Orientation Of Magnetic Domains Research Articles

Ferromagnetism in High Entropy Cantor alloy triggered and tuned by severe plastic deformation

The process of severe plastic deformation (SPD) introduces unique conditions to materials, leading to the emergence of novel properties. This research specifically investigates the observation of deformation-induced ferromagnetism resulting from SPD processing. High-pressure torsion (HPT) is utilized to process both single-phase and nanocomposite high entropy alloys (HEAs). Vibrating sample magnetometry (VSM) confirms that HPT processing triggers the development of ferromagnetic properties. The distribution and alignment of magnetic domains post-SPD treatment are further examined using differential phase contrast scanning transmission electron microscopy (DPC STEM). Atom probe tomography (APT) analysis suggests that this phenomenon stems from the localized enrichment of ferromagnetic elements, particularly Ni, induced by deformation. This observation underscores the ‘cocktail effect’ in HEAs, whereby interactions between different elements has led to this unique magnetic behavior. Additionally, deliberate mechanical mixing of the CoCrFeMnNi alloy with a HfNbTaTiZr HEA, comprising non-ferromagnetic constituents, introduces a large rotational strain that alters the ferromagnetic properties. This mixing facilitates a transition from a random orientation of magnetic domains, as seen in the HPT-processed single CoCrFeMnNi alloy, to a coordinated alignment within the nanocomposite HEA.

Magnetization control of the critical current in a S-(S/F)-S superconducting switch

We show the control of the critical current Ic of a superconductor–superconductor/ferromagnet–superconductor [S-(S/F)-S] type switch by the magnetization state of the F. The inverse proximity effect of a S/F bilayer is used to define the weak link and hence the maximum critical current of the junction. The magnetization of the F lead is set by an external magnetic field. We show that the critical current in zero field depends on the remanent magnetization state via stray-field effects and thereby allows for a post-manufacturing control of the junction's properties, in particular the tunability between a maximal critical current and a full suppression of Ic without applying a persistent magnetic field. We propose a simplified model based on the relative orientation of magnetic domains that explains our findings qualitatively.

Effect of Underlayer Quality on Microstructure, Stoichiometry, and Magnetic Properties of Hexaferrite BaFe12O19 Grown on YSZ(111) by Pulsed Laser Deposition.

We have studied the effect of platinum underlayer for two deposited thicknesses on the microstructure, crystalline quality, morphology, chemical composition, and magnetic properties as well as magnetic domain formation of BaFe12O19 (BaM) grown on YSZ(111) by pulsed laser deposition (PLD). We found that PLD platinum deposited with a thickness of 25 nm cannot withstand the dewetting phenomenon occurring during the subsequent BaM layer growth. A smooth and continuous Pt underlayer that possesses a sharp interface and omits the intermixing between the BaM and substrate was successfully achieved for a deposited Pt film thickness of 75 nm. Independent of the thickness of the deposited Pt layer, the c-axis orientation as well as coercivity Hc and the anisotropy HA fields were significantly improved due to a remarkable improvement of lattice mismatch in comparison with the BaM layer grown without a Pt underlayer on YSZ(111). By applying high-resolution X-ray diffraction, scanning and transmission electron microscopy (SEM/TEM), and atomically resolved scanning TEM imaging combined with energy-dispersive X-ray spectroscopy, as well as atomic and magnetic force microscopy, a comprehensive investigation of both structure and chemical composition of the deposited BaM films and their interfacial regions was performed. This study aimed to correlate the enhancement of the overall magnetic properties and of the local spin magnetic domain orientation with the modification of BaM microstructure and chemical composition at the nanometer scale due to the Pt underlayer. Finally, we attempted to understand the mechanisms that control the magnetic properties of these BaM films in order to be able to tailor them.

Effect of intense x-ray free-electron laser transient gratings on the magnetic domain structure of Tm:YIG

In ferromagnets, domain patterns can be controlled globally using magnetic fields or spin-polarized currents. In contrast, the local control of the magnetization on the nanometer length scale remains challenging. Here, we demonstrate how magnetic domain patterns in a Tm-doped yttrium iron garnet (Tm:YIG) thin film with perpendicular magnetic anisotropy can be permanently and locally imprinted by high intensity photon pulses of a hard x-ray transient grating (XTG). Micromagnetic simulations provide a qualitative understanding of the observed changes in the orientation of magnetic domains in Tm:YIG and XTG-induced changes. The presented results offer a route for the local manipulation of the magnetic state using hard XTG.

Poly(vinyl alcohol)/sodium alginate/magnetite composites: magnetic force microscopy for tracking magnetic domains.

