: J. Zhu, Graham Rowlands, Pramey Upadhyaya, Juergen Langer, Pedram Khalili Amiri, Juan G Alzate, Jordan A. Katine, Zheng Duan, Y.j. Chen, Kang L WangAbstract:We demonstrate excitation of ferromagnetic resonance in CoFeB/MgO/CoFeB magnetic Tunnel Junctions (MTJs) by the combined action of voltage-controlled magnetic anisotropy (VCMA) and spin transfer torque (ST). Our measurements reveal that GHz-frequency VCMA torque and ST in low-resistance MTJs have similar magnitudes, and thus that both torques are equally important for understanding high-frequency voltage-driven magnetization dynamics in MTJs. As an example, we show that VCMA can increase the sensitivity of an MTJ-based microwave signal detector to the sensitivity level of semiconductor Schottky diodes.
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Voltage-induced switching of nanoscale magnetic Tunnel Junctions
2012Co-Authors: Juan G Alzate, Pramey Upadhyaya, Jordan A. Katine, J. Zhu, J Langer, P. Khalili Amiri, S. S. Cherepov, Mark Lewis, Richard Dorrance, Kosmas GalatsisAbstract:We demonstrate voltage-induced (non-STT) switching of nanoscale, high resistance voltage-controlled magnetic Tunnel Junctions (VMTJs) with pulses down to 10 ns. We show ∼10x reduction in switching energies (compared to STT) with leakage currents < 105 A/cm2. Switching dynamics, from quasi-static to the nanosecond regime, are studied in detail. Finally, a strategy for eliminating the need for external magnetic-fields, where switching is performed by set/reset voltages of different amplitudes but same polarity, is proposed and verified experimentally.
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switching current reduction using perpendicular anisotropy in cofeb mgo magnetic Tunnel Junctions
2011Co-Authors: Khalili P Amiri, Graham Rowlands, Jian Ping Wang, I N Krivorotov, Zhongming Zeng, J Langer, Hui Zhao, Yujin Chen, Hongwen Jiang, Jordan A. KatineAbstract:We present in-plane CoFeB–MgO magnetic Tunnel Junctions with perpendicular magnetic anisotropy in the free layer to reduce the spin transfer induced switching current. The Tunneling magnetoresistance ratio, resistance-area product, and switching current densities are compared in magnetic Tunnel Junctions with different CoFeB compositions. The effects of CoFeB free layer thickness on its magnetic anisotropy and current-induced switching characteristics are studied by vibrating sample magnetometry and electrical transport measurements on patterned elliptical nanopillar devices. Switching current densities ∼4 MA/cm2 are obtained at 10 ns write times.
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spin transfer effects in nanoscale magnetic Tunnel Junctions
2004Co-Authors: G D Fuchs, I N Krivorotov, N C Emley, R A Buhrman, D C Ralph, P M Braganca, E M Ryan, S I Kiselev, J C Sankey, Jordan A. KatineAbstract:We report measurements of magnetic switching and steady-state magnetic precession driven by spin-polarized currents in nanoscale magnetic Tunnel Junctions with low-resistance, <5Ωμm2, barriers. The current densities required for magnetic switching are similar to values for all-metallic spin-valve devices. In the Tunnel Junctions, spin-transfer-driven switching can occur at voltages that are high enough to quench the Tunnel magnetoresistance, demonstrating that the current remains spin polarized at these voltages.
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spin transfer effects in nanoscale magnetic Tunnel Junctions
2004Co-Authors: G D Fuchs, Jordan A. Katine, I N Krivorotov, N C Emley, D C Ralph, P M Braganca, E M Ryan, S I Kiselev, J C Sankey, R A BuhrmanAbstract:We report measurements of magnetic switching and steady-state magnetic precession driven by spin-polarized currents in nanoscale magnetic Tunnel Junctions with low-resistance, < 5 Ohm-micron-squared, barriers. The current densities required for magnetic switching are similar to values for all-metallic spin-valve devices. In the Tunnel Junctions, spin-transfer-driven switching can occur at voltages that are high enough to quench the Tunnel magnetoresistance, demonstrating that the current remains spin-polarized at these voltages.
