arXiv subjects

Jian-Ping Wang

Publications and source records attributed to Jian-Ping Wang.

At least 73 records · Page 4Linked to original sources

arXiv2019

Magnetic Nanoparticle Relaxation Dynamics-based Magnetic Particle Spectroscopy (MPS) for Rapid and Wash-free Molecular Sensing

Magnetic nanoparticles (MNPs) have been extensively used as contrasts and tracers for bioimaging, heating sources for tumor therapy, carriers for controlled drug delivery, and labels for magnetic immunoassays. Here, we describe a MNP relaxation dynamics-based magnetic particle spectroscopy (MPS) method for the quantitative detection of molecular biomarkers. In MPS measurements, the harmonics of oscillating MNPs are recorded and used as a metric for the freedom of rotational motion, which indicates the bound states of the MNPs. These harmonics can be collected from microgram quantities of iron oxide nanoparticles within 10 seconds. Using a streptavidin-biotin binding system, we demonstrate the feasibility of using MPS to sense these molecular interactions, showing this method is able to achieve rapid, wash-free bioassays, and is suitable for future point-of-care (POC), sensitive, and versatile diagnosis.

physics.app-ph↗

arXiv2019

A Machine Learning Accelerator In-Memory for Energy Harvesting

There is increasing demand to bring machine learning capabilities to low power devices. By integrating the computational power of machine learning with the deployment capabilities of low power devices, a number of new applications become possible. In some applications, such devices will not even have a battery, and must rely solely on energy harvesting techniques. This puts extreme constraints on the hardware, which must be energy efficient and capable of tolerating interruptions due to power outages. Here, as a representative example, we propose an in-memory support vector machine learning accelerator utilizing non-volatile spintronic memory. The combination of processing-in-memory and non-volatility provides a key advantage in that progress is effectively saved after every operation. This enables instant shut down and restart capabilities with minimal overhead. Additionally, the operations are highly energy efficient leading to low power consumption.

cs.ET↗

arXiv2019

PIMBALL: Binary Neural Networks in Spintronic Memory

Neural networks span a wide range of applications of industrial and commercial significance. Binary neural networks (BNN) are particularly effective in trading accuracy for performance, energy efficiency or hardware/software complexity. Here, we introduce a spintronic, re-configurable in-memory BNN accelerator, PIMBALL: Processing In Memory BNN AcceL(L)erator, which allows for massively parallel and energy efficient computation. PIMBALL is capable of being used as a standard spintronic memory (STT-MRAM) array and a computational substrate simultaneously. We evaluate PIMBALL using multiple image classifiers and a genomics kernel. Our simulation results show that PIMBALL is more energy efficient than alternative CPU, GPU, and FPGA based implementations while delivering higher throughput.

cs.ET↗

arXiv2019

Detection of Influenza A Virus Nucleoprotein Through the Self-Assembly of Nanoparticles in Magnetic Particle Spectroscopy-Based Bioassays: A Method for Rapid, Sensitive, and Wash-free Magnetic Immunoassays

Magnetic nanoparticles (MNPs) with proper surface functionalization have been extensively applied as labels for magnetic immunoassays, carriers for controlled drug/gene delivery, tracers and contrasts for magnetic imaging, etc. Here, we introduce a new biosensing scheme based on magnetic particle spectroscopy (MPS) and the self-assembly of MNPs to quantitatively detect H1N1 nucleoprotein molecules. MPS monitors the harmonics of oscillating MNPs as a metric for the freedom of rotational motion, thus indicating the bound states of MNPs. These harmonics can be readily collected from nanogram quantities of iron oxide nanoparticles within 10 s. H1N1 nucleoprotein molecule hosts multiple different epitopes that forms binding sites for many IgG polyclonal antibodies. Anchoring IgG polyclonal antibodies onto MNPs triggers the cross-linking between MNPs and H1N1 nucleoprotein molecules, thereby forming MNP self-assemblies. Using MPS and the self-assembly of MNPs, we achieved the sensitivity of 44 nM (442 pmole) for detecting H1N1 nucleoprotein. In addition, the morphologies and the hydrodynamic sizes of the MNP self-assemblies are characterized to verify the MPS results. Different MNP self-assembly models such as classical cluster, open ring tetramer, chain model as well as multimers (from dimer to pentamer) are proposed in this paper. Herein, we claim the feasibility of using MPS and the self-assembly of MNPs as a new biosensing scheme for detecting ultralow concentrations of target biomolecules, which can be employed as rapid, sensitive, and wash-free magnetic immunoassays.

