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2010-09-29
Acoustically driven ferromagnetic resonance
Surface acoustic waves (SAW) in the GHz frequency range are exploited for the all-elastic excitation and detection of ferromagnetic resonance (FMR) in a ferromagnetic/ferroelectric (nickel/lithium niobate) hybrid device. We measure the SAW magneto-transmission at room temperature as a function of frequency, external ma...
1009.5798v2
2010-10-05
Effects of Strong Gravitational Lensing on Millimeter-Wave Galaxy Number Counts
We study the effects of strong lensing on the observed number counts of mm sources using a ray tracing simulation and two number count models of unlensed sources. We employ a quantitative treatment of maximum attainable magnification factor depending on the physical size of the sources, also accounting for effects of l...
1010.0998v2
2010-10-15
The Significance of Non-ergodicity Property of Statistical Mechanics Systems for Understanding Resting State of a Living Cell
A better grasp of the physical foundations of life is necessary before we can understand the processes occurring inside a living cell. In his physical theory of the cell, American physiologist Gilbert Ling introduced an important notion of the resting state of the cell. He describes this state as an independent stable ...
1010.3226v1
2010-11-29
Superoperator Analysis of Entanglement in a Four-Qubit Cluster State
In this paper we utilize superoperator formalism to explore the entanglement evolution of four-qubit cluster states in a number of decohering environments. A four-qubit cluster state is a resource for the performance of an arbitrary single logical qubit rotation via measurement based cluster state quantum computation. ...
1011.6336v2
2011-02-14
Computing the Ball Size of Frequency Permutations under Chebyshev Distance
Let $S_n^\lambda$ be the set of all permutations over the multiset $\{\overbrace{1,...,1}^{\lambda},...,\overbrace{m,...,m}^\lambda\}$ where $n=m\lambda$. A frequency permutation array (FPA) of minimum distance $d$ is a subset of $S_n^\lambda$ in which every two elements have distance at least $d$. FPAs have many appli...
1102.2799v2
2011-02-25
Modeling Extragalactic Foregrounds and Secondaries for Unbiased Estimation of Cosmological Parameters From Primary CMB Anisotropy
Using the latest physical modeling and constrained by the most recent data, we develop a phenomenological parameterized model of the contributions to intensity and polarization maps at millimeter wavelengths from external galaxies and Sunyaev-Zeldovich effects. We find such modeling to be necessary for estimation of co...
1102.5195v1
2011-03-02
Switching dynamics of a magnetostrictive single-domain nanomagnet subjected to stress
The temporal evolution of the magnetization vector of a single-domain magnetostrictive nanomagnet, subjected to in-plane stress, is studied by solving the Landau-Lifshitz-Gilbert equation. The stress is ramped up linearly in time and the switching delay, which is the time it takes for the magnetization to flip, is comp...
1103.0352v1
2011-03-21
Delay Constrained Throughput Analysis of a Correlated MIMO Wireless Channel
The maximum traffic arrival rate at the network for a given delay guarantee (delay constrained throughput) has been well studied for wired channels. However, few results are available for wireless channels, especially when multiple antennas are employed at the transmitter and receiver. In this work, we analyze the netw...
1103.4016v1
2011-03-29
Current induced rotational torques in the skyrmion lattice phase of chiral magnets
In chiral magnets without inversion symmetry, the magnetic structure can form a lattice of magnetic whirl lines, a two-dimensional skyrmion lattice, stabilized by spin-orbit interactions in a small range of temperatures and magnetic fields. The twist of the magnetization within this phase gives rise to an efficient cou...
1103.5548v2
2011-04-07
Finite-size effects on the magnetoelectric response of field-driven ferroelectric/ferromagnetic chains
We study theoretically the coupled multiferroic dynamics of one-dimensional ferroelectric/ferromagnet chains driven by harmonic magnetic and electric fields as a function of the chain length. A linear magnetoelectric coupling is dominated by the spin-polarized screening charge at the interface. We performed Monte-Carlo...
1104.1269v3
2011-04-12
The Effect of Disorder in Superfluid Double Layer Graphene
We investigate the superfluid properties of disordered double layer graphene systems using the non-equilibrium Green's function (NEGF) formalism. The complexity of such a structure makes it imperative to study the effects of lattice vacancies which will inevitably arise during fabrication. We present and compare room t...
1104.2343v1
2011-05-12
Incremental Cycle Detection, Topological Ordering, and Strong Component Maintenance
We present two on-line algorithms for maintaining a topological order of a directed $n$-vertex acyclic graph as arcs are added, and detecting a cycle when one is created. Our first algorithm handles $m$ arc additions in $O(m^{3/2})$ time. For sparse graphs ($m/n = O(1)$), this bound improves the best previous bound by ...
