The Experts below are selected from a list of 5790 Experts worldwide ranked by ideXlab platform
Masaaki Tanaka - One of the best experts on this subject based on the ideXlab platform.
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large current modulation and Tunneling Magnetoresistance change by a side gate electric field in a gamnas based vertical spin metal oxide semiconductor field effect transistor
Scientific Reports, 2018Co-Authors: Toshiki Kanaki, Shinobu Ohya, Hiroki Yamasaki, Tomohiro Koyama, Daichi Chiba, Masaaki TanakaAbstract:A vertical spin metal-oxide-semiconductor field-effect transistor (spin MOSFET) is a promising low-power device for the post scaling era. Here, using a ferromagnetic-semiconductor GaMnAs-based vertical spin MOSFET with a GaAs channel layer, we demonstrate a large drain-source current IDS modulation by a gate-source voltage VGS with a modulation ratio up to 130%, which is the largest value that has ever been reported for vertical spin field-effect transistors thus far. We find that the electric field effect on indirect Tunneling via defect states in the GaAs channel layer is responsible for the large IDS modulation. This device shows a Tunneling Magnetoresistance (TMR) ratio up to ~7%, which is larger than that of the planar-type spin MOSFETs, indicating that IDS can be controlled by the magnetization configuration. Furthermore, we find that the TMR ratio can be modulated by VGS. This result mainly originates from the electric field modulation of the magnetic anisotropy of the GaMnAs ferromagnetic electrodes as well as the potential modulation of the nonmagnetic semiconductor GaAs channel layer. Our findings provide important progress towards high-performance vertical spin MOSFETs.
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fe concentration dependence of Tunneling Magnetoresistance in magnetic tunnel junctions using group iv ferromagnetic semiconductor gefe
AIP Advances, 2017Co-Authors: Kosuke Takiguchi, Masaaki Tanaka, Yuki K Wakabayashi, Kohei Okamoto, Shinobu OhyaAbstract:Group-IV-based ferromagnetic semiconductor Ge1−xFex (GeFe) is one of the most promising materials for spin injection/detection in Si and Ge. In this paper, we demonstrate a systematic study of Tunneling Magnetoresistance (TMR) in magnetic tunnel junctions (MTJs) composed of Fe/MgO/Ge1−xFex with various Fe concentrations (x = 0.065, 0.105, 0.140, and 0.175). With increasing x, the TMR ratio increases up to 1.5% when x≤ 0.105, and it decreases when x> 0.105. This is the first observation of the TMR ratio over 1% in MTJs containing a group-IV ferromagnetic semiconductor. With increasing x, while the Curie temperature of GeFe increases, the MgO surface becomes rougher, which is thought to be the cause of the upper limit of the TMR ratio. The quality of the MgO layer on GeFe is an important factor for further improvement of TMR in Fe/MgO/GeFe MTJs.
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quantum size effect and Tunneling Magnetoresistance in ferromagnetic semiconductor quantum heterostructures
Physical Review B, 2007Co-Authors: Shinobu Ohya, Yosuke Mizuno, Masaaki TanakaAbstract:We report on the resonant Tunneling effect and the increase of Tunneling Magnetoresistance (TMR) induced by it in ferromagnetic-semiconductor GaMnAs quantum-well heterostructures. The observed quantum levels of the GaMnAs quantum well were successfully explained by the valence-band kp model with the p-d exchange interaction. It was also found that the Fermi level of the electrode injecting carriers is important to observe resonant Tunneling in this system.
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large Tunneling Magnetoresistance in gamnas alas gamnas ferromagnetic semiconductor tunnel junctions
Physical Review Letters, 2001Co-Authors: Masaaki Tanaka, Y HigoAbstract:We have observed very large Tunneling Magnetoresistance (TMR) in epitaxially grown ${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{As}/\mathrm{AlAs}/{\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{As}$ ferromagnetic semiconductor tunnel junctions. Large TMR ratios more than $70%$ (maximum $75%$) were obtained in junctions with a very thin ( $\ensuremath{\le}1.6\mathrm{nm}$) AlAs tunnel barrier when the magnetic field was applied along the $[100]$ axis in the film plane. The TMR was found to rapidly decrease with increasing barrier thickness, which is explained by calculations assuming that the parallel wave vector of carriers is conserved in Tunneling.