physics.app-ph↗

arXiv2019

Tunable Magnetic Domain Walls for Therapeutic Neuromodulation at Cellular Level: Stimulating Neurons Through Magnetic Nanowires

Cellular-level neuron stimulation has attracted much attention in the areas of prevention, diagnosis and treatment of neurological disorders. Herein, we propose a spintronic neurostimulator based on the domain wall movement inside stationary magnetic nanowires driven by the spin transfer torque. The electromotive forces generated by the domain wall motion can serve as highly localized stimulation signals for neuron cells. Our simulation results show that the induced electric field from the domain wall motion in permalloy nanowires can reach up to 14 V/m, which is well above the reported threshold stimulation signal for clinical applications. The proposed device operates on a current range of several uA which is 10^3 times lower compared to magnetic stimulation by microcoils. The duration and amplitude of the stimulating signal can be controlled by adjusting the applied current density, the geometry of the nanowire, and the magnetic properties of the nanowire material.

physics.med-ph↗

arXiv2019

Deterministic Field-free Switching of a Perpendicularly Magnetized Ferromagnetic Layer via the Joint Effects of Dzyaloshinskii-Moriya Interaction and Field-like Spin-orbit Torque: An Appraisal

Field-free switching of perpendicularly magnetized ferromagnetic layer by spin orbit torque (SOT) from the spin Hall effect (SHE) is of great interest in the applications of magnetic memory devices. In this paper, we investigate the deterministic SOT switching through the joint effects of Dzyaloshinskii-Moriya Interaction (DMI) and field-like torque (FLT) by micromagnetic simulations. We confirmed that within a certain range of DMI values and charge current densities, it is possible to deterministically switch the magnetization without the assistance external magnetic field. We show that the FLT could play an adverse role in blocking and slowing down the magnetization switching under certain cases of DMI and charge current-driven field-free switching. However, in other cases, FLT can assist DMI on the deterministic field-free SOT switching. In addition, it is found that FLT can effectively expand the current density window for a deterministic field-free SOT switching in the presence of DMI.

physics.app-ph↗

arXiv2019

Spin-orbit Torque and Spin Hall Effect-based Cellular Level Therapeutic Neuromodulators: Modulating Neuron Activities through Spintronic Nanodevices

Artificial modulation of a neuronal subset through ion channels activation can initiate firing patterns of an entire neural circuit in vivo. As nanovalves in the cell membrane, voltage-gated ion channels can be artificially controlled by the electric field gradient that caused by externally applied time varying magnetic fields. Herein, we theoretically investigate the feasibility of modulating neural activities by using magnetic spintronic nanostructures. An antiferromagnet/ferromagnet (AFM/FM) structure is explored as neuromodulator. For FM layer with perpendicular magnetization, stable bidirectional magnetization switching can be achieved by applying in-plane currents through AFM layer to induce the spin-orbit torque (SOT) due to the spin Hall effect (SHE). This Spin-orbit Torque Neurostimulator (SOTNS) utilizes in-plane charge current pulses to switch the magnetization in FM layer. The time changing magnetic stray field induces electric field that modulates the surrounding neurons. The Object Oriented Micromagnetic Framework (OOMMF) is used to calculate space and time dependent magnetic dynamics of SOTNS structure. The current driven magnetization dynamics in SOTNS has no mechanically moving parts. Furthermore, the size of SOTNS can be down to tens of nanometers, thus, arrays of SOTNSs could be fabricated, integrated together and patterned on a flexible substrate, which gives us much more flexible control of the neuromodulation with cellular resolution.

physics.app-ph↗

arXiv2019

Investigating the Effect of Magnetic Dipole-Dipole Interaction on Magnetic Particle Spectroscopy (MPS): Implications for Magnetic Nanoparticle-based Bioassays and Magnetic Particle Imaging (MPI)