1105.2397v1
2011-05-30
Orthogonal Matching Pursuit: A Brownian Motion Analysis
A well-known analysis of Tropp and Gilbert shows that orthogonal matching pursuit (OMP) can recover a k-sparse n-dimensional real vector from 4 k log(n) noise-free linear measurements obtained through a random Gaussian measurement matrix with a probability that approaches one as n approaches infinity. This work strengt...
1105.5853v1
2011-06-07
Magneto-optical Kerr Effect Studies of Square Artificial Spin Ice
We report a magneto-optical Kerr effect study of the collective magnetic response of artificial square spin ice, a lithographically-defined array of single-domain ferromagnetic islands. We find that the anisotropic inter-island interactions lead to a non-monotonic angular dependence of the array coercive field. Compari...
1106.1394v2
2011-06-15
Dissipative hydrodynamic equation of a ferromagnetic Bose-Einstein condensate: Analogy to magnetization dynamics in conducting ferromagnets
The hydrodynamic equation of a spinor Bose-Einstein condensate (BEC) gives a simple description of spin dynamics in the condensate. We introduce the hydrodynamic equation of a ferromagnetic BEC with dissipation originating from the energy dissipation of the condensate. The dissipative hydrodynamic equation has the same...
1106.2876v4
2011-07-02
Energy dissipation and switching delay in spin-transfer torque switching of nanomagnets with low-saturation magnetization in the presence of thermal fluctuations
A common ploy to reduce the switching current and energy dissipation in spin-transfer-torque driven magnetization switching of shape-anisotropic single-domain nanomagnets is to employ magnets with low saturation magnetization $M_s$ and high shape-anisotropy. The high shape-anisotropy compensates for low $M_s$ to keep t...
1107.0387v2
2011-08-01
Noise Sensitivity in Continuum Percolation
We prove that the Poisson Boolean model, also known as the Gilbert disc model, is noise sensitive at criticality. This is the first such result for a Continuum Percolation model, and the first for which the critical probability p_c \ne 1/2. Our proof uses a version of the Benjamini-Kalai-Schramm Theorem for biased prod...
1108.0310v2
2011-08-23
Vortex Lines in Topological Insulator-Superconductor Heterostructures
3D topological insulator/s-wave superconductor heterostructures have been predicted as candidate systems for the observation of Majorana fermions in the presence of superconducting vortices. In these systems, Majorana fermions are expected to form at the interface between the topological insulator and the superconducto...
1108.4711v1
2011-08-28
Low-complexity quantum codes designed via codeword-stabilized framework
We consider design of the quantum stabilizer codes via a two-step, low-complexity approach based on the framework of codeword-stabilized (CWS) codes. In this framework, each quantum CWS code can be specified by a graph and a binary code. For codes that can be obtained from a given graph, we give several upper bounds on...
1108.5490v1
2011-09-16
Parallel Sparse Matrix-Matrix Multiplication and Indexing: Implementation and Experiments
Generalized sparse matrix-matrix multiplication (or SpGEMM) is a key primitive for many high performance graph algorithms as well as for some linear solvers, such as algebraic multigrid. Here we show that SpGEMM also yields efficient algorithms for general sparse-matrix indexing in distributed memory, provided that the...
1109.3739v2
2011-10-06
A new class of codes for Boolean masking of cryptographic computations
We introduce a new class of rate one-half binary codes: {\bf complementary information set codes.} A binary linear code of length $2n$ and dimension $n$ is called a complementary information set code (CIS code for short) if it has two disjoint information sets. This class of codes contains self-dual codes as a subclass...
1110.1193v2
2011-10-31
Calculation of coercivity of magnetic nanostructures at finite temperatures
We report a finite temperature micromagnetic method (FTM) that allows for the calculation of the coercive field of arbitrary shaped magnetic nanostructures at time scales of nanoseconds to years. Instead of directly solving the Landau-Lifshitz-Gilbert equation, the coercive field is obtained without any free parameter ...
1110.6789v1
2011-11-10
Magnetic friction: From Stokes to Coulomb behavior
We demonstrate that in a ferromagnetic substrate, which is continuously driven out of equilibrium by a field moving with constant velocity $v$, at least two types of friction may occur when $v$ goes to zero: The substrate may feel a friction force proportional to $v$ (Stokes friction), if the field changes on a time sc...
1111.2494v1
2011-11-15
Revisiting No-Scale Supergravity Inspired Scenarios
We consider no-scale supergravity inspired scenarios, emphasizing the possible dynamical determination of the soft supersymmetry-breaking parameters as triggered by the radiative corrections that lift an essentially flat tree-level potential in the hidden sector. We (re)emphasize the important role played by the scale-...
1111.3455v1
2011-11-24
Spin-Wave Modes and Their Intense Excitation Effects in Skyrmion Crystals
We theoretically study spin-wave modes and their intense excitations activated by microwave magnetic fields in the skyrmion-crystal phase of insulating magnets by numerically analyzing a two-dimensional spin model using the Landau-Lifshitz-Gilbert equation. Two peaks of spin-wave resonances with frequencies of ~1 GHz a...
