The Experts below are selected from a list of 8625 Experts worldwide ranked by ideXlab platform
Stuart S. P. Parkin - One of the best experts on this subject based on the ideXlab platform.
-
increased efficiency of current induced motion of chiral domain walls by interface engineering
Advanced Materials, 2021Co-Authors: Yicheng Guan, See-hun Yang, Xilin Zhou, Robin Blasing, Hakan Deniz, Stuart S. P. ParkinAbstract:Magnetic Racetrack devices are promising candidates for next-generation memories. These spintronic shift-register devices are formed from perpendicularly magnetized ferromagnet/heavy metal thin-film systems. Data are encoded in domain wall magnetic bits that have a chiral Neel structure that is stabilized by an interfacial Dzyaloshinskii-Moriya interaction. The bits are manipulated by spin currents generated from electrical currents that are passed through the heavy metal layers. Increased efficiency of the current-induced domain wall motion is a prerequisite for commercially viable Racetrack devices. Here, significantly increased efficiency with substantially lower threshold current densities and enhanced domain wall velocities is demonstrated by the introduction of atomically thin 4d and 5d metal "dusting" layers at the interface between the lower magnetic layer of the Racetrack (here cobalt) and platinum. The greatest efficiency is found for dusting layers of palladium and rhodium, just one monolayer thick, for which the domain wall's velocity is increased by up to a factor of 3.5. Remarkably, when the heavy metal layer is formed from the dusting layer material alone, the efficiency is rather reduced by an order of magnitude. The results point to the critical role of interface engineering for the development of efficient Racetrack memory devices.
-
magnetic antiskyrmions above room temperature in tetragonal heusler materials
Nature, 2017Co-Authors: Ajaya K Nayak, Vivek Kumar, P Werner, Eckhard Pippel, Roshnee Sahoo, Franoise Damay, Ulrich K Rosler, Claudia Felser, Stuart S. P. ParkinAbstract:Magnetic skyrmions are topologically stable, vortex-like objects surrounded by chiral boundaries that separate a region of reversed magnetization from the surrounding magnetized material. They are closely related to nanoscopic chiral magnetic domain walls, which could be used as memory and logic elements for conventional and neuromorphic computing applications that go beyond Moore’s law. Of particular interest is ‘Racetrack memory’, which is composed of vertical magnetic nanowires, each accommodating of the order of 100 domain walls, and that shows promise as a solid state, non-volatile memory with exceptional capacity and performance. Its performance is derived from the very high speeds (up to one kilometre per second) at which chiral domain walls can be moved with nanosecond current pulses in synthetic antiferromagnet Racetracks. Because skyrmions are essentially composed of a pair of chiral domain walls closed in on themselves, but are, in principle, more stable to perturbations than the component domain walls themselves, they are attractive for use in spintronic applications, notably Racetrack memory. Stabilization of skyrmions has generally been achieved in systems with broken inversion symmetry, in which the asymmetric Dzyaloshinskii–Moriya interaction modifies the uniform magnetic state to a swirling state. Depending on the crystal symmetry, two distinct types of skyrmions have been observed experimentally, namely, Bloch and Neel skyrmions. Here we present the experimental manifestation of another type of skyrmion—the magnetic antiskyrmion—in acentric tetragonal Heusler compounds with D$_{2d}$ crystal symmetry. Antiskyrmions are characterized by boundary walls that have alternating Bloch and Neel type as one traces around the boundary. A spiral magnetic ground-state, which propagates in the tetragonal basal plane, is transformed into an antiskyrmion lattice state under magnetic fields applied along the tetragonal axis over a wide range of temperatures. Direct imaging by Lorentz transmission electron microscopy shows field-stabilized antiskyrmion lattices and isolated antiskyrmions from 100 kelvin to well beyond room temperature, and zero-field metastable antiskyrmions at low temperatures. These results enlarge the family of magnetic skyrmions and pave the way to the engineering of complex bespoke designed skyrmionic structures.
-
domain wall velocities of up to 750 m s 1 driven by exchange coupling torque in synthetic antiferromagnets
Nature Nanotechnology, 2015Co-Authors: See-hun Yang, Kwangsu Ryu, Stuart S. P. ParkinAbstract:Racetrack memories made from synthetic antiferromagnetic structures with almost zero net magnetization allow for fast current-driven motion of domain walls.