Superparamagnetic iron oxide nanoparticles (SPIONs), with comparable size to biomolecules (such as proteins, nucleic acids, etc.) and unique magnetic properties, good biocompatibility, low toxicity, potent catalytic behavior, are promising candidates for many biomedical applications. There is one property present in most SPION systems, yet it has not been fully exploited, which is the dipole-dipole interaction (also called dipolar interaction) between the SPIONs. It is known that the magnetic dynamics of an ensemble of SPIONs are substantially influenced by the dipolar interactions. However, the exact way it affects the performance of magnetic particle-based bioassays and magnetic particle imaging (MPI) is still an open question. The purpose of this paper is to give a partial answer to this question. This is accomplished by numerical simulations on the dipolar interactions between two nearby SPIONs and experimental measurements on an ensemble of SPIONs using our lab-based magnetic particle spectroscopy (MPS) system. Our results show that even moderate changes in the SPION concentration may have substantial effects on the magnetic dynamics of the SPION system and the harmonic signal magnitudes can be increased or decreased by 60%, depending on the values of MPS system parameters.

physics.app-ph↗

arXiv2019

Tunable Magnetic Skyrmions in Ultrathin Magnetic Nanostructures for Cellular-Level Neurostimulation

In 2016, the Global Burden of Disease reported that neurological disorders were the principal cause of disability-adjusted life years (DALYs) and the second leading cause of deaths. Research in the last decade has pushed neuroscience to design and implement low-cost, efficient, implantable, flexible electrodes/probes and 3D arrays for neuron stimulation and sensing. Electrical arrays used in current CMOS-based technologies can be affected by the migration of cells (such as astrocytes) that attempt to seal off the electronic devices, causing increased impedance and alternations in the electric field. In this regard, magnetic nanodevices can be better candidates. A wide assortment of magnetic skyrmion-based device ideas and models have as of late been proposed featuring their potential applications. In this paper we propose a highly tunable skyrmion-based spintronic nanodevice for neuron stimulation. The effects of tunable material and magnetic properties specifically Dzyaloshinskii-Moriya interaction (DMI), perpendicular magnetic anisotropy (PMA) constant, number of skyrmions and device dimensions on stable skyrmion nucleation and smooth skyrmion dynamics in a magnetic ultra-thin film have been extensively studied. The aim of this study was to meet the standard therapeutic specifications of neuron stimulation, which is an electric field of about 10 mV/mm for a duration of 50 μs. From Faraday's Laws of Induction, skyrmion dynamics that generates an alternating magnetic flux density induces an electric field for a certain time duration in the ultra-thin film. The results of this work show that on tuning the skyrmion dynamics, the induced electric field can reach the standard value required for neurostimulation, thereby providing a strong futuristic possibility to exploit skyrmion-based spintronic nanodevices for neuron stimulation.

physics.app-ph↗

arXiv2018

Computational RAM to Accelerate String Matching at Scale

Traditional Von Neumann computing is falling apart in the era of exploding data volumes as the overhead of data transfer becomes forbidding. Instead, it is more energy-efficient to fuse compute capability with memory where the data reside. This is particularly critical for pattern matching, a key computational step in large-scale data analytics, which involves repetitive search over very large databases residing in memory. Emerging spintronic technologies show remarkable versatility for the tight integration of logic and memory. In this paper, we introduce CRAM-PM, a novel high-density, reconfigurable spintronic in-memory compute substrate for pattern matching.

cs.AR↗

arXiv2018

SkyLogic - A proposal for a skyrmion logic device

This work proposes a novel logic device (SkyLogic) based on skyrmions, which are magnetic vortex-like structures that have low depinning current density and are robust to defects. A charge current sent through a polarizer ferromagnet (P-FM) nucleates a skyrmion at the input end of an intra-gate FM interconnect with perpendicular magnetic anisotropy (PMA-FM). The output end of the PMA--FM forms the free layer of an MTJ stack. A spin Hall metal (SHM) is placed beneath the PMA-FM. The skyrmion is propagated to the output end of the PMA-FM by passing a charge current through the SHM. The resistance of the MTJ stack is low (high) when a skyrmion is present (absent) in the free layer, thereby realizing an inverter. A framework is developed to analyze the performance of the SkyLogic device. A circuit-level technique is developed that counters the transverse displacement of skyrmion in the PMA-FM and allows use of high current densities for fast propagation. The design space exploration of the PMA-FM material parameters is performed to obtain an optimal design point. At the optimal point, we obtain an inverter delay of 434 ps with a switching energy of 7.1 fJ.