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anisotropic Tunneling Magnetoresistance in gamnas alas gamnas ferromagnetic semiconductor tunnel junctions
Journal of Applied Physics, 2001Co-Authors: Y Higo, H Shimizu, Masaaki TanakaAbstract:We have observed very large Tunneling Magnetoresistance (TMR) in Ga1−xMnxAs/AlAs/Ga1−xMnxAs ferromagnetic semiconductor tunnel junctions. A TMR ratio as high as 75% was obtained in a junction with a thin (1.5 nm) AlAs tunnel barrier when the magnetic field was applied along the [100] axis in the film plane. The TMR ratio decreased when the applied magnetic field direction was along the [110] and [110]. This anisotropic TMR was found to be explained by the single-domain theory assuming cubic magnetic anisotropy with the easy axis of 〈100〉, which is induced by the zincblende-type Ga1−xMnxAs crystal structure.
Stuart S P Parkin - One of the best experts on this subject based on the ideXlab platform.
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brillouin zone spin filtering mechanism of enhanced Tunneling Magnetoresistance and correlation effects in a co 0001 h bn co 0001 magnetic tunnel junction
Physical Review B, 2015Co-Authors: Sergey V Faleev, Stuart S P Parkin, O N MryasovAbstract:The 'Brillouin zone spin filtering' mechanism of enhanced Tunneling Magnetoresistance (TMR) is described for magnetic tunnel junctions (MTJ) and studied on an example of the MTJ with hcp Co electrodes and hexagonal BN (h-BN) spacer. Our calculations based on local density approximation of density functional theory (LDA-DFT) for Co(0001)/h-BN/Co(0001) MTJ predict high TMR in this device due to Brillouin zone filtering mechanism. Owning to the specific complex band structure of the h-BN the spin-dependent Tunneling conductance of the system is ultra-sensitive to small variations of the Fermi energy position inside the BN band gap. Doping of the BN and, consequentially, changing the Fermi energy position could lead to variation of the TMR by several orders of magnitude. We show also that taking into account correlation effects on beyond DFT level is required to accurately describe position of the Fermi level and thus transport propertied of the system. Our study suggests that new MTJ based on hcp Co-Pt or Co-Pd disordered alloy electrodes and p-doped hexagonal BN spacer is a promising candidate for the spin-transfer torque magnetoresistive random-access memory (STT-MRAM).
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brillouin zone spin filtering mechanism of enhanced Tunneling Magnetoresistance and correlation effects in a co 0001 h bn co 0001 magnetic tunnel junction
Physical Review B, 2015Co-Authors: Sergey V Faleev, Stuart S P Parkin, O N MryasovAbstract:The Brillouin zone spin filtering mechanism of enhanced Tunneling Magnetoresistance (TMR) is described for magnetic tunnel junctions (MTJs) and studied for an example of the MTJ with hcp Co electrodes and hexagonal BN $(h$-BN) spacer. Our calculations based on the local density approximation of density-functional theory (LDA-DFT) for $\text{Co}(0001)/h\text{-BN}/\text{Co}(0001)$ MTJ predict high TMR in this device due to Brillouin zone filtering mechanism. Owning to the specific complex band structure of the $h$-BN the spin-dependent Tunneling conductance of the system is ultrasensitive to small variations of the Fermi energy position inside the BN band gap. Doping of the BN and, consequentially, changing the Fermi energy position could lead to variation of the TMR by several orders of magnitude. We show also that taking into account correlation effects on beyond DFT level is required to accurately describe position of the Fermi level and thus transport properties of the system. Our study suggests that new MTJ based on hcp Co-Pt or Co-Pd disordered alloy electrodes and $p$-doped hexagonal BN spacer is a promising candidate for the spin-transfer torque magnetoresistive random-access memory.
