Magnetic Patterns Research Articles

Control of magnetoelastic coupling in Ni/Fe multilayers using He+ ion irradiation

This study reports the effects of post-growth He+ irradiation on the magneto-elastic properties of a Ni/Fe multi-layered stack. The progressive intermixing caused by He+ irradiation at the interfaces of the multilayer allows us to tune the saturation magnetostriction value with increasing He+ fluences and even to induce a reversal of the sign of the magnetostrictive effect. Additionally, the critical fluence at which the absolute value of the magnetostriction is dramatically reduced is identified. Therefore, insensitivity to strain of the magnetic stack is nearly reached, as required for many applications. All the above-mentioned effects are attributed to the combination of the negative saturation magnetostriction of sputtered Ni and Fe layers and the positive magnetostriction of the NixFe1−x alloy at the intermixed interfaces, whose contribution is gradually increased with irradiation. Importantly, the irradiation does not alter the layer polycrystalline structure, confirming that post-growth He+ ion irradiation is an excellent tool to tune the magneto-elastic properties of multilayer samples. An alternative class of spintronic devices can be envisioned with a material treatment able to arbitrary change the magnetostriction with ion-induced “magnetic patterning.”

Spin wave computing using pre-recorded magnetization patterns

We propose a novel type of spin wave computing device, based on a bilayer structure that includes a “bias layer” made from a hard magnetic material and a “propagation layer” made from a magnetic material with low damping, for example, yttrium garnet or permalloy. The bias layer maintains a stable pre-recorded magnetization pattern, which generates a bias field with a desired spatial dependence, which in turn sets the equilibrium magnetization inside the propagation layer. When an external source applies an RF field to the propagation layer, excited spin waves scatter on the magnetization's inhomogeneities resulting in complex interference behavior. This scattering interference can be utilized to perform a variety of mathematical operations including Vector-Matrix multiplication. The spatial dependence of such magnetization patterns can be estimated via perturbation theory.

Characterization of Rotational Magnetic Properties of Amorphous Metal Materials for Advanced Electrical Machine Design and Analysis

Amorphous metal (AM), specifically amorphous ferromagnetic metal, is considered as a satisfactory magnetic material for exploring electromagnetic devices with high-efficiency and high-power density, such as electrical machines and transformers, benefits from its various advantages, such as reasonably low power loss and very high permeability in medium to high frequency. However, the characteristics of these materials have not been investigated comprehensively, which limits its application prospects to good-performance electrical machines that have the magnetic flux density with generally rotational and non-sinusoidal features. The appropriate characterization of AMs under different magnetizations is among the fundamentals for utilizing these materials in electrical machines. This paper aims to extensively overview AM property measurement techniques in the presence of various magnetization patterns, particularly rotational magnetizations, and AM property modeling methods for advanced electrical machine design and analysis. Possible future research tasks are also discussed for further improving AM applications.

Social cognitive processes explain bias in juror decisions.

Jury decisions are among the most consequential social decisions in which bias plays a notable role. While courts take measures to reduce the influence of non-evidentiary factors, jurors may still incorporate biases into their decisions. One common bias, crime-type bias, is the extent to which the perceived strength of a prosecutor's case depends on the severity of the crime. Moral judgment, affect and social cognition have been proposed as core processes underlying this and other biases. Behavioral evidence alone has been insufficient to distinguish these explanations. To identify the mechanism underlying crime-type bias, we collected functional magnetic resonance imaging patterns of brain activation from mock jurors reading criminal scenarios. Brain patterns from crime-type bias were most similar to those associated with social cognition (mentalizing and racial bias) but not affect or moral judgment. Our results support a central role for social cognition in juror decisions and suggest that crime-type bias and cultural bias may arise from similar mechanisms.