-
enhanced stochasticity of domain wall motion in magnetic Racetracks due to dynamic pinning
Nature Communications, 2010Co-Authors: Xin Jiang, Luc Thomas, Masamitsu Hayashi, Rai Moriya, Bastiaan Bergman, C T Rettner, Stuart S. P. ParkinAbstract:Understanding the details of domain wall (DW) motion along magnetic Racetracks has drawn considerable interest in the past few years for their applications in non-volatile memory devices. The propagation of the DW is dictated by the interplay between its driving force, either field or current, and the complex energy landscape of the Racetrack. In this study, we use spin-valve nanowires to study field-driven DW motion in real time. By varying the strength of the driving magnetic field, the propagation mode of the DW can be changed from a simple translational mode to a more complex precessional mode. Interestingly, the DW motion becomes much more stochastic at the onset of this propagation mode. We show that this unexpected result is a consequence of an unsustainable gain in Zeeman energy of the DW, as it is driven faster by the magnetic field. As a result, the DW periodically releases energy and thereby becomes more susceptible to pinning by local imperfections in the Racetrack.
-
Magnetic domain-wall Racetrack memory
Science, 2008Co-Authors: Stuart S. P. Parkin, Masamitsu Hayashi, Luc ThomasAbstract:Recent developments in the controlled movement of domain walls in magnetic nanowires by short pulses of spin-polarized current give promise of a nonvolatile memory device with the high performance and reliability of conventional solid-state memory but at the low cost of conventional magnetic disk drive storage. The Racetrack memory described in this review comprises an array of magnetic nanowires arranged horizontally or vertically on a silicon chip. Individual spintronic reading and writing nanodevices are used to modify or read a train of ∼10 to 100 domain walls, which store a series of data bits in each nanowire. This Racetrack memory is an example of the move toward innately three-dimensional microelectronic devices.
Marko Loncar - One of the best experts on this subject based on the ideXlab platform.
-
microwave to optical conversion using lithium niobate thin film acoustic resonators
Optica, 2019Co-Authors: Linbo Shao, Smarak Maity, Neil Sinclair, Lu Zheng, Cleaven Chia, Amirhassan Shamsansari, Cheng Wang, Mian Zhang, Keji Lai, Marko LoncarAbstract:Acoustic or mechanical resonators have emerged as a promising means to mediate efficient microwave-to-optical conversion. Here, we demonstrate conversion of microwaves up to 4.5 GHz in frequency to 1500 nm wavelength light using optomechanical interactions on suspended thin-film lithium niobate. Our method uses an interdigital transducer that drives a freestanding 100 μm-long thin-film acoustic resonator to modulate light traveling in a Mach–Zehnder interferometer or Racetrack cavity. The strong microwave-to-acoustic coupling offered by the transducer in conjunction with the strong photoelastic, piezoelectric, and electro-optic effects of lithium niobate allows us to achieve a half-wave voltage of Vπ=4.6 V and Vπ=0.77 V for the Mach–Zehnder interferometer and Racetrack resonator, respectively. The acousto-optic Racetrack cavity exhibits an optomechanical single-photon coupling strength of 1.1 kHz. To highlight the versatility of our system, we also demonstrate a microwave photonic link with unitary gain, which refers to a 0 dB microwave power transmission over an optical channel. Our integrated nanophotonic platform, which leverages the compelling properties of lithium niobate, could help enable efficient conversion between microwave and optical fields.
