arXiv subjects

J. Du

Publications and source records attributed to J. Du.

12 recordsLinked to original sources

arXiv2017

Electric field Control of Exchange Bias by Resistive Switching

We demonstrated an electric field controlled exchange bias (EB) effect accompanied with unipolar resistive switching behavior in the Si/SiO2/Pt/Co/NiO/Pt device. By applying certain voltages, the device displays obvious EB in high-resistance-state while negligible EB in low-resistance-state. Conductive filaments forming and rupture in the NiO layer but near the Co-NiO interface are considered to play dominant roles in determining the combined resistive switching and EB phenomena. This work paves a new way for designing multifunctional and nonvolatile magnetic-electrical random access memory devices.

cond-mat.mtrl-sci↗

arXiv2017

Multiband NFC for High-Throughput Wireless Computer Vision Sensor Network

Vision sensors lie in the heart of computer vision. In many computer vision applications, such as AR/VR, non-contacting near-field communication (NFC) with high throughput is required to transfer information to algorithms. In this work, we proposed a novel NFC system which utilizes multiple frequency bands to achieve high throughput.

cs.NI↗

arXiv2017

Thermal vacancy formation energies of random solid solutions

Vacancy mechanism plays a dominant role in the atomic migration when a close-packed disordered alloy undergoes ordering transition. However, the calculation of thermal vacancy formation energies (VFEs) of random solid solutions is usually cumbersome due to the difficulty in considering various local atomic environments. Here, we propose a transparent way that combines coherent potential approximation and supercell-local cluster expansion to investigate VFEs of random solid solutions. This method is used to study the effects of temperature, strain and magnetism on the VFEs of random A1-FePt alloy. The results show that the mean VFE increases with increasing temperature, decreases under (001) in-plane tensile and compressive strains, and can be further reduced by the magnetic excitation. These effects are explained by discussing the dependence of VFE on local atomic environments and the overall bond strength within.

cond-mat.mtrl-sci↗

arXiv2017

An integrated device with high performance multi-function generators and Time-to-digital convertors

A highly integrated, high performance, and re-configurable device, which is designed for the Nitrogen-Vacancy center based quantum applications, is reported. The digital compartment of the device is fully implemented in a Field-Programmable-Gate- Array. The digital compartment is designed to manage the multi-function digital waveform generation and the Time-to-Digital-Convertors. The device provides two Arbitrary-Waveform-Generator channels which operate at a 1 Gsps sampling rate with a maximum bandwidth of 500 MHz. There are twelve pulse channels integrated in the device with a 50 ps time resolution in both duration and delay. The pulse channels operate with the 3.3 V Transistor-Transistor logic. The FPGA-based Timeto- Digital-Convertor provides a 23-ps time measurement precision. A data accumulation module, which can record the input count rate and the distributions of the time measurement, is also available. A Digital-to-Analog-Convertor board is implemented as the analog compartment, which converts the digital waveforms to analog signals with 500 MHz low-pass-filters. All the input and output channels of the device are equipped with 50 Sub-Miniature version A termination. The hardware design is modularized thus it can be easily upgraded with compatible components. The device is suitable to be applied in the quantum technologies based on the N-V centers, as well as in other quantum solid state systems, such as quantum dots, phosphorus doped in silicon and defect spins in silicon carbide.

physics.ins-det↗

arXiv2015

Asymptotic properties of multivariate tapering for estimation and prediction

Parameter estimation for and prediction of spatially or spatio--temporally correlated random processes are used in many areas and often require the solution of a large linear system based on the covariance matrix of the observations. In recent years, the dataset sizes to which these methods are applied have steadily increased such that straightforward statistical tools are computationally too expensive to be used. In the univariate context, tapering, i.e., creating sparse approximate linear systems, has been shown to be an efficient tool in both the estimation and prediction settings. The asymptotic properties are derived under an infill asymptotic setting. In this paper we use a domain increasing framework for estimation and prediction using multivariate tapering. Under this asymptotic regime we prove that tapering (one-tapered form) preserves the consistency of the untapered maximum likelihood estimator and show that tapering has asymptotically the same mean squared prediction error as using the corresponding untapered predictor. The theoretical results are illustrated with simulations.

math.ST↗

arXiv2015

Spin and orbital moments of nanoscale Fe3O4 epitaxial thin film on MgO/GaAs(100)

Nanoscale Fe3O4 epitaxial thin film has been synthesized on MgO/GaAs(100) spintronic heterostructure, and studied with X-ray magnetic circular dichroism (XMCD). We have observed a total magnetic moment of (3.32 +- 0.1) uB/f.u., retaining 83% of the bulk value. Unquenched orbital moment of (0.47 +- 0.05) uB/f.u. has been confirmed by carefully applying the sum rule. The results offer direct experimental evidence of the bulk-like total magnetic moment and a large orbital moment in the nanoscale fully epitaxial Fe3O4/MgO/GaAs(100) heterostructure, which is significant for spintronics applications.