Vertical deformation partitioning across a collapsing large and hot orogen

AbstractFeaturing 3 000‐km‐long large and hot orogen, the Mantiqueira Province provides a rare opportunity to study the process of gravitational collapse at mid to deep crustal levels. Distinct but contemporary (~500 Ma) post‐collisional intrusions show structures and anisotropy of magnetic susceptibility (AMS) fabrics related to their emplacements, recording different flow patterns. In southern deep‐seated intrusions, ellipsoidal‐shaped roots with gabbroic‐to‐hybrid cores surrounded by granitic rocks show concentric patterns of AMS fabrics that cut across the NE‐trending regional foliation. In contrast, northern intrusions, exposed as the upper sections of batholith‐size bodies of coarse‐grained granite emplaced at the shallow to mid‐crust, show general NS‐trending magnetic fabrics roughly parallel to strike of the orogen and the regional foliation of host rocks. These contrasting magnetic patterns from shallow to deeper crust suggest vertical magma migration from the overthickened orogenic core to be emplaced across its thinner stretched flanks during the gravitational collapse of the orogenic edifice.

Unveiling the anisotropic fractal magnetic domain structure in bulk crystals of antiskyrmion host (Fe,Ni,Pd)3P by small-angle neutron scattering

Intermetallic Pd-doped (Fe,Ni)3P, which crystallizes in a non-centrosymmetric tetragonal structure with S 4 symmetry, has recently been discovered to host magnetic antiskyrmions, antivortex-like topological spin textures. In this material, uniaxial magnetic anisotropy and dipolar interactions play a significant role, giving rise to finely branched magnetic domain patterns near the surface of bulk crystals, as revealed by a previous magnetic force microscopy (MFM) measurement. However, small-angle neutron scattering (SANS) is a more suitable method for characterizing bulk properties and fractal structures on the mesoscopic length scale. In this study, using SANS and MFM, the magnetic domain structure in bulk single crystals of (Fe0.63Ni0.30Pd0.07)3P is quantitatively investigated. The SANS results demonstrate that the magnetic domain structure exhibits anisotropic fractal character on length scales down to the width of the magnetic domain walls. The fractal features are gradually lost in magnetic fields, and different field dependencies are observed at 300 and 2 K due to a temperature-dependent anisotropy. This study quantifies the fractality of the highly anisotropic magnetic domain structures in an antiskyrmion material, and highlights the versatility of SANS for the study of fractal structures in magnetic systems.

Adiabatic and irreversible classical discrete time crystals

We simulate the dynamics of paramagnetic colloidal particles that are placed above a magnetic hexagonal pattern and exposed to an external field periodically changing its direction along a control loop. The conformation of three colloidal particles above one unit cell adiabatically responds with half the frequency of the external field creating a time crystal at arbitrary low frequency. The adiabatic time crystal occurs because of the non-trivial topology of the stationary manifold. When coupling colloidal particles in different unit cells, many body effects cause the formation of topologically isolated time crystals and dynamical phase transitions between different adiabatic reversible and non-adiabatic irreversible space-time-crystallographic arrangements.

The Sun’s Mean Line-of-sight Field

In this paper, I regard the Sun-as-a-star magnetic field (i.e., the mean field) as a filter for the spherical harmonic components of the photospheric field, and then calculate the transmission coefficients of this filter. The coefficients for each harmonic, Y l m , are listed in three tables according to their dependence on B 0, the observer’s latitude in the star’s polar coordinate system. These coefficients are used to interpret the 46 yr sequence of daily mean-field measurements at the Wilcox Solar Observatory. I find that the nonaxisymmetric part of the field originates in the , , and a combination of the and harmonic components. The axisymmetric part of the field originates in plus a B 0-dependent combination of the and components. The power spectrum of the field has peaks at frequencies corresponding to the ∼27 day synodic equatorial rotation period and its second and third harmonics. Each of these peaks has fine structure on its low-frequency side, indicating magnetic patterns that rotate slowly under the influence of differential rotation and meridional flow. The sidebands of the fundamental mode resolve into peaks corresponding to periods of ∼28.5 and ∼30 days, which tend to occur at the start of sunspot maximum, whereas the ∼27 day period tends to occur toward the end of sunspot maximum. We might expect similar rotational sidebands to occur in magnetic observations of other Sun-like stars and to be a useful complement to asteroseismology studies of convection and magnetic fields in those stars.