-
microwave to optical conversion using lithium niobate thin film acoustic resonators
arXiv: Applied Physics, 2019Co-Authors: Linbo Shao, Smarak Maity, Neil Sinclair, Lu Zheng, Cleaven Chia, Amirhassan Shamsansari, Cheng Wang, Mian Zhang, Keji Lai, Marko LoncarAbstract:We demonstrate conversion of up to 4.5 GHz-frequency microwaves to 1500 nm-wavelength light using optomechanical interactions on suspended thin-film lithium niobate. Our method utilizes an interdigital transducer that drives a free-standing 100 $\mu$m-long thin-film acoustic resonator to modulate light travelling in a Mach-Zehnder interferometer or Racetrack cavity. Owing to the strong microwave-to-acoustic coupling offered by the transducer in conjunction with the strong photoelastic, piezoelectric, and electro-optic effects of lithium niobate, we achieve a half-wave voltage of $V_\pi$ = 4.6 V and $V_\pi$ = 0.77 V for the Mach-Zehnder interferometer and Racetrack resonator, respectively. The acousto-optic Racetrack cavity exhibits an optomechancial single-photon coupling strength of 1.1 kHz. Our integrated nanophotonic platform coherently leverages the compelling properties of lithium niobate to achieve microwave-to-optical transduction. To highlight the versatility of our system, we also demonstrate a lossless microwave photonic link, which refers to a 0 dB microwave power transmission over an optical channel.
-
high q optical nanocavities in bulk single crystal diamond
Conference on Lasers and Electro-Optics, 2014Co-Authors: Michael J Burek, Yiwen Chu, Madelaine S Z Liddy, Parth Patel, Jake Rochman, Mikhail D Lukin, Marko LoncarAbstract:Optical nanocavities (Racetrack resonators and photonic crystal cavities) are fabricated in bulk single-crystal diamond via angled-etching. Devices operating in the telecom band exhibited Q-factors exceeding 10^5, while devices in the visible yielded Q-factors approaching 10^4.
See-hun Yang - One of the best experts on this subject based on the ideXlab platform.
-
increased efficiency of current induced motion of chiral domain walls by interface engineering
Advanced Materials, 2021Co-Authors: Yicheng Guan, See-hun Yang, Xilin Zhou, Robin Blasing, Hakan Deniz, Stuart S. P. ParkinAbstract:Magnetic Racetrack devices are promising candidates for next-generation memories. These spintronic shift-register devices are formed from perpendicularly magnetized ferromagnet/heavy metal thin-film systems. Data are encoded in domain wall magnetic bits that have a chiral Neel structure that is stabilized by an interfacial Dzyaloshinskii-Moriya interaction. The bits are manipulated by spin currents generated from electrical currents that are passed through the heavy metal layers. Increased efficiency of the current-induced domain wall motion is a prerequisite for commercially viable Racetrack devices. Here, significantly increased efficiency with substantially lower threshold current densities and enhanced domain wall velocities is demonstrated by the introduction of atomically thin 4d and 5d metal "dusting" layers at the interface between the lower magnetic layer of the Racetrack (here cobalt) and platinum. The greatest efficiency is found for dusting layers of palladium and rhodium, just one monolayer thick, for which the domain wall's velocity is increased by up to a factor of 3.5. Remarkably, when the heavy metal layer is formed from the dusting layer material alone, the efficiency is rather reduced by an order of magnitude. The results point to the critical role of interface engineering for the development of efficient Racetrack memory devices.
-
An all-electrical magnetic logic gate that harnesses chirality between domains
Nature, 2020Co-Authors: See-hun YangAbstract:A NOT gate for magnetic Racetrack memory. Bits of a logic gate can be encoded by differently magnetized regions. A method has been developed in which the walls between these domains are manipulated electrically, rather than magnetically, to produce a logic gate.
-
domain wall velocities of up to 750 m s 1 driven by exchange coupling torque in synthetic antiferromagnets
Nature Nanotechnology, 2015Co-Authors: See-hun Yang, Kwangsu Ryu, Stuart S. P. ParkinAbstract:Racetrack memories made from synthetic antiferromagnetic structures with almost zero net magnetization allow for fast current-driven motion of domain walls.
Mehdi Asghari - One of the best experts on this subject based on the ideXlab platform.
-
high speed and compact silicon modulator based on a Racetrack resonator with a 1 v drive voltage
Optics Letters, 2010Co-Authors: Po Dong, Wei Qian, Hong Liang, Roshanak Shafiiha, Dazeng Feng, Ashok V Krishnamoorthy, Shirong Liao, Xin Wang, Xuezhe Zheng, Mehdi AsghariAbstract:Fast, compact, and power-efficient silicon microcavity electro-optic modulators are expected to be critical components for chip-level optical interconnects. It is highly desirable that these modulators can be driven by voltage swings of 1V or less to reduce power dissipation and make them compatible with voltage supply levels associated with current and future complementary metal-oxide-semiconductor technology nodes. Here, we present a silicon Racetrack resonator modulator that achieves over 8dB modulation depth at 12.5Gbps with a 1V swing. In addition, the use of a Racetrack resonator geometry relaxes the tight lithography resolution requirements typically associated with microring resonators and enhances the ability to use common lithographic optical techniques for their fabrication.
