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A fault current limiter including: a ferromagnetic circuit formed from a ferromagnetic material and including at least a first limb, and a second limb; a saturation mechanism surrounding a limb for magnetically saturating the ferromagnetic material; a phase coil wound around a second limb; a dielectric fluid surrounding the phase coil; a gaseous atmosphere surrounding the saturation mechanism.
Multiferroic composites and heterostructures comprising ferroelectric and ferromagnetic materials exhibit room-temperature magnetoelectric (ME) effects greatly exceeding those of single-phase magnetoelectrics known to date. Since these effects are mediated by the interfacial coupling between ferroic constituents, the ME responses may be enhanced by increasing the density of interfaces and improving their quality. A promising material system providing these features is a ferroelectric-ferromagnetic multilayer with epitaxial interfaces. In this paper, we describe theoretically the strain-mediated direct ME effect exhibited by free-standing multilayers composed of single-crystalline ferroelectric nanolayers interleaved by conducting ferromagnetic slabs. Using a nonlinear thermodynamic approach allowing for specific mechanical boundary conditions of the problem, we first calculate the polarization states and dielectric properties of ferroelectric nanolayers in dependence on the lattice mismatch between ferroic constituents and their volume fractions. In these calculations, the ferromagnetic component is described by a model which combines linear elastic behavior with magnetic-field-dependent lattice parameters. Then the quasistatic ME polarization and voltage coefficients are evaluated using the theoretical strain sensitivity of ferroelectric polarization and measured effective piezomagnetic coefficients of ferromagnets. For Pb(Zr₀.₅Ti₀.₅)O₃-FeGaB and BaTiO₃-FeGaB multilayers, the ME coefficients are calculated numerically as a function of the FeGaB volume fraction and used to evaluate the output charge and voltage signals. It is shown that the multilayer geometry of a ferroelectric-ferromagnetic nanocomposite opens the way for a drastic enhancement of the output charge signal. This feature makes biferroic multilayers advantageous for the development of ultrasensitive magnetic-field sensors for technical and biomedical applications.
Alternating cycles of isothermal magnetization and adiabatic demagnetization applied to a magnetocaloric material can drive refrigeration in very much the same manner as cycles of gas compression and expansion. The material property of interest in finding candidate magnetocaloric materials is ΔS M , their gravimetric entropy change upon application of a magnetic field under isothermal conditions. There is, however, no general method for screening materials for such an entropy change without actually performing the relevant, time- and effort-intensive magnetic measurements. Here we propose a simple computational proxy based on performing nonmagnetic and magnetic density functional theory calculations on magnetic materials. This proxy, which we term the magnetic deformation Σ M , is a measure of how much the unit cell deforms comparing with the relaxed structures with and without the inclusion of spin polarization. Σ M appears to correlate very well with experimentally measured magnetic entropy change values. Here, the proxy has been tested against 33 ferromagnetic materials with known ΔS M , including nine materials newly measured for this study. It has then been used to screen 134 ferromagnetic materials for which the magnetic entropy has not yet been reported, identifying 30 compounds as being promising for further study. As a demonstration of the effectiveness of our approach, we have prepared one of these compounds and measured its isothermal entropy change. MnCoP, with a T C of 575 K, shows a maximal ΔS M of –6.0 J kg –1 K –1 for an H = 5 T applied field.
We studied the magnetization of zinc blende Mn{sub 1-x}Cr{sub x}S films embedded between diamagnetic ZnSe layers grown by molecular beam epitaxy with chromium mole fractions x {<=} 0.7. These ternary semiconductors exhibit an increasing ferromagnetic contribution with increasing x caused by competing antiferromagnetic and ferromagnetic coupling. As a result, whereas MnS in the zinc blende phase is a pure antiferromagnet, it was found that with increasing x zinc blende Mn{sub 1-x}Cr{sub x}S became a ferromagnet. The ferromagnetic phase transition dominates in case of x greater than about 0.5. Hence, we conclude that metastable zinc blende CrS will be a ferromagnetic material with half-metallic character in contrast to the analogous stable NiAs-structure which exhibits an antiferromagnetic phase transition.