First-principles study of charge-ordered insulating phases in Ruddlesden-Popper LaSr2V2O7

We investigate the electronic properties of Ruddlesden-Popper LaSr2V2O7 using first-principles density functional theory. By substituting La to Sr in the experimentally reported Ruddlesden-Popper Sr3V2O7 we find the charge-ordered insulating phases. The charge ordering is induced from the average nominal valence of V3.5+ by La-substitution, which in turn disproportionates to a 1:1 ratio of V4+ and V3+ sites. The charge ordering is accompanied by the uniaxial Jahn-Teller distortion compatible with the charge ordering pattern where compression (elongation) along the [11̄0]-direction lowers dxz (dxy/dyz) orbitals with respect to the other t2g orbitals. The comparison of total energies with different charge and magnetic ordering patterns shows that the ground state is insulating with a checkerboard-type of charge ordering and an A-type (layered) antiferromagnetic ordering. Our work, proposing a new charge-ordered insulating phase by A-site substitution, provides an effective way to design insulating oxides with charge ordering.

Quasi-linear and Plateaus-like Tunneling Magnetoresistance in Graphene-based Tunable Magnetic Barrier Nanostructures

The effect of electrostatic and magnetic vector potentials pattern on electrical properties and the tunneling magnetoresistance in graphene junction with periodic magnetic vector potentials are theoretically investigated using the transfer matrix method. The magnetic structure on graphene can control the direction of the magnetizations which correspond to the parallel and anti-parallel (AP) configurations. In AP magnetic structures with the applied gate voltage pattern, USUBA/SUB (U₁ = U₂), the shift of the conductance-peak position as a function of Fermi energy. The peak corresponds to resonant tunneling, where the incidence energy of the tunneling electron equals the confinement energy, and the conductance peak decrease approximately linearly with increasing electrostatic potential. The peak position occurs at ESUBF/SUB = 0.5U where it is shifted to higher Fermi energy with higher gate potential, but for the case of USUBB/SUB (U₁ = -U₂), the peak height is reduced rapidly, and the width increase as gate potential increases. Because of the periodic magnetic field with zero spatial average in the antiparallel structure, we found that the minimum conductivity decreases with increasing magnetic energy. They show suppression of Klein tunneling which occurs in the zero-conductance plateaus and leads to the robust magnetoresistance plateau and large positive magnetoresistance appears below magnetic energy. For the case of USUBA/SUB and ESUBF/SUB more than magnetic energy, we found that the quasi-linear magnetoresistance feature is applied by an electric field instead of the usual magnetically driven magnetoresistance.

Spin fluctuations in the 112-type iron-based superconductor Ca0.82La0.18Fe0.96Ni0.04As2

We report time-of-flight inelastic neutron scattering (INS) investigations on the spin fluctuation spectrum in the 112-type iron-based superconductor (FeSC) Ca0.82La0.18Fe0.96Ni0.04As2 (CaLa-112). In comparison to the 122-type FeSCs with a centrosymmetric tetragonal lattice structure (space group ) at room temperature and an in-plane stripe-type antiferromagnetic (AF) order at low temperature, the 112 system has a noncentrosymmetric structure (space group ) with additional zigzag arsenic chains between Ca/La layers and a magnetic ground state with similar wavevector but different orientations of ordered moments in the parent compounds. Our INS study clearly reveals that the in-plane dispersions and the bandwidth of spin excitations in the superconducting CaLa-112 closely resemble to those in 122 systems. While the total fluctuating moments /Fe are larger than 122 system, the dynamic correlation lengths are similar (ξ ≈ 10 Å). These results suggest that superconductivity in iron arsenides may have a common magnetic origin under similar magnetic exchange couplings with a dual nature from local moments and itinerant electrons, despite their different magnetic patterns and lattice symmetries.

