Magnetic Thickness Research Articles

Tuning ferromagnetic resonance via disorder/order interfaces

Ferromagnetic resonance of a thin film alloy has been tuned by inducing lateral interfaces between layers differing in their lattice ordering and magnetic properties. By disordering B2 Fe60Al40 thin films to the A2 structure, thereby manifesting planar A2/B2 interfaces at selected depths, we show that the resonance lines at 10 GHz are shifted by 284 mT and 35 mT for fields applied perpendicular-to-plane and in-plane, respectively. The resonance line shift occurs over a broad frequency range and is driven by strain relaxation due to the increasing magnetic layer thickness. A finer anomalous line shift occurs as the A2/B2 interface approaches the film/substrate interface prior to being expelled from the film. The A2 structure can be reannealed to the B2 order, implying that disorder/order interface modification can provide a path for reversibly encoding resonant properties in alloy thin films.

High Torque Density and Low Torque Ripple Shaped-Magnet Machines Using Sinusoidal Plus Third Harmonic Shaped Magnets

This paper proposes a novel shaped-magnet surface permanent magnet machine design concept featuring magnets shaped according to a sinusoid plus a third harmonic along the axial direction, and full-pole-pitched distributed stator windings with a unity winding factor to provide high torque density with essentially zero torque ripple for high-performance motor applications. The magnet thickness is uniform along the radial direction so as not to impair the magnet's ability to handle the demagnetization force. The proposed design was compared against a full-pole-pitched magnet design with maximum magnetic loading and a conventional bread-loaf magnet design. The results demonstrate that the proposed shaped-magnet design uses the magnet materials efficiently to achieve torque density comparable to that of the full-pole-pitched magnet design, and essentially zero torque ripple without compromising its resistivity against a demagnetization force, which conventional bread-loaf magnets cannot offer.

Optimization of a High-Temperature Starter—Generator of Inverted Design for Aircraft

A high-temperature starter-generator with an outer rotor and the possibility of arranging it on the high-pressure shaft of ab aircraft engine are considered. The materials to manufacture this starter-generator were selected, numerical calculations of it were performed, and various world analogs were considered. Based on the obtained data, a multicriterion optimization of the design scheme was performed by means of a genetic algorithm and the Pareto method. As a result of optimization, a Pareto optimal active length and thickness of permanent magnets of the starter-generator were chosen. Using the obtained sizes made it possible to reduce the weight of the designed starter-generator by 10 kg relative to the basic variant (of the foreign high-temperature starter-generator produced by Thales) with invariable thermal loads. On the basis of the optimal geometrical dimensions, a multidisciplinary computer simulation (interdependent thermal, electromagnetic, and mechanical calculations) was performed, as a result of which the viability of the designed structure was demonstrated.

Fabrication and Characterization of CoFe2O4 and MnFe2O4 Nanomagnetic Thin Films for RF Applications

In order to have magnetic films with better radio frequency (RF) properties that can be utilized in a wide range of microwave devices and circuits, such as frequency selective limiters, tunable filters, and antennas, this paper presents the fundamental studies on ferromagnetic resonance (FMR) of magnetic nanoparticles, the fabrication process of the magnetic nanoparticle films, and the scattering parameters measurement results of the magnetic nanoparticle films on a microstrip RF line. We explore the FMR profiles of various magnetic nanoparticles and their corresponding magnetic susceptibilities. Two novel methods, the layer-by-layer (LbL) process and the solution cast (SC) method, are proposed to deposit cobalt ferrite (CoFe2O4) and manganese ferrite nanoparticles (MnFe2O4) on soda-lime glass substrates to fabricate magnetic films with various thicknesses (2.5– $125~\mu \text{m}$ ). In addition, a 3-D printed RF transmission line integrating the magnetic film is used to test the effect of the magnetic nanoparticles. By comparing the measured group delays of microstrip lines with different films, we can obtain some insights into the relationship of the magnetic film thickness, types of magnetic materials, deposition methods, and the amount of the group delay. Specifically, thicker films result in higher group delay, and the SC method is more efficient in fabricating thicker films than the LbL process. The fill factor of these two methods, however, shows that the LbL process generates higher particle loading in the films, while the SC films have considerably more organic binders inside to maintain them. Given the same film thickness, manganese ferrite nanoparticles bring higher group delay than the cobalt ferrite nanoparticles. This paper proposes new methods of fabricating thicker nanomagnetic films and explores the characterization of different magnetic materials with various film thicknesses. It, therefore, paves the way for fabricating monolithic microwave devices and circuits utilizing nanomagnetic materials.