1111.5667v1
2011-11-26
Energy dissipation and switching delay in stress-induced switching of multiferroic devices in the presence of thermal fluctuations
Switching the magnetization of a shape-anisotropic 2-phase multiferroic nanomagnet with voltage-generated stress is known to dissipate very little energy ($<$ 1 aJ for a switching time of $\sim$0.5 ns) at 0 K temperature. Here, we show by solving the stochastic Landau-Lifshitz-Gilbert equation that switching can be car...
1111.6129v1
2011-11-30
Multi-Weyl Topological Semimetals Stabilized by Point Group Symmetry
We perform a complete classification of two-band $\bk\cdot\mathbf{p}$ theories at band crossing points in 3D semimetals with $n$-fold rotation symmetry and broken time-reversal symmetry. Using this classification, we show the existence of new 3D topological semimetals characterized by $C_{4,6}$-protected double-Weyl no...
1111.7309v2
2011-12-01
Gate controlled Spin-Density Wave and Chiral FFLO Superconducting phases in interacting Quantum Spin Hall edge states
We explore the phases exhibited by an interacting quantum spin Hall edge state in the presence of finite chemical potential (applied gate voltage) and spin imbalance (applied magnetic field). We find that the helical nature of the edge state gives rise to orders that are expected to be absent in non-chiral one-dimensio...
1112.0289v1
2011-12-04
A New Approach to Incremental Cycle Detection and Related Problems
We consider the problem of detecting a cycle in a directed graph that grows by arc insertions, and the related problems of maintaining a topological order and the strong components of such a graph. For these problems, we give two algorithms, one suited to sparse graphs, and the other to dense graphs. The former takes t...
1112.0784v1
2011-12-05
Vortex core magnetization dynamics induced by thermal excitation
We investigate the effect of temperature on the dynamic properties of magnetic vortices in small disks. Our calculations use a stochastic version of the Landau-Lifshitz-Gilbert (LLG) equation, valid for finite temperatures well below the Curie critical temperature. We show that a finite temperature induces a vortex pre...
1112.0911v2
2011-12-08
A 2-20 GHz Analog Lag-Correlator for Radio Interferometry
We present the design and testing of a 2-20 GHz continuum band analog lag correlator with 16 frequency channels for astronomical interferometry. The correlator has been designed for future use with a prototype single-baseline interferometer operating at 185-275 GHz. The design uses a broadband Wilkinson divider tree wi...
1112.1982v1
2011-12-12
An analysis of constraints on relativistic species from primordial nucleosynthesis and the cosmic microwave background
We present constraints on the number of relativistic species from a joint analysis of cosmic microwave background (CMB) fluctuations and light element abundances (helium and deuterium) compared to big bang nucleosynthesis (BBN) predictions. Our BBN calculations include updates of nuclear rates in light of recent experi...
1112.2683v1
2011-12-22
Higgs boson decay into 2 photons in the type~II Seesaw Model
We study the two photon decay channel of the Standard Model-like component of the CP-even Higgs bosons present in the type II Seesaw Model. The corresponding cross-section is found to be significantly enhanced in parts of the parameter space, due to the (doubly-)charged Higgs bosons' $(H^{\pm \pm})H^\pm$ virtual contri...
1112.5453v1
2012-01-18
Cavity approach to sphere packing in Hamming space
In this paper we study the hard sphere packing problem in the Hamming space by the cavity method. We show that both the replica symmetric and the replica symmetry breaking approximations give maximum rates of packing that are asymptotically the same as the lower bound of Gilbert and Varshamov. Consistently with known n...
1201.3863v2
2012-01-19
Impact of microstructure, temperature and strain ratio on energy-based low- cycle fatigue life prediction models for TiAl alloys
In this paper, two fatigue lifetime prediction models are tested on TiAl intermetallic using results from uniaxial low-cycle fatigue tests. Both assessments are based on dissipated energy but one of them considers a hydrostatic pressure correction. This work allows to confirm, on this kind of material, the linear natur...
1201.4084v1
2012-01-23
Influence of the magnetoelectric coupling on the electric field induced magnetization reversal in a composite non-strained multiferroic chain
We study theoretically the multiferroic dynamics in a composite one-dimensional system consisting of BaTiO3 multiferroically coupled to an iron chain. The method treats the magnetization and the polarization as thermodynamic quantities describable via a combination of the Landau-Lifshits- Gilbert and the Ginzburg-Landa...
1201.4740v1
2012-01-27
Domain-wall complexes in ferromagnetic stripes
Interaction of domain walls (DWs) in ferromagnetic stripes is studied with relevance to the formation of stable complexes of many domains. Two DW system is described with the Landau-Lifshitz-Gilbert equation including regimes of narrow and wide stripes which correspond the presence of transverse and vortex DWs. The DWs...