The role and contribution of magnetic fields, characterized via their magnetic flux, to the statistical structuring of the solar atmosphere

The anomalous heating of the solar upper atmosphere is one of the eight key problems in modern astronomy. Moreover, the stratification of the solar atmosphere is an outstanding key-problem in solar physics. In this study, a hot butterfly-like pattern is found to run through the chromosphere to the corona lying right on top of the magnetic butterfly pattern of sunspots in the photosphere. We thus propose to introduce the term butterfly body to describe the butterfly diagram in the 3-dimensional atmosphere. Besides, we discuss the so-called polar brightening in different layers. It is found to be statistically in anti-phase with the solar cycle in the photosphere and the chromosphere, while in phase with the solar cycle in the corona. Accordingly, we describe the role and relationship of solar magnetic elements of different magnetic flux strengths to explain the statistical structuring of the solar atmosphere with the butterfly body over the solar cycle.

Circular stripe domains and cone state vortices in disk-shaped exchange coupled magnetic heterostructures

Vertically stacked exchange coupled magnetic heterostructures of cylindrical geometry can host complex noncolinear magnetization patterns. By tuning the interlayer exchange coupling between a layer accommodating magnetic vortex state and an out-of-plane magnetized layer, one can efficiently realize new topological chiral textures such as cone state vortices and circular stripe domains. We study how the number of circular stripes can be controlled by both the interlayer exchange coupling and the sample geometrical parameters. By varying geometrical parameters, a continuous phase transition between the homogeneous state, cone state vortex, circular stripe domains, and the imprinted vortex takes place, which is analysed by full scale micromagnetic simulations. The analytical description provides an intuitive pictures of the magnetization textures in each of these phases. The possibility to realize switching between different states allows for engineering magnetic textures with possible applications in spintronic devices.

Design of Arbitrary Magnetic Patterns on Magnetic Polymer Composite Objects: A Finite Element Modelling Tool.

Magnetic sensor systems integrate a sensing element and magnetic field generators to determine their relative position or to measure movement. Typically, the magnetic fields are produced by permanent magnets, which have high intensity but are hard to machine into custom shapes. However, novel solutions using magnetic polymer composites (MPCs) have emerged as field generators due to their low cost, weight and patterning freedom. Here, we present a finite element model developed in COMSOL Multiphysics that allows the design of complex magnetization patterns on these polymer composites, taking into account the geometries of the parts and the magnetic properties of the materials employed. The model, together with the characterization protocol of the materials, has proved to be capable of predicting the magnetization of polymer composites at different temperatures. In addition, the model incorporates the properties of the magnets used during the magnetization process, such as the size, shape and magnetization, as well as the properties of the surrounding elements. This new model facilitates the design of new polymeric parts with complex shapes and magnetization patterns that can be employed as field generators in magnetic sensing systems.

Magnetic domain scanning imaging using phase-sensitive THz-pulse detection

In our study, we determine the alignment of magnetic domains in a CoFeB layer using THz radiation. We generate THz pulses by fs laser pulses in magnetized CoFeB/Pt heterostructures based on spin currents. An LT-GaAs Auston switch detects the radiation phase sensitively and allows us to determine the magnetization alignment. Our scanning technique with motorized stages, with step sizes in the sub-micrometer range, allows us to image two dimensional magnetic structures. Theoretically, the resolution is restricted to half of the wavelength if focusing optics in the far-field limit are used. By applying near-field imaging, the spatial resolution is enhanced to the single digit micrometer range. For this purpose, spintronic emitters in diverse geometric shapes, e.g., circles, triangles, squares, and sizes are prepared to observe the formation of magnetization patterns. The alignment of the emitted THz radiation can be influenced by applying unidirectional external magnetic fields. We demonstrate how magnetic domains with opposite alignment and different shapes divided by domain walls are created by demagnetizing the patterns using minor loops and imaged using phase sensitive THz radiation detection. For analysis, the data are compared to Kerr microscope images. The possibility of combining this method with THz range spectroscopic information of magnetic texture or antiferromagnets in direct vicinity to the spintronic emitter makes this detection method interesting for a much wider range of applications probing THz excitation in spin systems with high resolution beyond the Abbe diffraction limit, limited solely by the laser excitation area.

