Pure voltage-driven spintronic neuron based on stochastic magnetization switching behaviour

Voltage-driven stochastic magnetization switching in a nanomagnet has attracted more attention recently with its superiority in achieving energy-efficient artificial neuron. Here, a novel pure voltage-driven scheme with ~27.66 aJ energy dissipation is proposed, which could rotate magnetization vector randomly using only a pair of electrodes covered on the multiferroic nanomagnet. Results show that the probability of 180° magnetization switching is examined as a sigmoid-like function of the voltage pulse width and magnitude, which can be utilized as the activation function of designed neuron. Considering the size errors of designed neuron in fabrication, it’s found that reasonable thickness and width variations cause little effect on recognition accuracy for MNIST hand-written dataset. In other words, the designed pure voltage-driven spintronic neuron could tolerate size errors. These results open a new way toward the realization of artificial neural network with low power consumption and high reliability.

Adaptive anti-synchronization of nuclear spin generator (NSG) systems with fully uncertain parameters

This article addresses control for the chaos anti-synchronization of a high frequency oscillator nuclear spin generator (NSG), which generates and controls the oscillations of the motion of a nuclear magnetization vector in a magnetic field. Based on the Lyapunov stability theory, an adaptive control law is derived to make the states of two identical (NSG) asymptotically anti-synchronized with uncertain parameters. Finally, a numerical simulation is presented to show the effectiveness of the proposed chaos anti-synchronization scheme .

Exact ground states and domain walls in one dimensional chiral magnets

We determine exactly the phase structure of a chiral magnet in one spatial dimension with the Dzyaloshinskii-Moriya (DM) interaction and a potential that is a function of the third component of the magnetization vector, n3, with a Zeeman (linear with the coefficient B) term and an anisotropy (quadratic with the coefficient A) term, constrained so that 2A ≤ |B|. For large values of potential parameters A and B, the system is in one of the ferromagnetic phases, whereas it is in the spiral phase for small values. In the spiral phase we find a continuum of spiral solutions, which are one-dimensionally modulated solutions with various periods. The ground state is determined as the spiral solution with the lowest average energy density. As the phase boundary approaches, the period of the lowest energy spiral solution diverges, and the spiral solutions become domain wall solutions with zero energy at the boundary. The energy of the domain wall solutions is positive in the homogeneous phase region, but is negative in the spiral phase region, signaling the instability of the homogeneous (ferromagnetic) state. The order of the phase transition between spiral and homogeneous phases and between polarized (n3 = ±1) and canted (n3 ≠ ±1) ferromagnetic phases is found to be second order.

Drone-based magnetic and multispectral surveys to develop a 3D model for mineral exploration at Qullissat, Disko Island, Greenland

Mineral exploration in the West Greenland flood basalt province is attractive because of its resemblance to the magmatic sulphide-rich deposit in the Russian Norilsk region, but it is challenged by rugged topography and partly poor exposure for relevant geologic formations. On northern Disko Island, previous exploration efforts have identified rare native iron occurrences and a high potential for Ni-Cu-Co-PGE-Au mineralization. However, Quaternary landslide activity has obliterated rock exposure at many places at lower elevations. To augment prospecting field work under these challenging conditions, we acquire high-resolution magnetic and optical remote sensing data using drones in the Qullissat area. From the data, we generate a detailed 3D model of a mineralized basalt unit, belonging to the Asuk Member (Mb) of the Palaeocene Vaigat formation. A wide range of legacy data and newly acquired geo- and petrophysical, as well as geochemical-mineralogical measurements form the basis of an integrated geological interpretation of the unoccupied aerial system (UAS) surveys. In this context, magnetic data aims to define the location and the shape of the buried magmatic body, and to estimate if its magnetic properties are indicative for mineralization. High-resolution UAS-based multispectral orthomosaics are used to identify surficial iron staining, which serve as a proxy for outcropping sulphide mineralization. In addition, high-resolution UAS-based digital surface models are created for geomorphological characterisation of the landscape to accurately reveal landslide features. UAS-based magnetic data suggests that the targeted magmatic unit is characterized by a pattern of distinct positive and negative magnetic anomalies. We apply a 3D magnetization vector inversion model (MVI) on the UAS-based magnetic data to estimate the magnetic properties and shape of the magmatic body. By means of using constraints in the inversion, (1) optical UAS-based data and legacy drill cores are used to assign significant magnetic properties to areas that are associated with the mineralized Asuk Mb, and (2) the Earth’s magnetic and the paleomagnetic field directions are used to evaluate the general magnetization direction in the magmatic units. Our results indicate that the geometry of the mineralized target can be estimated as a horizontal sheet of constant thickness, and that the magnetization of the unit has a strong remanent component formed during a period of Earth’s magnetic field reversal. The magnetization values obtained in the MVI are in a similar range as the measured ones from a drillcore intersecting the targeted unit. Both the magnetics and topography confirm that parts of the target unit were displaced by landslides. We identified several fully detached and presumably rotated blocks in the obtained model. The model highlights magnetic anomalies that correspond to zones of mineralization and is used to identify outcrops for sampling. Our study demonstrates the potential and efficiency of using multi-sensor high-resolution UAS data to constrain the geometry of partially exposed geological units and assist exploration targeting in difficult, poorly exposed terrain.