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negative Tunneling Magnetoresistance by canted magnetization in mgo nio tunnel barriers
Physical Review Letters, 2011Co-Authors: Hyunsoo Yang, Seehun Yang, Mark Saeys, Andrivo Rusydi, Hiroyo Kawai, Titus Leo, David J Smith, Stuart S P ParkinAbstract:The influence of the insertion of an ultrathin NiO layer between the MgO barrier and the ferromagnetic electrodes in magnetic tunnel junctions has been investigated from measurements of the Tunneling Magnetoresistance and via x-ray magnetic circular dichroism (XMCD). The Magnetoresistance shows a high asymmetry with respect to bias voltage, giving rise to a negative value of up to -16% at 2.8 K. We attribute this effect to the formation of noncollinear spin structures at the interface of the NiO layer as inferred from XMCD measurements. The magnetic moments of the interface Ni atoms tilt from their easy axis due to exchange coupling with the neighboring ferromagnetic electrode, and the tilting angle decreases with increasing NiO thickness. The experimental observations are further supported by noncollinear spin density functional calculations.
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increased Tunneling Magnetoresistance using normally bcc cofe alloy electrodes made amorphous without glass forming additives
Physical Review Letters, 2009Co-Authors: Li Gao, Xin Jiang, Seehun Yang, Philip M Rice, Teya Topuria, Stuart S P ParkinAbstract:Using cross-section transmission electron microscopy we show that films of CoFe alloys, sandwiched between two conventional amorphous materials, are amorphous when less than $\ensuremath{\sim}25--30\text{ }\text{ }\AA{}$ thick. When these amorphous layers are integrated into magnetic tunnel junctions with amorphous alumina tunnel barriers, significantly higher Tunneling Magnetoresistance is found compared to when these layers are made crystalline (e.g., by heating or by thickening them). We postulate that this is likely due to changes in interfacial bonding at the alumina-CoFe interface. Indeed, x-ray emission spectroscopy shows a significant increase in the Fe, but not the Co, $3d$ density of states at the Fermi energy for thin amorphous CoFe layers.
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crossover from kondo assisted suppression to co Tunneling enhancement of Tunneling Magnetoresistance via ferromagnetic nanodots in mgo tunnel barriers
Nano Letters, 2008Co-Authors: Hyunsoo Yang, Seehun Yang, Stuart S P ParkinAbstract:The dependence of the Tunneling Magnetoresistance (TMR) of planar magnetic tunnel junctions on the size of magnetic nanodots incorporated within MgO tunnel barriers is explored. At low temperatures, in the Coulomb blockade (CB) regime, for smaller nanodots the conductance of the junction is increased at low bias consistent with Kondo-assisted Tunneling and the TMR is suppressed. For slightly larger nanodots but within the CB regime, the TMR is enhanced at low bias, consistent with co-Tunneling. Magnetic tunnel junctions (MTJ) exhibit giant Magnetoresistance in small magnetic fields that arises from the flow of spin-polarized current through an ultrathin tunnel barrier separating two magnetic electrodes. The current through an MTJ device depends on the magnetic orientation of the electrodes and is typically higher when the electrode moments are parallel than when they are antiparallel. It has recently been demonstrated that the spin polarization of the Tunneling current can be greatly enhanced by using crystalline tunnel barriers formed from MgO as compared with conventional amorphous barriers formed from alumina, due to spin filtering across the MgO layer. The magneto-transport properties of magnetic granular alloys and magnetic tunnel junction devices with magnetic nanodots embedded in amorphous dielectric matrices, and tunnel barriers, respectively, have been studied by several groups, but no systematic studies of the dependence on these properties on the nanodot size have been made.
O N Mryasov - One of the best experts on this subject based on the ideXlab platform.
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brillouin zone spin filtering mechanism of enhanced Tunneling Magnetoresistance and correlation effects in a co 0001 h bn co 0001 magnetic tunnel junction
Physical Review B, 2015Co-Authors: Sergey V Faleev, Stuart S P Parkin, O N MryasovAbstract:The 'Brillouin zone spin filtering' mechanism of enhanced Tunneling Magnetoresistance (TMR) is described for magnetic tunnel junctions (MTJ) and studied on an example of the MTJ with hcp Co electrodes and hexagonal BN (h-BN) spacer. Our calculations based on local density approximation of density functional theory (LDA-DFT) for Co(0001)/h-BN/Co(0001) MTJ predict high TMR in this device due to Brillouin zone filtering mechanism. Owning to the specific complex band structure of the h-BN the spin-dependent Tunneling conductance of the system is ultra-sensitive to small variations of the Fermi energy position inside the BN band gap. Doping of the BN and, consequentially, changing the Fermi energy position could lead to variation of the TMR by several orders of magnitude. We show also that taking into account correlation effects on beyond DFT level is required to accurately describe position of the Fermi level and thus transport propertied of the system. Our study suggests that new MTJ based on hcp Co-Pt or Co-Pd disordered alloy electrodes and p-doped hexagonal BN spacer is a promising candidate for the spin-transfer torque magnetoresistive random-access memory (STT-MRAM).