Soft Magneto‐Responsive Shape Memory Foam Composite Actuators

AbstractSoft magnetic composites are exceptional because they can be controlled remotely, move quickly, conform to hard things, and interact with people safely. However, even with all these features, magnetic elastomers suffer a lack of stability due to the high softness of the elastomer. This issue affects their controllability and repeatability. This article introduces a novel conceptual design of magneto‐responsive shape memory polyurethane (SMP) foam composites with high stability and reversibility. The fabrication technique is based on the silicone resins filled with strontium ferrite magnetic particles and a thin SMP foam placed onto one side. Material properties, room‐temperature shape recovery features, and magnetization conditions necessary for the process are determined by experimental studies of composite actuators. As a result, a workable, light, stable, soft composite gripper with programmable magnetic patterns is created, which can carry out activities like grabbing, holding, and moving objects in horizontal and vertical directions when a low magnetic field is applied. The SMP foam increases the contact surface and decreases the weight by up to three times providing better stability compared to the magnetic elastomer without SMP foam. The shape‐recoverable gripper with a small contract area can lift objects eight times heavier than its weight.

Cardiovascular magnetic resonance imaging patterns of acute COVID-19 mRNA vaccine-associated myocarditis in young male patients: A first single-center experience.

BackgroundThe risk of myocarditis after mRNA vaccination against COVID-19 has emerged recently. Current evidence suggests that young male patients are predominantly affected. In the majority of the cases, only mild symptoms were observed. However, little is known about cardiac magnetic resonance (CMR) imaging patterns in mRNA-related myocarditis and their differences when compared to classical viral myocarditis in the acute phase of inflammation.Methods and resultsIn total, 10 mRNA vaccination-associated patients with myocarditis were retrospectively enrolled in this study and compared to 10 patients suffering from viral myocarditis, who were matched for age, sex, comorbidities, and laboratory markers. All patients (n = 20) were hospitalized and underwent a standardized clinical examination, as well as an echocardiography and a CMR. Both, clinical and imaging findings and, in particular, functional and volumetric CMR assessments, as well as detailed tissue characterization using late gadolinium enhancement and T1 + T2-weighted sequences, were compared between both groups. The median age of the overall cohort was 26 years (group 1: 25.5; group 2: 27.5; p = 0.57). All patients described chest pain as the leading reason for their initial presentation. CMR volumetric and functional parameters did not differ significantly between both groups. In all cases, the lateral left ventricular wall showed late gadolinium enhancement without significant differences in terms of the localization or in-depth tissue characterization (late gadolinium enhancement [LGE] enlargement: group 1: 5.4%; group 2: 6.5%; p = 0.14; T2 global/maximum value: group 1: 38.9/52 ms; group 2: 37.8/54.5 ms; p = 0.79 and p = 0.80).ConclusionThis study yielded the first evidence that COVID-19 mRNA vaccine-associated myocarditis does not show specific CMR patterns during the very acute stage in the most affected patient group of young male patients. The observed imaging markers were closely related to regular viral myocarditis in our cohort. Additionally, we could not find any markers implying adverse outcomes in this relatively little number of patients; however, this has to be confirmed by future studies that will include larger sample sizes.