Regional integration and 3D modeling of airborne geophysical data: Map of Geophysical Anomalies of Colombia for mineral resources, 2020 version

The Map of Geophysical Anomalies of Colombia for mineral resources, MAGC 2020 version compiles the geophysical information acquired, processed and interpreted by the Servicio Geológico Colombiano (SGC) since 2013. This information was collected via airborne platforms (aircrafts) using magnetometry and gamma spectrometry. This version covers approximately 547 960 km2 of the national territory in the Andean (North and Central), Eastern (Eastern Plains and Amazon) and Caribbean zones (Perijá mountain range). This information consists of 17 blocks of geoscientific interest, covered by flight lines separated by 500 and 1000m, for a total of more than 907 566 linear km of airborne information, acquired at a nominal altitude of 100 m above the ground, with a sampling resolution that was not previously available at this scale and coverage. This document presents the methodology for compiling, processing and representing the thematic coverage included in MAGC 2020: Map of Total field magnetic anomaly (TFMA), Map of the analytic signal (AS) and radiometric ternary map of the distribution of the relative concentrations of uranium, thorium and potassium. Furthermore, the work identifies 1079 magnetometric anomalies of interest, which were subsequently analyzed and modeled in the Map of magnetic sources modeled from magnetization vector inversion, which contains a total of 1297 magnetic bodies interpreted from these anomalies. Integration of available geological and metallogenic information with each of these bodies allow the suggestion of possible geological sources and possible exploration targets. The objectives of this study were to generate and integrate geophysical information to identify new areas of interest with regards to potential mineral resources, and to generate new geoscientific knowledge about Colombia for land-use planning.

Constitutive Equations for Magnetic Active Liquids

This article is focused on the derivation of constitutive equations for magnetic liquids. The results can be used for both ferromagnetic and magnetorheological fluids after the introduced simplifications. The formulation of constitutive equations is based on two approaches. The intuitive approach is based on experimental experience of non-Newtonian fluids, which exhibit a generally non-linear dependence of mechanical stress on shear rate; this is consistent with experimental experience with magnetic liquids. In these general equations, it is necessary to determine the viscosity of a liquid as a function of magnetic induction; however, these equations only apply to the symmetric stress tensor and can only be used for an incompressible fluid. As a result of this limitation, in the next part of the work, this approach is extended by the asymmetry of the stress tensor, depending on the angular velocity tensor. All constitutive equations are formulated in Cartesian coordinates in 3D space. The second approach to determining constitutive equations is more general: it takes the basis of non-equilibrium thermodynamics and is based on the physical approach, using the definition of density of the entropy production. The production of entropy is expressed by irreversible thermodynamic flows, which are caused by the effect of generalized thermodynamic forces after disturbance of the thermodynamic equilibrium. The dependence between fluxes and forces determines the constitutive equations between stress tensors, depending on the strain rate tensor and the magnetization vector, which depends on the intensity of the magnetic field. Their interdependencies are described in this article on the basis of the Curie principle and on the Onsager conditions of symmetry.

Magnetic Signature of the Saco do Mamanguá and Paraty-Mirim Cove, Rio de Janeiro, Brazil