1201.5760v3
2012-01-31
Interlayer Transport in Disordered Semiconductor Electron Bilayers
We study the effects of disorder on the interlayer transport properties of disordered semiconductor bilayers outside of the quantum Hall regime by performing self-consistent quantum transport calculations. We find that the addition of material disorder to the system affects interlayer interactions leading to significan...
1202.0053v1
2012-02-01
Imaging topologically protected transport with quantum degenerate gases
Ultracold and quantum degenerate gases held near conductive surfaces can serve as sensitive, high resolution, and wide-area probes of electronic current flow. Previous work has imaged transport around grain boundaries in a gold wire by using ultracold and Bose-Einstein condensed atoms held microns from the surface with...
1202.0060v2
2012-02-02
Large deviations and transitions between equilibria for stochastic Landau-Lifshitz-Gilbert equation
We study a stochastic Landau-Lifshitz equation on a bounded interval and with finite dimensional noise. We first show that there exists a pathwise unique solution to this equation and that this solution enjoys the maximal regularity property. Next, we prove the large deviations principle for small noise asymptotic of s...
1202.0370v2
2012-02-06
Atomic level micromagnetic model of recording media switching at elevated temperatures
An atomic level micromagnetic model of granular recording media is developed and applied to examine external field-induced grain switching at elevated temperatures which captures non-uniform reversal modes. The results are compared with traditional methods which employ the Landau-Lifshitz-Gilbert equations based on uni...
1202.1131v1
2012-02-10
A model of magnetic order in hexagonal HoMnO3
Symmetry arguments are used to develop a spin Hamiltonian for the description of the complex magnetic ordering in HoMnO$_3$. Using a novel application of the Landau Lifshitz Gilbert dynamic torque equations to this model of the frustrated Mn ions on an $AB$ stacked triangular antiferromagnetic, it is shown that the fou...
1202.2321v1
2012-02-13
Switching Distributions for Perpendicular Spin-Torque Devices within the Macrospin Approximation
We model "soft" error rates for writing (WSER) and for reading (RSER) for perpendicular spin-torque memory devices by solving the Fokker-Planck equation for the probability distribution of the angle that the free layer magnetization makes with the normal to the plane of the film. We obtain: (1) an exact, closed form, a...
1202.2621v1
2012-02-13
Error- and Loss-Tolerances of Surface Codes with General Lattice Structures
We propose a family of surface codes with general lattice structures, where the error-tolerances against bit and phase errors can be controlled asymmetrically by changing the underlying lattice geometries. The surface codes on various lattices are found to be efficient in the sense that their threshold values universal...
1202.2743v1
2012-02-28
A method for exploratory repeated-measures analysis applied to a breast-cancer screening study
When a model may be fitted separately to each individual statistical unit, inspection of the point estimates may help the statistician to understand between-individual variability and to identify possible relationships. However, some information will be lost in such an approach because estimation uncertainty is disrega...
1202.6133v1
2012-03-15
Size bias and differential lensing of strongly lensed, dusty galaxies identified in wide-field surveys
We address two selection effects that operate on samples of gravitationally lensed dusty galaxies identified in millimeter- and submillimeter-wavelength surveys. First, we point out the existence of a "size bias" in such samples: due to finite source effects, sources with higher observed fluxes are increasingly biased ...
1203.3267v2
2012-03-28
Decoherence and mode-hopping in a magnetic tunnel junction-based spin-torque oscillator
We discuss the coherence of magnetic oscillations in a magnetic tunnel junction-based spin-torque oscillator as a function of external field angle. Time-frequency analysis shows mode-hopping between distinct oscillator modes, which arises from linear and nonlinear couplings in the Landau-Lifshitz-Gilbert equation, anal...
1203.6300v1
2012-04-28
Topological Excitonic Superfluids in Three Dimensions
We study the equilibrium and non-equilibrium properties of topological dipolar intersurface exciton condensates within time-reversal invariant topological insulators in three spatial dimensions without a magnetic field. We elucidate that, in order to correctly identify the proper pairing symmetry within the condensate ...
1204.6351v2
2012-05-29
Thermally-Assisted Spin-Transfer Torque Magnetization Reversal in Uniaxial Nanomagnets
We simulate the stochastic Landau-Lifshitz-Gilbert (LLG) dynamics of a uniaxial nanomagnet out to sub-millisecond timescales using a graphical processing unit based micromagnetic code and determine the effect of geometrical tilts between the spin-current and uniaxial anisotropy axes on the thermally assisted reversal d...
1205.6509v1
2012-06-06
Fractional Spin Josephson Effect and Electrically Controlled Magnetization in Quantum Spin Hall Edges
We explore a spin Josephson effect in a system of two ferromagnets coupled by a tunnel junction formed of 2D time-reversal invariant topological insulators. In analogy with the more commonly studied instance of the Josephson effect for charge in superconductors, we investigate properties of the phase-coherent {\it spin...