Macroscopic magnetic hardening due to nanoscale spinodal decomposition in Fe–Cr

The Fe–Cr alloy system is the basis of ferritic steels, which are important structural materials for many applications, including their use in future fusion reactors. However, when exposed to elevated temperatures and radiation, the Fe–Cr system can undergo phase separation, resulting in Fe-rich (α) and Cr-rich (α’) nanoscale regions. This in turn generates the so-called “475 °C embrittlement” and modifies the magnetic properties. The correlation between the microstructural and magnetic changes is however poorly understood, which currently prevents the possibility of assessing the material in a non-destructive way by magnetometry. Here, we study the microstructural decomposition of an Fe–40Cr alloy induced by annealing at 500 °C for extensive time scales and its impact on the magnetic properties using magnetometry and advanced experimental methods, such as atom probe tomography, transmission electron microscopy (TEM), and micromagnetic simulations. Upon annealing, the alloy rapidly exhibits a spinodal decomposition morphology with a typical length scale of about 10 nm. With increasing annealing time, the hardness assessed by Vickers testing, the magnetic saturation, and the coercivity increase, which correlates with an increase in α-volume fraction and the system's heterogeneity. The magnetic domain patterns imaged by TEM and interpreted with the help of micromagnetic simulations reveal at the nanometer scale the impact of decomposition on the magnetic response of Fe–Cr.

Superparamagnetic Iron Oxide Nanoparticles for Targeted Cell Seeding: Magnetic Patterning and Magnetic 3D Cell Culture

AbstractIn regenerative medicine, noncontact manipulation of cells enables new possibilities for tissue engineering. Due to their physicochemical properties, superparamagnetic iron oxide nanoparticles (SPIONs) are used in biomedicine for various applications, e.g., as drug transporters, contrast agents or to make cells maneuverable by magnetic forces. SPIONs attached to and/or taken up by cells enable their magnetic targeting for adoptive immune therapies or tissue engineering. Remote control of different “magnetized” cell types can be used to construct multilayered tissues without the need for a scaffold structure. Here, the suitability of SPIONs with various coatings, such as polyacrylic acid‐co‐maleic acid (PAM), lauric acid (LA), lauric acid‐human serum albumin (HSA), and citrate to magnetize cells is compared with the commercially available NanoShuttle‐PL, designed for use in magnetic 3D cell cultures. Depending on the amount of cellular labeling, magnetic control is more or less effective. In particular, PAM‐ and citrate‐coated SPIONs achieve good cellular loading and provide magnetic controllability of cells. In 2D cell culture, the magnetic cargo allows the patterned culture of cells. In 3D, SPIONs enable and accelerate spheroid formation as well as micropatterning using unloaded and loaded cells in parallel.

Band processing of Landsat 8-OLI multi-spectral images as a tool for delineating alteration zones associated with porphyry prospects: A case from Suyoc, Benguet, Philippines

The Mankayan Mineral District in Luzon is marked by several porphyry and epithermal mineralizations. The possibility of blind porphyry mineralization in Mangga, Basig, and Palidan was forwarded based on the results of recent ground magnetic surveys in Suyoc, Mankayan, Benguet. These areas exhibited the diagnostic magnetic anomaly patterns expected of porphyry copper deposits. This signature, a magnetic core surrounded by a non-magnetic rim, is due to the alteration haloes common to porphyry systems. The magnetic core corresponds to the potassic zone dominated by iron-oxide-bearing minerals (e.g., magnetite). Meanwhile, the abundance of non-magnetic clay minerals at the periphery of the mineralized region corresponds to propylitic-argillic alteration zones. Delineation of alteration zones using remote sensing was done to further support the suggested mineralization prospects. Mixture tuned matched filtering (MTMF) was carried out to reduce the effects of vegetation cover from Landsat 8 data. Principal Components Analysis (PCA) was applied to generate bands exploiting the greatest difference between the clay and magnetite alterations with background earth materials. A classified composite map depicts the altered regions. The three sites previously identified from magnetic anomalies also display the expected alterations. Another prospect in the Lapangan area is being proposed based on magnetic anomalies and mapped alterations.