This work proposes to use magnetic material as the substrate of planar antennas to overcome the platform effect caused by the conducting ground plane. The upper bound of the radiation efficiency of an electric-current-driven low-profile antenna is theoretically derived, which is inversely proportional to the Gilbert damping factor of the magnetic material. Meanwhile, the improvement of radiation due to the use of magnetic material is demonstrated by a three-dimensional (3D) multiphysics and multiscale time-domain model. The simulation results match the theoretical derivation, showing 25% radiation efficiency from a planar antenna backed by a FeGaB thin film with 2.56 m thickness. Furthermore, for conductive ferromagnetic materials, it is shown that the eddy current loss can be well suppressed by laminating the thin film into multiple layers. Here, the radiation efficiency of the modeled antenna with a conductive ferromagnetic substrate is improved from 2.2% to 11.8% by dividing the substrate into 10 layers, with a ferromagnetic material fill factor of 93%.
Here in this work, the suitability of magnetic Barkhausen noise as an intrinsic fingerprint of ferromagnetic components is determined. This technique has potential for this application because it is based inherently on the near surface microstructural features of ferromagnetic materials. All materials typically display some variation in their microstructure simply as a result of the manufacturing process (rolling, heat treating, welding, grinding), thus providing the potential that Barkhausen noise measurements between nominally similar components will be unique. In this work, we demonstrate that Barkhausen noise measurements are both repeatable in time for a single sample made from a ferromagnetic material, and unique across a number of instances of nominally similar samples. The results of this work have profound implications in a variety of applications in forensics and physical security. For example, consider the fabrication of the next generation of tamper-evident containers and devices using conventional processes for steel. In addition, since Barkhausen noise is sensitive to changes in microstructures due to grinding and welding, these measurements can be used to detect clandestine repairs and tampering. Finally, because the method inherently results in a time series measurement at each point on a sample, it is expected to have far higher dimensionality than physically similar eddy current measurement. However, the higher dimensionality of Barkhausen measurements suggest that they should be harder to counterfeit than eddy current measurements.
A positive-feedback mean-field modification of the classical Brillouin magnetization theory provides an explanation of the apparent persistence of the spontaneous magnetization beyond the conventional Curie temperature—the little understood “tail” phenomenon that occurs in many ferromagnetic materials. The classical theory is unable to resolve this apparent anomaly. The modified theory incorporates the temperature-dependent quantum-scale hysteretic and mesoscopic domain-scale anhysteretic magnetization processes and includes the effects of demagnetizing and exchange fields. It is found that the thermal behavior of the reversible and irreversible segments of the hysteresis loops, as predicted by the theory, is a key to the presence or absence of the “tails.” The theory, which permits arbitrary values of the quantum spin number J, generally provides a quantitative agreement with the thermal variations of both the spontaneous magnetization and the shape of the hysteresis loop.
This final report summarizes the research findings of the current project. This project is a collaboration between New Mexico State University (NMSU) as a lead (Recipient) and Arizona State University (ASU) as a Co-Recipient. Tubular structures are common components of boilers and heat exchangers in power plants. Over time, these components may suffer corrosion, cracks, and stress-corrosion cracks in either the body or the welded connections. A single tube leakage can cause an outage of several weeks. Regular inspection is a key safety factor when ensuring that power plants are maintained in reliable, operational condition. This inspection, however, is challenging, time-consuming, and in many cases impossible due to accessibility issues and safety concerns. Recent developments in robotic-based inspection can offer a great solution. Hard-to-reach places can be inspected without overhauling the unit, saving time and cost. Although several robots have been designed and implemented successfully for inspecting power plant components, in particular tubular structures, their mobility and flexibility are limited. Most of these robots use wheels for mobility which reduces their maneuverability of these robots. Moreover, they usually use magnets to attach to tubes which will not work on tubes with non-ferromagnetic materials. These robots usually carry measurement tools for a particular non-destructive testing (NDT) method such as ultrasound testing (UT) that requires a couplant to perform a point-by-point (scanning) inspection of the tubular structure. In this project, we developed a versatile lizard-inspired tube inspector (LTI) robot with embedded inspection sensing components for tube inspection which removes the need for point-by-point scanning of tube surface for crack and corrosion detection. Inspired by a “lizard”, the novelty of the current project is the integration of couplant-free ultrasound sensing and transmission, advanced data-driven defect detection and imaging, and friction-based mechanical mobility components in a single robot to eliminate a need for smooth surfaces and simple geometry for mobility and scanning. The LTI robot could replace the wheel-based approach with friction-based mobility to significantly increase the flexibility and maneuverability of the robot. The LTI robot can get into a power plant unit, such as a boiler, from a small area allowing it to access a component of interest for inspection (e.g., move on OD, curved and flat surfaces, non-ferromagnetic or ferromagnetic materials, and tubes with rough surfaces and complex geometries). Additionally, an advanced data-driven method using ultrasound data was pioneered to allow the robot to detect defects in the entire area between the robot’s multi-functional mobility system (grippers). Integrating a couplant-free ultrasound sensing in the robot’s grippers as well as using advanced data-driven methods allowed the LTI to detect defects in the entire cross-section of a tube using its grippers when stationary and when mobile.