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brillouin zone spin filtering mechanism of enhanced Tunneling Magnetoresistance and correlation effects in a co 0001 h bn co 0001 magnetic tunnel junction
Physical Review B, 2015Co-Authors: Sergey V Faleev, Stuart S P Parkin, O N MryasovAbstract:The Brillouin zone spin filtering mechanism of enhanced Tunneling Magnetoresistance (TMR) is described for magnetic tunnel junctions (MTJs) and studied for an example of the MTJ with hcp Co electrodes and hexagonal BN $(h$-BN) spacer. Our calculations based on the local density approximation of density-functional theory (LDA-DFT) for $\text{Co}(0001)/h\text{-BN}/\text{Co}(0001)$ MTJ predict high TMR in this device due to Brillouin zone filtering mechanism. Owning to the specific complex band structure of the $h$-BN the spin-dependent Tunneling conductance of the system is ultrasensitive to small variations of the Fermi energy position inside the BN band gap. Doping of the BN and, consequentially, changing the Fermi energy position could lead to variation of the TMR by several orders of magnitude. We show also that taking into account correlation effects on beyond DFT level is required to accurately describe position of the Fermi level and thus transport properties of the system. Our study suggests that new MTJ based on hcp Co-Pt or Co-Pd disordered alloy electrodes and $p$-doped hexagonal BN spacer is a promising candidate for the spin-transfer torque magnetoresistive random-access memory.
Jiaqi Zhou - One of the best experts on this subject based on the ideXlab platform.
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large Tunneling Magnetoresistance in vse2 mos2 magnetic tunnel junction
ACS Applied Materials & Interfaces, 2019Co-Authors: Junfeng Qiao, Jiaqi Zhou, Chungang Duan, Arnaud Bournel, Kang L WangAbstract:Two-dimensional (2D) van der Waals (vdW) materials provide the possibility of realizing heterostructures with coveted properties. Here, we report a theoretical investigation of the vdW magnetic tunnel junction (MTJ) based on VSe2/MoS2 heterojunction, where the VSe2 monolayer acts as a ferromagnet with room-temperature ferromagnetism. We propose the concept of spin-orbit torque (SOT) vdW MTJ with reliable reading and efficient writing operations. The nonequilibrium study reveals a large Tunneling Magnetoresistance of 846% at 300 K, identifying significantly its parallel and antiparallel states. Thanks to the strong spin Hall conductivity of MoS2, SOT is promising for the magnetization switching of VSe2 free layer. Quantum-well states come into being and resonances appear in MTJ, suggesting that the voltage control can adjust transport properties effectively. The SOT vdW MTJ based on VSe2/MoS2 provides desirable performance and experimental feasibility, offering new opportunities for 2D spintronics.
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large Tunneling Magnetoresistance in vse2 mos2 magnetic tunnel junction
ACS Applied Materials & Interfaces, 2019Co-Authors: Kang L Wang, Jiaqi Zhou, Junfeng Qiao, Chungang Duan, Arnaud Bournel, Weisheng ZhaoAbstract:Two-dimensional (2D) van der Waals (vdW) materials provide the possibility of realizing heterostructures with coveted properties. Here, we report a theoretical investigation of the vdW magnetic tun...
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Large Tunneling Magnetoresistance in VSe2/MoS2 Magnetic Tunnel Junction
2019Co-Authors: Jiaqi Zhou, Kang L Wang, Junfeng Qiao, Chungang Duan, Arnaud Bournel, Weisheng ZhaoAbstract:Two-dimensional (2D) van der Waals (vdW) materials provide the possibility of realizing heterostructures with coveted properties. Here, we report a theoretical investigation of the vdW magnetic tunnel junction (MTJ) based on VSe2/MoS2 heterojunction, where the VSe2 monolayer acts as a ferromagnet with room-temperature ferromagnetism. We propose the concept of spin–orbit torque (SOT) vdW MTJ with reliable reading and efficient writing operations. The nonequilibrium study reveals a large Tunneling Magnetoresistance of 846% at 300 K, identifying significantly its parallel and antiparallel states. Thanks to the strong spin Hall conductivity of MoS2, SOT is promising for the magnetization switching of VSe2 free layer. Quantum-well states come into being and resonances appear in MTJ, suggesting that the voltage control can adjust transport properties effectively. The SOT vdW MTJ based on VSe2/MoS2 provides desirable performance and experimental feasibility, offering new opportunities for 2D spintronics
Sergey V Faleev - One of the best experts on this subject based on the ideXlab platform.