-
thermally tunable silicon Racetrack resonators with ultralow tuning power
Optics Express, 2010Co-Authors: Po Dong, Wei Qian, Hong Liang, Roshanak Shafiiha, Dazeng Feng, John E Cunningham, Ashok V Krishnamoorthy, Mehdi AsghariAbstract:We present thermally tunable silicon Racetrack resonators with an ultralow tuning power of 2.4 mW per free spectral range. The use of free-standing silicon Racetrack resonators with undercut structures significantly enhances the tuning efficiency, with one order of magnitude improvement of that for previously demonstrated thermo-optic devices without undercuts. The 10%-90% switching time is demonstrated to be ~170 µs. Such low-power tunable micro-resonators are particularly useful as multiplexing devices and wavelength-tunable silicon microcavity modulators.
Linbo Shao - One of the best experts on this subject based on the ideXlab platform.
-
microwave to optical conversion using lithium niobate thin film acoustic resonators
Optica, 2019Co-Authors: Linbo Shao, Smarak Maity, Neil Sinclair, Lu Zheng, Cleaven Chia, Amirhassan Shamsansari, Cheng Wang, Mian Zhang, Keji Lai, Marko LoncarAbstract:Acoustic or mechanical resonators have emerged as a promising means to mediate efficient microwave-to-optical conversion. Here, we demonstrate conversion of microwaves up to 4.5 GHz in frequency to 1500 nm wavelength light using optomechanical interactions on suspended thin-film lithium niobate. Our method uses an interdigital transducer that drives a freestanding 100 μm-long thin-film acoustic resonator to modulate light traveling in a Mach–Zehnder interferometer or Racetrack cavity. The strong microwave-to-acoustic coupling offered by the transducer in conjunction with the strong photoelastic, piezoelectric, and electro-optic effects of lithium niobate allows us to achieve a half-wave voltage of Vπ=4.6 V and Vπ=0.77 V for the Mach–Zehnder interferometer and Racetrack resonator, respectively. The acousto-optic Racetrack cavity exhibits an optomechanical single-photon coupling strength of 1.1 kHz. To highlight the versatility of our system, we also demonstrate a microwave photonic link with unitary gain, which refers to a 0 dB microwave power transmission over an optical channel. Our integrated nanophotonic platform, which leverages the compelling properties of lithium niobate, could help enable efficient conversion between microwave and optical fields.
-
microwave to optical conversion using lithium niobate thin film acoustic resonators
arXiv: Applied Physics, 2019Co-Authors: Linbo Shao, Smarak Maity, Neil Sinclair, Lu Zheng, Cleaven Chia, Amirhassan Shamsansari, Cheng Wang, Mian Zhang, Keji Lai, Marko LoncarAbstract:We demonstrate conversion of up to 4.5 GHz-frequency microwaves to 1500 nm-wavelength light using optomechanical interactions on suspended thin-film lithium niobate. Our method utilizes an interdigital transducer that drives a free-standing 100 $\mu$m-long thin-film acoustic resonator to modulate light travelling in a Mach-Zehnder interferometer or Racetrack cavity. Owing to the strong microwave-to-acoustic coupling offered by the transducer in conjunction with the strong photoelastic, piezoelectric, and electro-optic effects of lithium niobate, we achieve a half-wave voltage of $V_\pi$ = 4.6 V and $V_\pi$ = 0.77 V for the Mach-Zehnder interferometer and Racetrack resonator, respectively. The acousto-optic Racetrack cavity exhibits an optomechancial single-photon coupling strength of 1.1 kHz. Our integrated nanophotonic platform coherently leverages the compelling properties of lithium niobate to achieve microwave-to-optical transduction. To highlight the versatility of our system, we also demonstrate a lossless microwave photonic link, which refers to a 0 dB microwave power transmission over an optical channel.