The understanding of the magnetovolume effect lacks explicit consideration of spin-lattice coupling at the atomic level, despite abundant theoretical and experimental studies throughout the years. This research gap is filled by the recently developed spin-lattice dynamics technique implemented in this study, which investigates the magnetovolume effect of isotropic body-centered-cubic (BCC) iron, a topic that has previously been subject to macroscopic analysis only. This approach demonstrates the magnetic anomaly followed by the volumetric changes associated with the effect, each characterized by the corresponding field-induced inflection temperature. The temperature of the heat capacity peaks is useful in determining the temperature for retarding the atomic volume increase. Moreover, this work shows the correlation between the effects of temperature and field strength in determining the equilibrium atomic volume of a ferromagnetic material under a magnetic field.
In past work a measurement system for the in-line acquisition of material properties was developed at IVP. This system is based on the non-destructive eddy-current principle. Using this system, a 100% control of material properties of the processed material is possible. The system can be used for ferromagnetic materials like standard steels as well as paramagnetic materials like Aluminum and stainless steel. Used as an in-line measurement system, it can be configured as a stand-alone system to control material properties and sort out inapplicable material or as part of a control system of the forming process. In both cases, the acquired data can be used as input data for numerical simulations, e.g. stochastic simulations based on real world data.
Ferrites (garnets) are a model object of study and a promising material to be used in magneto-optical devices for data recording and processing and IR modulators. Due to the narrow ferromagnetic resonance line, optical transparency, and high elastic Q factor of ferrite single crystals, they are promising for solid-state microwave, optoelectronic, and computation devices. To ensure the optimal application of ferromagnetic materials, it is necessary to complete the following important task: develop a certification for samples with allowance for the degree of their imperfection caused by the deviation of crystals with garnet structure from stoichiometry, the competitive incorporation of process and dominant impurities, oxygen vacancies, etc.
Graphical abstract: - Highlights: • Calculating the crystallinity percentage and percentage of phases presented in Co–Au core–shell nanoparticles. • Magnetic properties of four groups nanogarin: 5, 10, 15, 20 nm. • Single domain ferromagnetic materials with high coercivity at room temperature. • Intrinsic blocking temperature measured in zero field cooled-warmed (ZFC-W). - Abstract: Size-controlled cobalt–gold core–shell nanoparticles were synthesized via the reverse-micelle microemulsion method. In order to control the size of the nanoparticles, the nucleation and growth process were performed within a confined space by adjusting the water to surfactant ratio of reverse micelles solution during synthesis. The crystallinity percentage and percentage of phases presented in Co–Au core–shell nanoparticles were calculated using X-ray diffraction data. The results from transmission electron microscopy provide direct evidence for core–shell structure nanomaterials. Magnetic properties of the samples were investigated using a vibrating sample magnetometer. The as-prepared samples showed significant coercivity at room temperature. The intrinsic blocking temperature was experimentally deduced from zero-field-cooled warmed (ZFC-W) curves by a simple method without employing an external magnetic field. The B-field dependence temperature data of Co–Au nanoparticles exhibited an intrinsic blocking temperature at 45 K. Annealing these samples at 400 °C caused an increase in particle size, crystallinity percentage and further enhanced their magnetic properties.