Divergent patterns of TDP-43 and tau pathologies in primary progressive aphasia.

To measure postmortem burden of frontotemporal lobar degeneration (FTLD) with TDP-43 (FTLD-TDP) or tau (FTLD-Tau) proteinopathy across hemispheres in primary progressive aphasia (PPA) using digital histopathology and to identify clinicopathological correlates of these distinct proteinopathies. In an autopsy cohort of PPA (FTLD-TDP = 13, FTLD-Tau = 14), we analyzed laterality and regional distribution of postmortem pathology, quantified using a validated digital histopathological approach, in available brain tissue from up to 8 cortical regions bilaterally. We related digital pathology to antemortem structural neuroimaging and specific clinical language features. Postmortem cortical pathology was left-lateralized in both FTLD-TDP (beta = -0.15, standard error [SE] = 0.05, p = 0.007) and FTLD-Tau (beta = -0.09, SE = 0.04, p = 0.015), but the degree of lateralization decreased with greater overall dementia severity before death (beta = -8.18, SE = 3.22, p = 0.015). Among 5 core pathology regions sampled, we found greatest pathology in left orbitofrontal cortex (OFC) in FTLD-TDP, which was greater than in FTLD-Tau (F = 47.07, df = 1,17, p < 0.001), and in left midfrontal cortex (MFC) in FTLD-Tau, which was greater than in FTLD-TDP (F = 19.34, df = 1,16, p < 0.001). Postmortem pathology was inversely associated with antemortem magnetic resonance imaging cortical thickness (beta = -0.04, SE = 0.01, p = 0.007) in regions matching autopsy sampling. Irrespective of PPA syndromic variant, single-word comprehension impairment was associated with greater left OFC pathology (t = -3.72, df = 10.72, p = 0.004) and nonfluent speech with greater left MFC pathology (t = -3.62, df = 12.00, p = 0.004) among the 5 core pathology regions. In PPA, FTLD-TDP and FTLD-Tau have divergent anatomic distributions of left-lateralized postmortem pathology that relate to antemortem structural imaging and distinct language deficits. Although other brain regions may be implicated in neural networks supporting these complex language measures, our observations may eventually help to improve antemortem diagnosis of neuropathology in PPA. Ann Neurol 2019;85:630-643.

Preparation and nanoscale characterization of electrodeposited CoFe-Cu multilayer nanowires

CoFe-Cu multilayered nanowires have been fabricated by pulse electrodeposition into the pores of ∼100 nm diameter anodized aluminum oxide (AAO) templates. Here, we investigate three samples, where the magnetic layer thickness is increased by extending the pulse time tCoFe 10 s, 13 s and 16 s while keeping the non-magnetic layer thickness constant (tCu = 30 s). Scanning electron microscopy and transmission electron microscopy confirm uniform, continuous and densely packed wires. By increasing the CoFe deposition time the aspect ratio enhanced and a layer stacking is demonstrated. The EDX line scan along the single nanowire indicates that they are Cu-rich with the composition of 10–15% Co, 0–5% Fe and 75–80% Cu. Magnetic measurements reveal a temperature dependency of the coercivity. The increase in coercivity is associated with the inherent shape and magnetocrystalline anisotropy of the nanowires. Magnetic measurements at low temperature exhibited the increase in coercivity of CoFe-Cu nanowires as a result of the freezing of thermal fluctuations.