1206.1295v2
2012-06-07
Magnetic particle hyperthermia: Power losses under circularly polarized field in anisotropic nanoparticles
The deterministic Landau-Lifshitz-Gilbert equation has been used to investigate the nonlinear dynamics of magnetization and the specific loss power in magnetic nanoparticles with uniaxial anisotropy driven by a rotating magnetic field, generalizing the results obtained for the isotropic case found in [P. F. de Chatel, ...
1206.1544v2
2012-06-27
Searching for Fast Optical Transients using VERITAS Cherenkov Telescopes
Astronomical transients are intrinsically interesting things to study. Fast optical transients (microsecond timescale) are a largely unexplored field of optical astronomy mainly due to the fact that large optical telescopes are oversubscribed. Furthermore, most optical observations use instruments with integration time...
1206.6535v1
2012-07-05
Perpendicular Magnetization and Generic Realization of the Ising Model in Artificial Spin Ice
We have studied frustrated kagome arrays and unfrustrated honeycomb arrays of magnetostatically-interacting single-domain ferromagnetic islands with magnetization normal to the plane. The measured pairwise spin correlations of both lattices can be reproduced by models based solely on nearest-neighbor correlations. The ...
1207.1456v1
2012-07-13
Magnetic vortices induced by a moving tip
A two-dimensional easy-plane ferromagnetic substrate, interacting with a dipolar tip which is magnetised perpendicular with respect to the easy plane is studied numerically by solving the Landau-Lifshitz Gilbert equation. Due to the symmetry of the dipolar field of the tip, in addition to the collinear structure a magn...
1207.3225v2
2012-07-24
Bulk Topological Invariants in Noninteracting Point Group Symmetric Insulators
We survey various quantized bulk physical observables in two- and three-dimensional topological band insulators invariant under translational symmetry and crystallographic point group symmetries (PGS). In two-dimensional insulators, we show that: (i) the Chern number of a $C_n$-invariant insulator can be determined, up...
1207.5767v2
2012-07-30
'MOHAWK' : a 4000-fiber positioner for DESpec
We present a concept for a 4000-fibre positioner for DESpec, based on the Echidna 'tilting spine' technology. The DESpec focal plane is 450mm across and curved, and the required pitch is ~6.75mm. The size, number of fibers and curvature are all comparable with various concept studies for similar instruments already und...
1207.7011v2
2012-07-31
Throughput of Rateless Codes over Broadcast Erasure Channels
In this paper, we characterize the throughput of a broadcast network with n receivers using rateless codes with block size K. We assume that the underlying channel is a Markov modulated erasure channel that is i.i.d. across users, but can be correlated in time. We characterize the system throughput asymptotically in n....
1207.7298v1
2012-08-01
Streaming Codes for Channels with Burst and Isolated Erasures
We study low-delay error correction codes for streaming recovery over a class of packet-erasure channels that introduce both burst-erasures and isolated erasures. We propose a simple, yet effective class of codes whose parameters can be tuned to obtain a tradeoff between the capability to correct burst and isolated era...
1208.0072v1
2012-08-23
Inconsistencies in the description of pairing effects in nuclear level densities
Pairing correlations have a strong influence on nuclear level densities. Empirical descriptions and theoretical models have been developed to take these effects into account. The present article discusses cases, where descriptions of nuclear level densities are inconsistent or in conflict with the present understanding...
1208.4709v1
2012-09-26
Symmetry Protected Josephson Supercurrents in Three-Dimensional Topological Insulators
Coupling the surface state of a topological insulator (TI) to an s-wave superconductor is predicted to produce the long-sought Majorana quasiparticle excitations. However, superconductivity has not been measured in surface states when the bulk charge carriers are fully depleted, i.e., in the true topological regime tha...
1209.5830v2
2012-10-09
A microscopic model for ultrafast remagnetization dynamics
In this letter, we provide a microscopic model for the ultrafast remagnetization of atomic moments already quenched above Stoner-Curie temperature by a strong laser fluence. Combining first principles density functional theory, atomistic spin dynamics utilizing the Landau-Lifshitz-Gilbert equation and a three temperatu...
1210.2616v1
2012-10-31
Theory and Simulation of the diffusion of kinks on dislocations in bcc metals
Isolated kinks on thermally fluctuating (1/2)<111> screw, <100> edge and (1/2)<111> edge dislocations in bcc iron are simulated under zero stress conditions using molecular dynamics (MD). Kinks are seen to perform stochastic motion in a potential landscape that depends on the dislocation character and geometry, and the...