cs.ET↗

arXiv2018

Magnetic Nanoparticles in Nanomedicine

Nanomaterials, in addition to their small size, possess unique physicochemical properties that differ from the bulk materials, making them ideal for a host of novel applications. Magnetic nanoparticle (MNP) is one important class of nanomaterials that have been widely studied for their potential applications in nanomedicine. Due to the fact that MNPs can be detected and manipulated by remote magnetic fields, it opens a wide opportunity for them to be used in vivo. Nowadays, MNPs have been used for diverse applications including magnetic biosensing (diagnostics), magnetic imaging, magnetic separation, drug and gene delivery, and hyperthermia therapy, etc. This review aims to provide a comprehensive assessment of the state-of-the-art biological and biomedical applications of MNPs. In addition, the development of high magnetic moment MNPs with proper surface functionalization has progressed exponentially over the past decade. Herein, we also reviewed the recent advances in the synthesis and surface coating strategies of MNPs. This review is not only to provide in-depth insights into the different synthesis, biofunctionalization, biosensing, imaging, and therapy methods but also to give an overview of limitations and possibilities of each technology.

physics.app-ph↗

arXiv2018

Large-scale defects hidden inside a topological insulator grown onto a 2D substrate

Topological insulator (TI) materials are exciting candidates for integration into next-generation memory and logic devices because of their potential for efficient, low-energy-consumption switching of magnetization. Specifically, the family of bismuth chalcogenides offers efficient spin-to-charge conversion because of its large spin-orbit coupling and spin-momentum locking of surface states. However, a major obstacle to realizing the promise of TIs is the thin-film materials' quality, which lags behind that of epitaxially grown semiconductors. In contrast to the latter systems, the Bi-chalcogenides form by van der Waals epitaxy, which allows them to successfully grow onto substrates with various degrees of lattice mismatch. This flexibility enables the integration of TIs into heterostructures with emerging materials, including two-dimensional materials. However, understanding and controlling local features and defects within the TI films is critical to achieving breakthrough device performance. Here, we report observations and modeling of large-scale structural defects in (Bi,Sb)$_2$Te$_3$ films grown onto hexagonal BN, highlighting unexpected symmetry-breaking rotations within the films and the coexistence of a second phase along grain boundaries. Using first-principles calculations, we show that these defects could have consequential impacts on the devices that rely on these TI films, and therefore they cannot be ignored.

cond-mat.mtrl-sci↗

arXiv2018

Large unidirectional spin Hall and Rashba-Edelstein magnetoresistance in topological insulator/magnetic insulator heterostructures

Thanks to its unique symmetry, the unidirectional spin Hall and Rashba-Edelstein magnetoresistance (USRMR) is of great fundamental and practical interest, particularly in the context of reading magnetization states in two-terminal spin-orbit torque switching memory and logic devices. Recent studies show that topological insulators could improve USRMR amplitude. However, the topological insulator device configurations studied so far in this context, namely ferromagnetic metal/topological insulator bilayers and magnetically doped topological insulators, suffer from current shunting by the metallic layer and low Curie temperature, respectively. Here, we report large USRMR in a new material category - magnetic insulator/topological insulator bi-layered heterostructures. Such structures exhibit USRMR that is about an order of magnitude larger than the highest values reported so far in all-metal Ta/Co bilayers. We also demonstrate current-induced magnetization switching aided by an Oersted field, and electrical read out by the USRMR, as a prototype memory device.

cond-mat.mes-hall↗

arXiv2018

Field-free switching of perpendicular magnetic tunnel junction by the interplay of spin orbit and spin transfer torques