Manipulation of magnetic skyrmions in a locally modified synthetic antiferromagnetic racetrack

In skyrmion-based racetrack memories, the information encoded by skyrmions may be destroyed due to the skyrmion Hall effect, which can be surmounted by using synthetic antiferromagnetic racetracks. Hence, the manipulation of skyrmions in synthetic antiferromagnetic racetracks is important for practical applications. Here, we computationally study the interaction between a pair of skyrmions and a locally modified region in a synthetic antiferromagnetic racetrack, where the perpendicular magnetic anisotropy or thickness is locally adjusted to be different from that of the rest region of the racetrack. It is found that the skyrmions can be attracted, repelled, and even trapped by the locally modified region in a controllable manner. Besides, we demonstrate that the skyrmion location can be precisely determined by the locally modified region. The possible manipulation of skyrmions by utilizing locally modified regions in a synthetic antiferromagnetic racetrack may be useful for future skyrmion-based applications.

Exploring interfacial exchange coupling and sublattice effect in heavy metal/ferrimagnetic insulator heterostructures using Hall measurements, x-ray magnetic circular dichroism, and neutron reflectometry

We use temperature-dependent Hall measurements to identify contributions of spin Hall, magnetic proximity, and sublattice effects to the anomalous Hall signal in heavy metal/ferrimagnetic insulator heterostructures with perpendicular magnetic anisotropy. This approach enables detection of both the magnetic proximity effect onset temperature and the magnetization compensation temperature and provides essential information regarding the interfacial exchange coupling. Onset of a magnetic proximity effect yields a local extremum in the temperature-dependent anomalous Hall signal, which occurs at higher temperature as magnetic insulator thickness increases. This magnetic proximity effect onset occurs at much higher temperature in Pt than W. The magnetization compensation point is identified by a sharp anomalous Hall sign change and divergent coercive field. We directly probe the magnetic proximity effect using x-ray magnetic circular dichroism and polarized neutron reflectometry, which reveal an antiferromagnetic coupling between W and the magnetic insulator. Finally, we summarize the exchange-coupling configurations and the anomalous Hall-effect sign of the magnetized heavy metal in various heavy metal/magnetic insulator heterostructures.

Analysis of a Flux Reversal Machine With Quasi-Halbach Magnets in Stator Slot Opening

Flux reversal permanent magnet (FRPM) machine, with magnets mounted on or inserted into the stator, is favorable for the direct drive applications. In this paper, an FRPM machine with Quasi-Halbach array magnets in stator slot opening is introduced. The operation principle of the proposed machine is presented, and the combination of stator and rotor slot number is given. Several key parameters, that are split ratio, stator and rotor slot opening ratio, magnet ratio, and magnet thickness are carefully investigated, while four proposed FRPM machines with 12 stator slots and 10, 11, 13, 14 rotor slots are optimized for better performance. Moreover, the proposed FRPM machine is compared with a conventional FRPM machine, the analysis results indicate that the torque density of proposed machine is 2.2 times that of the conventional FRPM machine under the same copper loss with almost the same magnet usage. Finally, a 12 stator slot/10 rotor slot FRPM prototype is built to verify the theoretical analysis.

The Effect of Cone Additional Permanent Magnet Thickness on Magnetic Field Distribution and the Levitation Force of Single Domain GdBCO Bulk Superconductor

It has been investigated that the interaction force between truncated cone permanent magnet (PM) and a GdBCO bulk (HTSC) superconducting permanent magnet (SCPM) magnetized by a truncated cone permanent magnet in their configurations at 77K. The influence of two configurations in different thickness of truncated cone permanent magnets of single domain GdBCO bulk capture field and superconducting magnetic levitation force results. The maximum superconducting magnetic levitation force first increases as H increase, and then decreases with H when it reaches a certain value, from 5.7N to 16.6N at first, and then it decreases to 3.8N. The vertical component of the magnetic field intensity on the top surface (h=2mm) of truncated cone permanent magnet first increases, and then decreases also, from 0.20T to 0.54T, and then decrease to 0.25T. These results indicate that the levitation force of high temperature superconductor bulk can be effectively improved by scientific choosing of shape and size of permanent magnet, and reasonable designing of the system configurations, which is very important during the practical design and applications of superconducting magnetic levitation system.