Mechanically exfoliated two-dimensional ferromagnetic materials (2D FMs) possess long-range ferromagnetic order and topologically nontrivial skyrmions in few layers. However, because of the dimensionality effect, such few-layer systems usually exhibit much lower Curie temperature (T C ) compared to their bulk counterparts. It is therefore of great interest to explore effective approaches to enhance their T C , particularly in wafer-scale for practical applications. Here, we report an interfacial proximity-induced high-T C 2D FM Fe 3 GeTe 2 (FGT) via A-type antiferromagnetic material CrSb (CS) which strongly couples to FGT. A superlattice structure of (FGT/CS) n , where n stands for the period of FGT/CS heterostructure, has been successfully produced with sharp interfaces by molecular-beam epitaxy on 2-inch wafers. By performing elemental specific X-ray magnetic circular dichroism (XMCD) measurements, we have unequivocally discovered that T C of 4-layer Fe 3 GeTe 2 can be significantly enhanced from 140 K to 230 K because of the interfacial ferromagnetic coupling. Meanwhile, an inverse proximity effect occurs in the FGT/CS interface, driving the interfacial antiferromagnetic CrSb into a ferrimagnetic state as evidenced by double-switching behavior in hysteresis loops and the XMCD spectra. Density functional theory calculations show that the Fe-Te/Cr-Sb interface is strongly FM coupled and doping of the spin-polarized electrons by the interfacial Cr layer gives rise to the T C enhancement of the Fe 3 GeTe 2 films, in accordance with our XMCD measurements. Strikingly, by introducing rich Fe in a 4-layer FGT/CS superlattice, T C can be further enhanced to near room temperature. Our results provide a feasible approach for enhancing the magnetic order of few-layer 2D FMs in wafer-scale and render opportunities for realizing realistic ultra-thin spintronic devices.
Ultrahigh frequencies (UHF) have applications in signal and power electronics to minimize product sizes, increase production quantity and lower manufacturing cost. In the UHF range of 300 MHz to 3 GHz, ferrimagnetic iron oxides (ferrites) are especially useful because they combine the properties of a magnetic material with that of an electrical insulator. Ferrites have much higher electrical resistivity than metallic ferromagnetic materials, resulting in minimization of the eddy current losses, and total penetration of the electromagnetic (EM) field. Hence ferrites are frequently applied as circuit elements, magnetic storage media like read/write heads, phase shifters and Faraday rotators. The electromagnetic properties of ferrites are affected by operating conditions such as field strength, temperature and frequency. The spinel system Zn{sub x}Co{sub 1-x}Fe{sub 2}O{sub 4} (x=0.0, 0.25, 0.50 and 0.75) has been prepared by the standard solid state sintering method. X-ray and neutron powder diffraction measurements were performed at room temperature. Neutron diffraction data analysis confirms the cubic symmetry corresponding to the space group Fd3m. The distribution of three cations Zn{sup 2+}, Co{sup 2+} and Fe{sup 3+} over the spinel lattice and other crystallographic parameters like lattice constant, oxygen position parameter, overall temperature factor and occupancies of different ions in different lattice sites for the samples have been determined from the analysis of neutron diffraction data. The lattice constant increases with increasing Zn content in the system. The magnetic structure was found to be ferrimagnetic for the samples with x≤0.50. Magnetization measurements show that with the increase of Zn content in the system the value of saturation magnetization first increases and then decreases. The variation of the magnetic moment with Zn substitution has been discussed in terms of the distribution of magnetic and non-magnetic ions over the A and B sub-lattices and their exchange coupling.
A comparative experimental study of the magnetic properties of CoPt{sub 3} and CoPt{sub 3}/Au nanoparticles as well as a detailed study of the structural properties of the samples by X-ray diffraction, Transmission electron microscopy, and vibrating sample magnetometer is presented in this work. In addition, the effect of particle size on the structure and magnetic properties of nanoparticles prepared by microemulsion is studied. The correlation between particle size, crystallinity, and magnetization was studied as well. CoPt nanoparticles have been studied intensively over the last decade because of their increased magnetic anisotropy in the ordered phase that can be interesting for high density magnetic recording. A significant high coercivity for as-prepared CoPt{sub 3} and CoPt{sub 3}-Au nanoparticles was obtained at room temperature and enhanced after annealing. The focused aim of our study is to obtain high coercivity at room temperature that follows the Curie-Weiss law. This indicates an interacting system in which the nanoparticles behave like single domain ferromagnetic materials in the particle size range of 8 to 35 nm. In addition, the interaction increases by cooling the samples to low temperature around 15 K. Temperature dependence 1/M graph was obtained to investigate the behavior of nanoparticles at low temperature and shows the best fit with Curie-Weis mode.