Spin-orbit torque and spin-transfer torque are leading the pathway to the future of spintronic memories. However, both of the mechanisms are suffering from intrinsic limitations. In particular, an external magnetic field is required for spin-orbit torque to execute deterministic switching in perpendicular magnetic tunnel junctions; the demand for reduced spin-transfer torque switching current to realize ultralow power is still remaining. Thus, a more advanced switching mechanism is urgently needed to move forward spintronics for wide applications. Here, we experimentally demonstrate the field-free switching of three-terminal perpendicular-anisotropy nanopillar devices through the interaction between spin-orbit and spin-transfer torques. The threshold current density of spin-transfer torque switching is reduced to 0.94 MA.cm-2, which is a significant decrease compared to that in other current-induced magnetization switching mechanisms. In addition, thanks to the interplay of spin-orbit and spin-transfer torques, lower current-induced switching in the conventional two-terminal perpendicular magnetic tunnel junctions is also achieved.

physics.app-ph↗

arXiv2018

L10 Fe-Pd Synthetic Antiferromagnet through an fcc Ru Spacer Utilized for Perpendicular Magnetic Tunnel Junctions

Magnetic materials that possess large bulk perpendicular magnetic anisotropy (PMA) are essential for the development of magnetic tunnel junctions (MTJs) used in future spintronic memory and logic devices. The addition of an antiferromagnetic layer to these MTJs was recently predicted to facilitate ultra-fast magnetization switching. Here, we report a demonstration of a bulk perpendicular synthetic antiferromagnetic (P-SAFM) structure comprised of a (001) textured FePd/Ru/FePd trilayer with a face-centered-cubic (fcc) phase Ru spacer. The L10 FePd P-SAFM structure shows a large bulk PMA (~10.2 Merg/cc) and strong antiferromagnetic coupling (~2.60 erg/cm2). Full perpendicular magnetic tunnel junctions (P-MTJs) with a L10 FePd P-SAFM layer are then fabricated. Tunneling magnetoresistance ratios of up to ~25% (~60%) are observed at room temperature (5K) after post-annealing at 350 C. Exhibiting high thermal stabilities and large Ku, the bulk P-MTJs with an L10 FePd P-SAFM layer could pave a way for next-generation ultrahigh-density and ultra-low-energy spintronic applications.

cond-mat.mtrl-sci↗

arXiv2018

Optimization of Time-Resolved Magneto-optical Kerr Effect Signals for Magnetization Dynamics Measurements

Recently magnetic storage and magnetic memory have shifted towards the use of magnetic thin films with perpendicular magnetic anisotropy (PMA). Understanding the magnetic damping in these materials is crucial, but normal Ferromagnetic Resonance (FMR) measurements face some limitations. The desire to quantify the damping in materials with PMA has resulted in the adoption of Time-Resolved Magneto-optical Kerr Effect (TR-MOKE) measurements. In this paper, we discuss the angle and field dependent signals in TR-MOKE, and utilize a numerical algorithm based on the Landau-Lifshitz-Gilbert (LLG) equation to provide information on the optimal conditions to run TR-MOKE measurements.

cond-mat.mes-hall↗

arXiv2017

External-Field-Free Spin Hall Switching of Perpendicular Magnetic Nanopillar with a Dipole-Coupled Composite Structure

Spin Hall effect (SHE) induced reversal of perpendicular magnetization has attracted significant interest, due to its potential to lead to low power memory and logic devices. However, the switching requires an assisted in-plane magnetic field, which hampers its practical applications. Here, we introduce a novel approach for external-field-free spin Hall switching of a perpendicular nanomagnet by utilizing a local dipolar field arising from an adjacent in-plane magnetic layer. Robust switching of perpendicular CoFeB nanopillars in a dipole-coupled composite stack is experimentally demonstrated in the absence of any external magnetic field, in consistent with the results of micromagnetic simulation. Large in-plane compensation field of about 135 Oe and out-of-plane loop shift of about 45 Oe / 10 7 A cm-2 are obtained in the nanopillar devices with composite structure. By performing micromagnetic simulations, we confirm the composite external-field-free switching strategy can also work for a 10 x 10 nm2 circular pillar. Compared with other proposed methods for external-field-free spin Hall switching of perpendicular magnetization, the dipole-coupled composite structure is compatible with a wide range of spin Hall systems and perpendicular magnetic tunnel junctions, paving the way towards practical SHE-based MRAM and logic applications.

cond-mat.mtrl-sci↗