cond-mat.mtrl-sci↗

arXiv2012

Spin Hall Angle Quantification from Spin Pumping and Microwave Photoresistance

We present a method to quantify the spin Hall angle (SHA) with spin pumping and microwave photoresistance measurements. With this method, we separate the inverse spin Hall effect (ISHE) from other unwanted effects for permalloy/Pt bilayers using out-of-plane microwave excitation. Through microwave photoresistance measurements, the in- and out-of-plane precessing angles of the magnetization are determined and enabled for the exact determination of the injected pure spin current. This method is demonstrated with an almost perfect Lorentz line-shape for the obtained ISHE signal and the frequency independent SHA value as predicted by theory. By varying the Pt thickness, the SHA and spin-diffusion length of Pt is quantified as 0.012 (0.001) and 8.3 (0.9) nm, respectively.

cond-mat.mes-hall↗

arXiv2010

Non-monotonic variation of anomalous Hall effect with spin orbit coupling strength

For L1(0) FePt films, the anomalous Hall resistivity is found to be proportional to spontaneous magnetization $M_{\mathrm{S}}$. After the $M_{\mathrm{S}}$ temperature effect is eliminated, $ρ_{\mathrm{xyo}}$ can be fitted by $ρ_{\mathrm{xyo}}=a_{\mathrm{o}}ρ_{\mathrm{xx}}+ b_{\mathrm{o}}ρ_{\mathrm{xx}}^{\mathrm{2}}$. $a_{\mathrm{o}}$ and $b_{\mathrm{o}}$ change non-monotonically with chemical long range ordering degree $S$. Accordingly, it is indicated that for L1(0) FePt films the spin orbit coupling strength increases monotonically with increasing $S$.

cond-mat.mtrl-sci↗

arXiv2009

Improved time-resolved magneto-optical Kerr effect technique and dynamic magnetization reversal mechanism of perpendicularly magnetized $L1_{\mathrm{0}}$ FePt films

The dynamic coercivity cannot be measured rigorously by the conventional time-resolved magneto-optical Kerr effect technique because the irreversible deviation of the transient magnetization is accumulated. In order to remove the accumulation effect, the alternating magnetic field is employed and synchronized with the femtosecond laser pulse. Since the sample is reset before each single laser pulse, the accumulation effect of the irreversible deviation of the transient magnetization is removed. For perpendicularly magnetized $L1_{\mathrm{0}}$ FePt films, the dynamic magnetization reversal process is accomplished by the nucleation of reversed domains and the pinned domain wall motion.

cond-mat.str-el↗

arXiv2007

Rotation of easy axis in training effect and recovery of exchange bias in ferromagnet/antiferromagnet bilayers

For ferromagnet/antiferromagnet bilayers, rotation of the easy axis has been \textit{for the first time} observed during measurements of training effect and the recovery of exchange bias using FeNi/FeMn system. These salient phenomena strongly suggest irreversible motion of antiferromagnet spins during subsequent measurements of hysteresis loops. It is found that the rotation of the easy axis can partly account for the training effect and the recovery of the exchange bias.

cond-mat.mtrl-sci↗

arXiv2005

Experimental implementation of high-fidelity unconventional geometric quantum gates using NMR interferometer

Following a key idea of unconventional geometric quantum computation developed earlier [Phys. Rev. Lett. 91, 197902 (2003)], here we propose a more general scheme in such an intriguing way: $γ_{d}=α_{g}+ηγ_{g}$, where $γ_{d}$ and $γ_{g}$ are respectively the dynamic and geometric phases accumulated in the quantum gate operation, with $η$ as a constant and $α_{g}$ being dependent only on the geometric feature of the operation. More arrestingly, we demonstrate the first experiment to implement a universal set of such kind of generalized unconventional geometric quantum gates with high fidelity in an NMR system.

quant-ph↗

arXiv1999

Specht Modules and Branching Rules for Ariki-Koike Algebras

Specht modules for an Ariki-Koike algebra have been investigated recently in the context of cellular algebras. Thus, these modules are defined as quotient modules of certain ``permutation'' modules, that is, defined as ``cell modules'' via cellular bases. We shall introduce in this paper Specht modules for an Ariki-Koike algebra as submodules of those ``permutation'' modules and investigate their basic properties such as Standard Basis Theorem and the ordinary Branching Theorem, generalizing several classical constructions for type $A$. The second part of the paper moves on looking for Kleshchev's branching rules for Specht and irreducible modules over an Ariki-Koike algebra. We shall restrict to the case where the Ariki-Koike algebra has a semi-simple bottom. With a recent work of Ariki on the classification of irreducible modules, we conjecture that the results should be true in general if $l$-regular multipartitions are replaced by Kleshchev's multipartitions. We point out that our approach is independent of the use of cellular bases.

math.QA↗