Nanomagnets for ultra-high field MRI: Magnetic properties and transverse relaxivity of silica-coated ε-Fe2O3

Abstract Magnetic nanoparticles of iron oxides have received extensive attention in the biomedical research, e.g. as prospective contrast agents for T2-weighted magnetic resonance imaging (MRI). The ability of a contrast agent to enhance the relaxation rate of 1H nuclei in its vicinity is quantitatively described by its relaxivity. Among the polymorphs of the iron(III) oxide, the nanoparticulate e-Fe2O3, distinguished by its high magnetocrystalline anisotropy resulting in a blocked state of single-domain particles up to the Curie temperature of ∼500 K, has never been studied as a contrast agent for MRI before. We analyzed r1 and r2 relaxivities of e-Fe2O3 nanoparticles coated with amorphous silica, particularly with the aim to determine their dependences on the external magnetic field, temperature, and thickness of the silica coating. The r2 relaxivity was interpreted within the motional averaging and static dephasing regimes. MRI images at 11.75 T confirmed high applicability of e-Fe2O3-based contrast agents in ultra-high fields. We present the first case study considering e-Fe2O3 nanomagnets for prospective application in biomedicine, in particular for MRI in ultra-high fields. The study is complemented by a thorough investigation of magnetic properties of the nanoparticles, revealing some interesting anomalies.

Effects of carbon nanotube reinforcements on vibration suppression of magnetorheological fluid sandwich beam

Vibration suppression of a carbon nanotube–reinforced sandwich beam with magnetorheological fluid core is numerically investigated by employing the differential quadrature method. The beam has functionally graded carbon nanotube–reinforced composite base and constraining layers while its core layer is made of magnetorheological fluid. Four different types of distribution of carbon nanotubes along the thickness direction are considered. The extended rule of mixture is used to explain the effective material properties of the base and constraining layers of the beam. The equations of motion and corresponding boundary conditions are derived by applying Hamilton’s principle, and then these coupled differential equations are transformed into a set of algebraic equation applying the differential quadrature method. Natural frequencies and loss factors are extracted and compared with those available in literature. Convergence study has been performed to verify stability of the method. Effects of various parameters such as magnetic field intensity, mode number, and thickness of the magnetorheological fluid core layer on the natural frequencies and loss factors are studied.

Ion irradiation driven changes of magnetic anisotropy in ultrathin Co films sandwiched between Au or Pt covers

Abstract Modifications of magnetic anisotropy of 30 keV Ga+ ion irradiated ultrathin Co films sandwiched between Au or Pt buffer and capping layers are investigated as a function of magnetic layer thickness, dCo, and the ion fluence, F. Maps (dCo, F) of saturation fields have been derived from local magnetooptical polar Kerr effect (PMOKE) measurements. The areas with increased remanent magnetization and/or saturation fields, which are directly related to the uniaxial anisotropy, adopt linear shapes for the two branches in the maps. They are very distinct, especially for the Pt/Co/Pt system irradiated at lower and higher fluence. Replacement of Pt with Au in the buffer layer results in minor influence on the magnetization properties of the irradiated trilayers. Au as a capping layer significantly decreases the anisotropy in the branch appearing at lower fluence. In the Au/Pt/Au sandwich, a severe reduction of induced anisotropy is observed in both branches. The proposed phenomenological model describing experimentally investigated magnetic anisotropies enables separation of surface and volume contributions to both branches of enhanced anisotropy.