1210.8327v2
2012-11-01
Dynamically-generated pure spin current in single-layer graphene
The conductance mismatch problem limits the spin-injection efficiency significantly, and spin-injection into graphene has been usually requiring high-quality tunnel barriers to circumvent the conductance mismatch. We introduce a novel approach, which enables generation of a pure spin current into single-layer graphene ...
1211.0124v1
2012-12-04
Phenomenological theory of the giant magnetoimpedance of composite wires
Composite wires with a three-layered structure are known to show a particularly large magnetoimpedance effect. The wires consist of a highly conductive core, an insulating layer and an outer ferromagnetic shell. In order to understand the origin of the effect a theory based on a coupling of the Maxwell equations to the...
1212.0710v3
2012-12-12
Giant magnetoimpedance of composite wires with an insulation layer
Composite wires with a three-layered structure exhibit a large giant magneto-impedance (GMI) effect, which can be used in sensitive magnetic field sensors. To further investigate the origin of the GMI effect, composite wires consisting of a highly conductive copper core, a silicon dioxide layer and an outer Permalloy s...
1212.2745v2
2012-12-13
Theory of quasiparticle interference in mirror symmetric 2D systems and its application to surface states of topological crystalline insulators
We study symmetry protected features in the quasiparticle interference (QPI) pattern of 2D systems with mirror symmetries and time-reversal symmetry, around a single static point impurity. We show that, in the Fourier transformed local density of states (FT-LDOS), $\rho(\bq,\omega)$, while the position of high intensit...
1212.3285v2
2013-01-25
Chiral magnetism and helimagnons in a pyrochlore antiferromagnet
Recent neutron scattering measurements on the spinel CdCr2O4 revealed a rare example of helical magnetic order in geometrically frustrated pyrochlore antiferromagnet. The spin spiral characterized by an incommensurate wavevector Q = 2pi (0, delta, 1) with delta ~0.09 is accompanied by a tetragonal distortion. Here we c...
1301.5958v1
2013-01-31
Switching of Dipole Coupled Multiferroic Nanomagnets in the Presence of Thermal Noise: Reliability of Nanomagnetic Logic
The stress-induced switching behavior of a multiferroic nanomagnet, dipole coupled to a hard nanomagnet, is numerically studied by solving the stochastic Landau-Lifshitz-Gilbert (LLG) equation for a single domain macro-spin state. Different factors were found to affect the switching probability in the presence of therm...
1301.7490v2
2013-02-01
Vortex mechanics in planar nano-magnets
A collective-variable approach for the study of non-linear dynamics of magnetic textures in planar nano-magnets is proposed. The variables are just arbitrary parameters (complex or real) in the specified analytical function of a complex variable, describing the texture in motion. Starting with such a function, a formal...
1302.0222v3
2013-02-03
Correcting Camera Shake by Incremental Sparse Approximation
The problem of deblurring an image when the blur kernel is unknown remains challenging after decades of work. Recently there has been rapid progress on correcting irregular blur patterns caused by camera shake, but there is still much room for improvement. We propose a new blind deconvolution method using incremental s...
1302.0439v2
2013-03-01
Entropy Distance
Motivated by the approach of random linear codes, a new distance in the vector space over a finite field is defined as the logarithm of the "surface area" of a Hamming ball with radius being the corresponding Hamming distance. It is named entropy distance because of its close relation with entropy function. It is shown...
1303.0070v2
2013-03-20
On the Behavior of RObust Header Compression U-mode in Channels with Memory
The existing studies of RObust Header Compression (ROHC) have provided some understanding for memoryless channel, but the behavior of ROHC for correlated wireless channels is not well investigated in spite of its practical importance. In this paper, the dependence of ROHC against its design parameters for the Gilbert E...
1303.4970v1
2013-03-21
Tuning magnetic anisotropy in (001) oriented L10 (Fe1-xCux)55Pt45 films
We have achieved (001) oriented L10 (Fe1-xCux)55Pt45 thin films, with magnetic anisotropy up to 3.6x10^7 erg/cm^3, using atomic-scale multilayer sputtering and post annealing at 400 {\deg}C for 10 seconds. By fixing the Pt concentration, structure and magnetic properties are systematically tuned by the Cu addition. Inc...
1303.5208v1
2013-03-28
Spin Torque on Magnetic Textures Coupled to the Surface of a Three-Dimensional Topological Insulator
We investigate theoretically the spin torque and magnetization dynamic in a thin ferromagnetic (FM) layer with spatially varying magnetization. The FM layer is deposited on the surface of a topological insulator (TI). In the limit of the adiabatic relaxation of electron spin along the magnetization, the interaction bet...
1303.7031v1
2013-04-03
Synchronization of an array of spin torque nano oscillators in periodic applied external magnetic field
Considering an array of spin torque transfer nano oscillators (STNOs), we have investigated the synchronization property of the system under the action of a common periodically driven applied external magnetic field by numerically analyzing the underlying system of Landau-Lifshitz-Gilbert-Slonczewski (LLGS) equations f...