Hydrogels of poly(vinyl alcohol) (PVA)/sodium alginate (SA), and magnetic nanoparticles (MNPs) were prepared by solvent casting in the absence and in the presence of magnets, in order to obtain MNPs distributed randomly (PVA/SA-rMNP) and magnetically oriented MNPs (PVA/SA-gMNP) in the polymer matrix. Atomic force microscopy (AFM) and magnetic force microscopy (MFM) techniques were used to evaluate the topography and to map the distribution of magnetic domains in the polymer matrix, respectively. The tip-surface distance (lift distance) of 50 nm during the MFM analyses facilitated the mapping of magnetic domains because the van der Waals forces were minimized. The magnetic signal stemming from clusters of MNPs were more easily identified than that from isolated MNPs. PVA and SA, PVA/SA, PVA/SA-rMNP, and PVA/SA-gMNP coatings with surface roughness (Ra) values of 3.8 nm, 28.7 nm, and 49.8 nm, respectively, were tested for the proliferation of mouse hippocampal HT-22 cells. While PVA/SA, PVA/SA-rMNP, and PVA/SA-gMNP coatings preserved cell viability >70% in comparison to the control (plastic plate) over 48 h, cell proliferation tended to decrease on surfaces with higher Ra values (PVA/SA-gMNP). These findings showed that the orientation of magnetic domains led to an increase of surface roughness, which decreased the viability of HT-22 cells. Thus, these results might be interesting for situations, where the control of cell proliferation is necessary.

Quantitative study on the effect of stress magnetization of martensite in 304 austenitic stainless steel

Ferromagnetic materials exhibit a stress-magnetic coupling effect, where mechanical and magnetic energy are converted to each other. This effect is known as the effect of stress-magnetization. The effect of stress-magnetization of 304 austenitic stainless steel after the occurrence of martensitic phase transformation to produce ferromagnetic phase is not clear. To clarify the effect of stress-magnetization of alpha'-martensite and its mechanism. A tensile loading test is designed to evaluate the effect. X-ray diffraction (XRD) and Lorentz transmission electron microscopy (LTEM) methods are used to investigate the evolution of microstructures and clarify the mechanism. Furthermore, an analytical expression model is established on the basis of martensitic transformation dynamics and a magneto-mechanical model. The accuracy of the model is validated from perspectives of martensitic transformation, the effect of stress-magnetization of alpha'-martensite, and their combination. Results showed that the effect of stress-magnetization of alpha'-martensite is significant and increases magnetic signal collected by fluxgate sensor. The mechanism is the increase of magnetization of the material due to stress by assimilating the orientation of magnetic domains. The proposed model demonstrates satisfactory accuracy and provides theoretical bases for evaluating mechanical damage in 304 austenitic stainless steel.

A 126 μW Readout Circuit in 65 nm CMOS With Successive Approximation-Based Thresholding for Domain Wall Magnet-Based Random Number Generator

We present a novel readout circuit for a ferro-magnetic Hall cross-bar based random number generator. The random orientation of magnetic domains are result of anomalous Hall-effect. These ferromagnetic Hall cross-bar structures can be integrated with the read out circuit to form a plug and play random number generator. The system can resolve up to 15– $20~\mu \text{V}$ Hall-voltages from Hall probe. Application of current densities around $10^{12} {A/m}^{2}$ through the Ferromagnetic Hall cross-bar produces random Hall-voltage on the output terminals. To amplify the weak Hall-voltages (10– $100~\mu \text{V}$ ) in the presence of DC offsets, a modulation scheme is used to up-convert the signal and a band-pass amplifier is used to amplify the modulated signal. The band-pass amplifier circuit, motivated by neural recording amplifier is designed in 65nm CMOS and consumes $126~\mu \text{W}$ of power from a 1.2 V supply. Further, we present a successive approximation algorithm and its embedded implementation to set the desired threshold for digitizing the amplified Hall-voltage in presence of signal drift. Experimental results show that the resulting system can tolerate drifts in voltage up to $440~\mu \text{V}$ .