Enhanced transdermal permeation and anti-inflammatory potential of phospholipids complex-loaded matrix film of umbelliferone: Formulation development, physico-chemical and functional characterization

In the present study, umbelliferone - phospholipids complex - loaded matrix film (UPLC – MF) was developed with a goal of improving transdermal permeation and anti-inflammatory potential of umbelliferone (UMB). Umbelliferone – phospholipids complex (UPLC) was prepared using solvent evaporation method. UPLC-MF was prepared by simple and reproducible solvent casting method. Prepared UPLC and UPLC-MF were both physico-chemically characterized by Fourier transforms infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), powder x-ray diffraction (PXRD), proton nuclear magnetic resonance spectroscopy (1H NMR), weight variation, thickness, tensile strength, folding endurance, % elongation, moisture content and uptake Functional characterization of UPLC and UPLC-MF was carried out by solubility analysis, in vitro dissolution, diffusion, and ex vivo permeation via dialysis and biological membrane. UPLC – MF was also evaluated for in vivo anti-inflammatory activity using carrageenan-induced Albino rat paw model. Design-based optimal values for formulation and process variables of UPLC were observed to be 1:1.78, 50 °C and 2 h, respectively. Physico-chemical characterization confirmed the formation of the complex and the film. UPLC demonstrated a higher aqueous solubility (~11-fold), compared to pure UMB. Rate and extent of dissolution of UMB from UPLC was enhanced significantly to that of pure UMB. Compared to UMB-MF, the diffusion and permeation rate of UMB from UPLC-MF enhanced significantly. The UPLC – MF improved the anti-inflammatory potential of UMB by significant enhancement of edema inhibition (%), compared to UMB-MF. The obtained results showed that the present combined formulation system could be employed as a promising strategy for improving transdermal permeation of UMB.

Tubular unified magnetic‐field flux‐switching PMLM for free‐piston energy converter

A tubular flux-switching permanent-magnet linear machine (PMLM), which features unified magnetic field between the mover and two stators, is investigated for free-piston energy converter. The topology evolution, topology, operating principle and design considerations of the machine are thoroughly analysed. With the sinusoidal speed characteristic of free-piston Stirling engine considered, a tubular unified magnetic-field flux-switching PMLM is designed by finite-element analysis. Several main structural parameters, which include the outer and inner radius of the mover, the mover tooth width, the magnet thickness, the tooth widths of both the outer and inner stators and the widths of both the outer and inner stator yokes are studied to achieve high-force and mass-power density. Finally, the proposed machine is compared with two typical flux-switching PMLMs. The comparison results show that the unified magnetic-field flux-switching PMLM is suitable for applications which require high-power density, light mover structure and fast dynamic.

Moderate Physical Activity and Prevention of Cartilage Loss in People With Knee Osteoarthritis: Data From the Osteoarthritis Initiative.

To examine the impact of physical activity on cartilage thickness loss in knee osteoarthritis (OA). A total of 689 participants with radiographic knee OA at baseline (Kellgren/Lawrence grade ≥2) from the Osteoarthritis Initiative completed the Physical Activity Scale for the Elderly (PASE) questionnaires at annual intervals over 4 years. Magnetic resonance imaging-based cartilage thickness change in the medial femorotibial compartment (MFTC) over 4 years was the main outcome. The impact of PASE tertiles (low, moderate, or high) on changes in MFTC cartilage thickness was estimated using a mixed-effects model adjusted for baseline characteristics. Furthermore, stratification by sex was performed for secondary analyses. Structural progression of MFTC cartilage loss of -0.20 mm (95% confidence interval [95% CI] -0.22, -0.17) was observed in the entire cohort, with no significant difference between physical activity levels after adjustment for baseline characteristics. An interaction between sex and physical activity was observed in the adjusted analysis (P = 0.02). Stratification by sex showed that women with low physical activity had a statistically greater cartilage loss than women with moderate physical activity (adjusted between-group difference -0.09 mm [95% CI -0.16, 0.02]), whereas no significant differences were observed in men. While physical activity was not associated with cartilage thickness loss in the whole cohort, this relationship significantly differed between sexes. In women, but not in men, moderate physical activity may slow down structural disease progression compared to low physical activity levels. For both men and women, high physical activity levels do not appear to be more detrimental than lower physical activity levels for cartilage thickness loss.