1304.0875v1
2013-04-06
Towards a living earth simulator
The Living Earth Simulator (LES) is one of the core components of the FuturICT architecture. It will work as a federation of methods, tools, techniques and facilities supporting all of the FuturICT simulation-related activities to allow and encourage interactive exploration and understanding of societal issues. Society...
1304.1903v1
2013-05-13
Backhopping effect in magnetic tunnel junctions: comparison between theory and experiment
We report on the magnetic switching and backhopping effects due to spin-transfer-torque in magnetic tunnel junctions. Experimental data on the current-induced switching in junctions with MgO tunnel barrier reveal a random back-and-forth switching between the magnetization states, which appears when the current directio...
1305.2711v1
2013-05-15
Robust Streaming Erasure Codes based on Deterministic Channel Approximations
We study near optimal error correction codes for real-time communication. In our setup the encoder must operate on an incoming source stream in a sequential manner, and the decoder must reconstruct each source packet within a fixed playback deadline of $T$ packets. The underlying channel is a packet erasure channel tha...
1305.3596v1
2013-05-16
Size-dependent magnetization switching characteristics and spin wave modes of FePt nanostructures
We present a comprehensive investigation of the size-dependent switching characteristics and spin wave modes of FePt nanoelements. Curved nanomagnets ("caps") are compared to flat disks of identical diameter and volume over a size range of 100 to 300nm. Quasi-static magnetization reversal analysis using first-order rev...
1305.3686v1
2013-05-28
Reallocation Problems in Scheduling
In traditional on-line problems, such as scheduling, requests arrive over time, demanding available resources. As each request arrives, some resources may have to be irrevocably committed to servicing that request. In many situations, however, it may be possible or even necessary to reallocate previously allocated reso...
1305.6555v1
2013-06-04
Generalized splines on arbitrary graphs
Let G be a graph whose edges are labeled by ideals of a commutative ring. We introduce a generalized spline, which is a vertex-labeling of G by elements of the ring so that the difference between the labels of any two adjacent vertices lies in the corresponding edge ideal. Generalized splines arise naturally in combina...
1306.0801v2
2013-06-04
Large Chern Number Quantum Anomalous Hall Effect In Thin-film Topological Crystalline Insulators
Quantum anomalous Hall (QAH) insulators are two-dimensional (2D) insulating states exhibiting properties similar to those of quantum Hall states but without external magnetic field. They have quantized Hall conductance $\sigma^H=Ce^2/h$, where integer $C$ is called the Chern number, and represents the number of gapless...
1306.0888v2
2013-06-07
Free energy generalization of the Peierls potential in iron
In body-centered cubic (bcc) crystals, ${1}{2}111$ screw dislocations exhibit high intrinsic lattice friction as a consequence of their non-planar core structure, which results in a periodic energy landscape known as the Peierls potential, $U_P$. The main features determining plastic flow, including its stress and temp...
1306.1633v4
2013-06-14
On a decoupled linear FEM integrator for Eddy-current-LLG
We propose a numerical integrator for the coupled system of the eddy-current equation with the nonlinear Landau-Lifshitz-Gilbert equation. The considered effective field contains a general field contribution, and we particularly cover exchange, anisotropy, applied field, and magnetic field (stemming from the eddy-curre...
1306.3319v1
2013-06-20
Lower Bounds for the Area of Black Holes in Terms of Mass, Charge, and Angular Momentum
The most general formulation of Penrose's inequality yields a lower bound for ADM mass in terms of the area, charge, and angular momentum of black holes. This inequality is in turn equivalent to an upper and lower bound for the area in terms of the remaining quantities. In this note, we establish the lower bound for a ...
1306.4739v2
2013-06-28
Coherent Nonlinear Quantum Model for Composite Fermions
Originally proposed by Read [1] and Jain [2], the so-called "composite-fermion" is a phenomenological attachment of two infinitely thin local flux quanta seen as nonlocal vortices to two-dimensional (2D) electrons embedded in a strong orthogonal magnetic field. In this letter, it is described as a highly-nonlinear and ...
1306.6869v1
2013-06-29
First-principles calculations of current-induced spin-transfer torques in magnetic domain walls
Current-induced spin-transfer torques (STTs) have been studied in Fe, Co and Ni domain walls (DWs) by the method based on the first-principles noncollinear calculations of scattering wave functions expanded in the tight-binding linearized muffin-tin orbital (TB-LMTO) basis. The results show that the out-of-plane compon...
1307.0062v1
2013-07-02
Reversal mode instability and magnetoresistance in perpendicular (Co/Pd)/Cu/(Co/Ni) pseudo-spin-valves
We have observed distinct temperature-dependent magnetization reversal modes in a perpendicular (Co/Pd)4/Co/Cu/(Co/Ni)4/Co pseudo-spin-valve, which are correlated with spin-transport properties. At 300 K, magnetization reversal occurs by vertically correlated domains. Below 200 K the hysteresis loop becomes bifurcated ...