ABSTRACT. In this work, we investigate the N40°-50°E-oriented magnetic lineaments observed in the marine and aeromagnetic data from the Paraty-Mirim and Saco do Mamanguá (RJ) coves. The main characteristic of these lineaments is the presence of normal and reverse magnetic polarity, indicating that the bodies responsible for the anomalies may be of different ages or have suffered remagnetization effects by metamorphism or have distinct lithologies. The interpretative model of the anomalies was obtained by the 3D Magnetization Vector Inversion (MVI) and by the study of the geology and tectonics of the area. Our results suggest, as a more likely hypothesis, that the magnetic lineaments can be correlated with two tholeiitic dykes swarms, Resende-Ilha Grande and Serra do Mar, which have intruded the region at different times. The age formation of those swarms can be placed at time intervals where the Earth's magnetic field has normal and reverse polarities. The contrasts of magnetic susceptibility obtained from the models are consistent with contrasts of the lithology of basic dykes intruded in the gneissic-granitic basement of the region. Keywords: magnetization vector inversion, magnetic properties, magnetic lineaments, remanent magnetization, tholeiitic dykes swarms Assinatura Magnética do Saco do Mamanguá e da Enseada de Paraty-Mirim, Rio de Janeiro, BrasilRESUMO. Neste trabalho, investigamos os lineamentos magnéticos orientados a N40°-50°E observados nos dados marinhos e aeromagnéticos das enseadas de Paraty-Mirim e do Saco do Mamanguá (RJ). A principal característica destes lineamentos é a presença de polaridade magnética normal e reversa, indicando que os corpos responsáveis pelas anomalias podem ter idades diferentes ou terem sofrido efeitos de remagnetização por metamorfismo ou apresentarem litologias distintas. O modelo interpretativo das anomalias foi obtido pela Inversão do Vetor de Magnetização (IVM) 3D e pelo estudo da geologia e tectônica da área. Nossos resultados sugerem, como hipótese mais provável, que os lineamentos magnéticos podem ser correlacionados com dois enxames de diques toleíticos, Resende-Ilha Grande e Serra do Mar, que têm idades diferentes de intrusão. As idades de formação desses enxames podem ser colocadas em intervalos de tempo em que o campo magnético da Terra apresentou polaridades normal e reversa. Os contrastes de susceptibilidade magnética obtidos no modelo são coerentes com os contrastes de litologia de diques básicos intrudidos no embasamento granítico-gnáissico da região.Palavras-chave: inversão do vetor de magnetização, propriedades magnéticas, lineamentos magnéticos, magnetização remanente, enxames de diques toleíticos

Template-Assisted Iron Nanowire Formation at Different Electrolyte Temperatures

We studied the morphology, structure, and magnetic properties of Fe nanowires that were electrodeposited as a function of the electrolyte temperature. The nucleation mechanism followed instantaneous growth. At low temperatures, we observed an increase of the total charge reduced into the templates, thus suggesting a significant increase in the degree of pore filling. Scanning electron microscopy images revealed smooth nanowires without any characteristic features that would differentiate their morphology as a function of the electrolyte temperature. X-ray photoelectron spectroscopy studies indicated the presence of a polycarbonate coating that covered the nanowires and protected them against oxidation. The X-ray diffraction measurements showed peaks coming from the polycrystalline Fe bcc structure without any traces of the oxide phases. The crystallite size decreased with an increasing electrolyte temperature. The transmission electron microscopy measurements proved the fine-crystalline structure and revealed elongated crystallite shapes with a columnar arrangement along the nanowire. Mössbauer studies indicated a deviation in the magnetization vector from the normal direction, which agrees with the SQUID measurements. An increase in the electrolyte temperature caused a rise in the out of the membrane plane coercivity. The studies showed the oxidation resistance of the Fe nanowires deposited at elevated electrolyte temperatures.

Feasibility of Fiber Reinforcement Within Magnetically Actuated Soft Continuum Robots

Soft continuum manipulators have the potential to replace traditional surgical catheters; offering greater dexterity with access to previously unfeasible locations for a wide range of interventions including neurological and cardiovascular. Magnetically actuated catheters are of particular interest due to their potential for miniaturization and remote control. Challenges around the operation of these catheters exist however, and one of these occurs when the angle between the actuating field and the local magnetization vector of the catheter exceeds 90°. In this arrangement, deformation generated by the resultant magnetic moment acts to increase magnetic torque, leading to potential instability. This phenomenon can cause unpredictable responses to actuation, particularly for soft, flexible materials. When coupled with the inherent challenges of sensing and localization inside living tissue, this behavior represents a barrier to progress. In this feasibility study we propose and investigate the use of helical fiber reinforcement within magnetically actuated soft continuum manipulators. Using numerical simulation to explore the design space, we optimize fiber parameters to enhance the ratio of torsional to bending stiffness. Through bespoke fabrication of an optimized helix design we validate a single, prototypical two-segment, 40 mm × 6 mm continuum manipulator demonstrating a reduction of 67% in unwanted twisting under actuation.

From hidden order to antiferromagnetism: Electronic structure changes in Fe-doped URu2Si2

In matter, any spontaneous symmetry breaking induces a phase transition characterized by an order parameter, such as the magnetization vector in ferromagnets, or a macroscopic many-electron wave function in superconductors. Phase transitions with unknown order parameter are rare but extremely appealing, as they may lead to novel physics. An emblematic and still unsolved example is the transition of the heavy fermion compound URu2Si2 (URS) into the so-called hidden-order (HO) phase when the temperature drops below T0=17.5 K. Here, we show that the interaction between the heavy fermion and the conduction band states near the Fermi level has a key role in the emergence of the HO phase. Using angle-resolved photoemission spectroscopy, we find that while the Fermi surfaces of the HO and of a neighboring antiferromagnetic (AFM) phase of well-defined order parameter have the same topography, they differ in the size of some, but not all, of their electron pockets. Such a nonrigid change of the electronic structure indicates that a change in the interaction strength between states near the Fermi level is a crucial ingredient for the HO to AFM phase transition.