Torque Ripple Optimization of a Novel Cylindrical Arc Permanent Magnet Synchronous Motor Used in a Large Telescope

This paper proposes the use of a novel cylindrical arc permanent magnet synchronous motor (CAPMSM) in a large telescope, which requires high positioning accuracy and low torque ripple. A 2D finite element method was used to analyze the cogging torque of the CAPMSM. The CAPMSM can be an alternative for a rotating motor to realize direct drive. A new method is proposed to separate the cogging torque, Tcog, into the torque, Tslot, generated by the slotted effect and the end torque, Tend, generated by the end effect. The average torque and the torque ripple are optimized considering stator center angle, the angle between two adjacent stators and the unequal thickness of a Halbach permanent magnet. The torque ripple decreased from 31.73% to 1.17%, which can satisfy the requirement of tracking accuracy for large telescopes.

Nonreciprocal transmission of electromagnetic waves by three-layer magneto-optical mediums

We investigate the non-reciprocal transmission properties of a three-layer structure filled with magneto–optical medium and normal medium. Based on the transfer matrix method, we deduce the total transmission coefficient for a one-dimensional (1D) structure with anisotropic mediums. When two-side layers with magneto–optical medium loaded in opposite external magnetic field, the time-reversal symmetry of transmission properties will be broken. Our numerical results show that the non-reciprocal transmission properties are influenced by external magnetic fields, incident angle, and thickness of the normal medium layer. Since the non-reciprocal properties can be easily realized and adjusted by the simple structure, such a design has potential applications in integrated circulators and isolators.

Multiobjective design optimization and analysis of magnetic flux distribution for slotless permanent magnet brushless DC motor using evolutionary algorithms

Abstract In this paper, Multi-Objective Optimization (MOO) techniques namely: Weighted Sum Method (WSM), Multi Objective Genetic Algorithm (MOGA) and Niched Pareto Genetic Algorithm (NPGA) are proposed for the design optimization and analysis of magnetic flux distribution for a slotless permanent magnet Brushless DC (BLDC) motor. The sensitivity analysis is carried out to identify the design variables of BLDC motor which influence the objective function. The objective functions are conflicting in nature (maximization of output torque and minimization of total volume and losses), hence, are optimized simultaneously by means of MOO algorithms. The proposed MOOs account for four kinds of design variables namely: rotor radius, stator/ rotor axial length, magnet thickness and winding thickness simultaneously to maximize the output torque and to reduce the total volume and total power loss. The conventional MOO such as WSM gives single pareto optimal solution. However, the proposed MOGA and NPGA algorithms create accurate and well-distributed pareto front set with few function evaluations. The performances of the three MOOs are evaluated and compared using the four performance metrics namely: Hyper Volume (HV), Generational Distance (GD), Inverted Generational Distance (IGD) and Spread. From the comparison, it is observed that NPGA gives better results. Using the design parameter obtained from NPGA, the magnetic flux distribution analysis of the BLDC motor is carried out to analyze variation of flux distribution in the different parts of the motor. The results thus obtained are compared with those obtained through Partial differential equation and single objective GA optimization. The detailed thermal analysis is also carried out to analyze the thermal behavior at different parts of the machine for different working conditions in the continuous operation mode and hence, the results obtained are compared with single objective GA optimization. The advantages of MOOs in the design optimization of slotless permanent magnet BLDC motor are highlighted.

Determination of the Magnetic Permeability, Electrical Conductivity, and Thickness of Ferrite Metallic Plates Using a Multifrequency Electromagnetic Sensing System

In this paper, an inverse method was developed which can, in principle, reconstruct arbitrary permeability, conductivity, thickness, and lift-off with a multi-frequency electromagnetic sensor from inductance spectroscopic measurements. The system fives the error of "Bad character(s) in field Abstract" for no reason. Please refer to manuscript for the full abstract.