1307.0853v1
2013-07-08
Modal Analysis with Compressive Measurements
Structural Health Monitoring (SHM) systems are critical for monitoring aging infrastructure (such as buildings or bridges) in a cost-effective manner. Such systems typically involve collections of battery-operated wireless sensors that sample vibration data over time. After the data is transmitted to a central node, mo...
1307.1960v1
2013-07-15
On the Instabilities of the Walker Propagating Domain Wall Solution
A powerful mathematical method for front instability analysis that was recently developed in the field of nonlinear dynamics is applied to the 1+1 (spatial and time) dimensional Landau-Lifshitz-Gilbert (LLG) equation. From the essential spectrum of the LLG equation, it is shown that the famous Walker rigid body propaga...
1307.3825v3
2013-07-30
Accurate Decoding of Pooled Sequenced Data Using Compressed Sensing
In order to overcome the limitations imposed by DNA barcoding when multiplexing a large number of samples in the current generation of high-throughput sequencing instruments, we have recently proposed a new protocol that leverages advances in combinatorial pooling design (group testing) doi:10.1371/journal.pcbi.1003010...
1307.7810v1
2013-08-09
Relativistic and thermal effects on the magnon spectrum of a ferromagnetic monolayer
A spin model including magnetic anisotropy terms and Dzyaloshinsky-Moriya interactions is studied for the case of a ferromagnetic monolayer with C2v symmetry like Fe/W(110). Using the quasiclassical stochastic Landau-Lifshitz-Gilbert equations, the magnon spectrum of the system is derived using linear response theory. ...
1308.2082v2
2013-08-11
New class of topological superconductors protected by magnetic group symmetries
We study a new type of three-dimensional topological superconductors that exhibit Majorana zero modes (MZM) protected by a magnetic group symmetry, a combined antiunitary symmetry composed of a mirror reflection and time-reversal. This new symmetry enhances the noninteracting topological classification of a superconduc...
1308.2424v3
2013-08-26
A Radio-Frequency-over-Fiber link for large-array radio astronomy applications
A prototype 425-850 MHz Radio-Frequency-over-Fiber (RFoF) link for the Canadian Hydrogen Intensity Mapping Experiment (CHIME) is presented. The design is based on a directly modulated Fabry-Perot (FP) laser, operating at ambient temperature, and a single-mode fiber. The dynamic performance, gain stability, and phase st...
1308.5481v2
2013-08-30
Energy dissipation of moved magnetic vortices
A two-dimensional easy-plane ferromagnetic substrate, interacting with a dipolar tip which is magnetised perpendicular with respect to the easy plane is studied numerically by solving the Landau-Lifshitz Gilbert equation. The dipolar tip stabilises a vortex structure which is dragged through the system and dissipates e...
1308.6714v1
2013-10-16
Domain wall motion in magnetic nanowires: An asymptotic approach
We develop a systematic asymptotic description for domain wall motion in one-dimensional magnetic nanowires under the influence of small applied magnetic fields and currents and small material anisotropy. The magnetization dynamics, as governed by the Landau--Lifshitz--Gilbert equation, is investigated via a perturbati...
1310.4442v1
2013-10-23
Exchange-dominated Standing Spin Wave Excitations under microwave irradiation in Ni80Fe20 Thin Films
We investigated the microwave-assisted DC voltages of ferromagnetic resonances and exchangedominated standing spin wave excitations in two different in-plane magnetized permalloy thin films via homodyne detection. The line shapes of ferromagnetic resonance spectra and the dispersion curves of ferromagnetic resonance an...
1310.6108v1
2013-10-25
Mode coupling in spin torque oscillators
A number of recent experimental works have shown that the dynamics of a single spin torque oscillator can exhibit complex behavior that stems from interactions between two or more modes of the oscillator. Examples are observed mode-hopping or mode coexistence. There has been some intial work indicating how the theory f...
1310.6791v2
2013-10-31
A Labeling Approach to Incremental Cycle Detection
In the \emph{incremental cycle detection} problem arcs are added to a directed acyclic graph and the algorithm has to report if the new arc closes a cycle. One seeks to minimize the total time to process the entire sequence of arc insertions, or until a cycle appears. In a recent breakthrough, Bender, Fineman, Gilber...
1310.8381v1
2013-11-01
Superfluid Spin Transport through Easy-Plane Ferromagnetic Insulators
Superfluid spin transport $-$ dissipationless transport of spin $-$ is theoretically studied in a ferromagnetic insulator with easy-plane anisotropy. We consider an open geometry where spin current is injected into the ferromagnet from one side by a metallic reservoir with a nonequilibrium spin accumulation, and ejecte...
1311.0288v4