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heusler compounds with perpendicular magnetic anisotropy and large Tunneling Magnetoresistance
Physical Review Materials, 2017Co-Authors: Sergey V Faleev, Yari Ferrante, Jaewoo Jeong, Mahesh G Samant, Barbara Jones, S S P ParkinAbstract:In the present work we suggest a recipe for finding tetragonal Heusler compounds with perpendicular magnetic anisotropy (PMA) that also exhibit large Tunneling Magnetoresistance (TMR) when used as electrodes in magnetic tunnel junction devices with suitable Tunneling barrier materials. We performed density-functional theory calculations for 286 Heusler compounds and identified 116 stable tetragonal compounds. Ten of these compounds are predicted to have strong PMA and, simultaneously, exponentially increasing TMR with increasing Tunneling barrier thickness due to the so-called Brillouin zone spin filtering effect. Experimental measurements performed for 25 Heusler compounds theoretically identified as tetragonal show that ten of these compounds indeed have tetragonal structure with PMA.
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brillouin zone spin filtering mechanism of enhanced Tunneling Magnetoresistance and correlation effects in a co 0001 h bn co 0001 magnetic tunnel junction
Physical Review B, 2015Co-Authors: Sergey V Faleev, Stuart S P Parkin, O N MryasovAbstract:The 'Brillouin zone spin filtering' mechanism of enhanced Tunneling Magnetoresistance (TMR) is described for magnetic tunnel junctions (MTJ) and studied on an example of the MTJ with hcp Co electrodes and hexagonal BN (h-BN) spacer. Our calculations based on local density approximation of density functional theory (LDA-DFT) for Co(0001)/h-BN/Co(0001) MTJ predict high TMR in this device due to Brillouin zone filtering mechanism. Owning to the specific complex band structure of the h-BN the spin-dependent Tunneling conductance of the system is ultra-sensitive to small variations of the Fermi energy position inside the BN band gap. Doping of the BN and, consequentially, changing the Fermi energy position could lead to variation of the TMR by several orders of magnitude. We show also that taking into account correlation effects on beyond DFT level is required to accurately describe position of the Fermi level and thus transport propertied of the system. Our study suggests that new MTJ based on hcp Co-Pt or Co-Pd disordered alloy electrodes and p-doped hexagonal BN spacer is a promising candidate for the spin-transfer torque magnetoresistive random-access memory (STT-MRAM).
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brillouin zone spin filtering mechanism of enhanced Tunneling Magnetoresistance and correlation effects in a co 0001 h bn co 0001 magnetic tunnel junction
Physical Review B, 2015Co-Authors: Sergey V Faleev, Stuart S P Parkin, O N MryasovAbstract:The Brillouin zone spin filtering mechanism of enhanced Tunneling Magnetoresistance (TMR) is described for magnetic tunnel junctions (MTJs) and studied for an example of the MTJ with hcp Co electrodes and hexagonal BN $(h$-BN) spacer. Our calculations based on the local density approximation of density-functional theory (LDA-DFT) for $\text{Co}(0001)/h\text{-BN}/\text{Co}(0001)$ MTJ predict high TMR in this device due to Brillouin zone filtering mechanism. Owning to the specific complex band structure of the $h$-BN the spin-dependent Tunneling conductance of the system is ultrasensitive to small variations of the Fermi energy position inside the BN band gap. Doping of the BN and, consequentially, changing the Fermi energy position could lead to variation of the TMR by several orders of magnitude. We show also that taking into account correlation effects on beyond DFT level is required to accurately describe position of the Fermi level and thus transport properties of the system. Our study suggests that new MTJ based on hcp Co-Pt or Co-Pd disordered alloy electrodes and $p$-doped hexagonal BN spacer is a promising candidate for the spin-transfer torque magnetoresistive random-access memory.