We investigate spin transport and accumulation in n{sup +}-Si using Heusler compound Co{sub 2}FeSi/MgO/Si on insulator (SOI) devices. The magnitudes of the non-local four- and three-terminal Hanle effect signals when using Heusler compound Co{sub 2}FeSi/MgO/SOI devices are larger than when using CoFe/MgO/SOI devices, whereas the preparation methods of MgO layers on SOI are exactly same in both devices. Different bias voltage dependencies on the magnitude of spin accumulation signals are also observed between these devices. Especially, Co{sub 2}FeSi/MgO/SOI devices show large spin accumulation signals compared with CoFe/MgO/SOI devices in the low bias voltage region less than ∼1000 mV in which the increase of the spin polarization is expected from the estimation of the density of states in Heusler compound Co{sub 2}FeSi and CoFe under spin extraction conditions. These results indicate that the species of ferromagnetic material definitely affects the magnitude and behavior of the spin signals. The use of highly polarized ferromagnets such as Heusler compounds would be important for improving the spin polarization and the magnitude of spin signals through Si channels.
A new type of epitaxial ferromagnetic nitride (Ni{sub 3} Fe N = permalloy nitride = 'PyN') compound films were grown on Al{sub 2}O{sub 3}(1120) substrates using reactive triode magnetron sputtering. The results of electron back-scattering diffraction and x-ray diffraction techniques indicate a high quality epitaxial crystalline structure with growth normal of (100). Magnetization measurements of epitaxial PyN films revealed several unique results. (1) A textbook square hysteresis loop that suggest existence of single magnetic domain in these films. (2) A coercive field is tunable from a few mOe up to a few Oe by changing the film thickness. (3) A magnetization that switches (rotate) over a very small field range of {delta}H{sub C} {<=} 0.05 Oe, independent of the film thickness. This small {delta}H indicates a very large resistive sensitivity ({delta}R/{delta}H) of the epitaxial PyN. (4) The epitaxial PyN thermal cycling through several cycles between '2 and 800 K' (-271 Degree-Sign C to +527 Degree-Sign C) shows much less degradation only about 2-5% compared to 40% degradation of a simple Py film. Four-probe transport measurements give an anisotropic magnetoresistance of Almost-Equal-To 6%, sufficiently higher than other known ferromagnetic materials. These interesting properties are ideal for a variety of spintronic devices and magnetic sensors.
Magnetic domains and the walls between are the subject of great interest because of the role they play in determining the electrical properties of ferromagnetic materials and as a means of manipulating electron spin in spintronic devices. However, much less attention has been paid to these effects in antiferromagnets, primarily because there is less awareness of their existence in antiferromagnets, and in addition they are hard to probe since they exhibit no net magnetic moment. In this paper, we discuss the electrical properties of chromium, which is the only elemental antiferromagnet and how they depend on the subtle arrangement of the antiferromagnetically ordered spins. X-ray measurement of the modulation wavevector Q of the incommensurate antiferromagnetic spin-density wave shows thermal hysteresis, with the corresponding wavelength being larger during cooling than during warming. The thermal hysteresis in the Q vector is accompanied with a thermal hysteresis in both the longitudinal and Hall resistivity. During cooling, we measure a larger longitudinal and Hall resistivity compared with when warming, which indicates that a larger wavelength at a given temperature corresponds to a smaller carrier density or equivalently a larger antiferromagnetic ordering parameter compared to a smaller wavelength. This shows that the arrangement of the antiferromagnetic spins directly influences the transport properties. In thin films, the sign of the thermal hysteresis for Q is the same as in thick films, but a distinct aspect is that Q is quantized.