Fiber-Optic Current Sensor Based on FBG and Optimized Magnetostrictive Composite

In this letter, we present a compact, open-loop fiber-optic current sensor (FOCS) based on fiber Bragg gratings (FBG) and magnetostrictive composites of Terfenol-D (TD) optimized for enhanced sensitivity and linearity using small concentrations of this alloy. Using magnetic field concentration techniques and orientation of magnetic domains of the composites, a prototype of the proposed FOCS was built with different doping concentrations of TD (10%, 20%, and 40%) and characterized with currents of 15–700 Arms. The proposed FOCS showed a linear response for currents of up to 450 Arms with a linearity error of ±0.55%, a sensitivity of $201~\mu \text{V}$ /A, and 4.8 degrees of phase shift between output and input signals, which are competitive features compared to previous works, since it employs very small amounts of TD (1.5 g max.). The developed prototype also presented a fast response-time to a current transient and a rise time of 1.5 ms, allowing for the proposed FOCS to be applied not only for current sensing, but also to fault detection and monitoring in transmission and distribution lines.

Influence of Crack Size on Stress Evaluation of Ferromagnetic Low Alloy Steel with Metal Magnetic Memory Technology.

Based on the magneto-mechanical effect, the influence of crack size on stress evaluated with metal magnetic memory (MMM) technology was discussed in this paper. Based on equivalent theory, the regular rectangular grooves, with different widths and depths, were precut in the surface of an experimental sample for simulating surface crack, and a three dimensional electrically controlled displacement system was used to collect the Hp(y) signal of the sample under different stresses, and the fracture morphology was observed by using scanning electron microscopy (SEM). The results show that the influence of detection line on Hp(y) signal can be ignored; as stress increases, the Hp(y) signal turns counterclockwise around zero-crossing point and its mutation, corresponding to the location of groove, becomes distinct gradually. When groove depth is constant, the magnetic intensity gradient changes in the form of quadratic polynomial as groove width increases, and when the groove width is the same, the magnetic intensity gradient is a linear function of groove depth. When stress reaches the yield strength of the material, the magnetic intensity gradient decreases gradually as stress increases further, and the orientation of magnetic domain is seen as the main reason for that result. At last, the experimental results are discussed based on the piezomagnetic effect and leakage magnetic field theory of finite depth slit model, and the change of magnetic domain orientation is considered to be the main reason.

A scanning reflection X-ray microscope for magnetic imaging in the EUV range.

The mechanical setup of a novel scanning reflection X-ray microscope is presented. It is based on zone plate optics optimized for reflection mode in the EUV spectral range. The microscope can operate at synchrotron radiation beamlines as well as at laboratory-based plasma light sources. In contrast to established X-ray transmission microscopes that use thin foil samples, the new microscope design presented here allows the investigation of any type of bulk materials. Importantly, this permits the investigation of magnetic materials by employing experimental techniques based on X-ray magnetic circular dichroism, X-ray linear magnetic dichroism or the transversal magneto-optical Kerr effect (T-MOKE). The reliable functionality of the new microscope design has been demonstrated by T-MOKE microscopy spectra of Fe/Cr-wedge/Fe trilayer samples. The spectra were recorded at various photon energies across the Fe 3p edge revealing the orientation of magnetic domains in the sample.

Magnetic domains characterization of clusters of magnetite nanoparticles

In this paper, magnetite (Fe3O4) powders which were obtained by the emulsion method are analyzed to ascertain the structure and mechanism formation of domains in clusters of Fe3O4 nanoparticles. Magnetic force microscopy (MFM) occupies a special niche in the array of techniques which are currently available for imaging magnetic structures of magnetic nanomaterials, yielding high resolution under ambient conditions. The use of MFM in dynamic lift-mode to detect probe–sample interactions from Fe3O4 nanoparticles is reported here to detect and identify the magnetic domains characterization of nanoparticles. The experimental results showed orientation of magnetic domains in the clustering nanoparticles. Finally, an analysis of repulsion and attraction in magnetic field and direction changes of domains formed by magnetite nanoparticles were done. This approach for probing magnetic responses on nanoscale magnetic domains can be further extended to the analysis of local physical features.

Tailoring ferroic domains by introducing internal stress: Fe81Ga19 magnetostrictive alloy as an example

Ferroic materials, including ferromagnets, ferroelectrics, and ferroelastics, can output strain via domain reversal stimulated by external fields. However, domains with multiple orientations generally form in ferroic materials, resulting in a small value of output strain. Tailoring the preferential orientation of ferroic domains is important for realizing large strain. In this work, taking Fe81Ga19 magnetostrictive alloys as an example, the preferential orientation of magnetic domains was realized by introducing unidirectional internal stress during single crystal growth. As a result, a large magnetostriction of 300 ppm which was close to the theoretical value of the Fe81Ga19 alloy was obtained from the single crystal without the application of bias pre-stress. After 106 magnetization cycles, the magnetostriction was unchanged, exhibiting high stability. This work may supply an effective approach to tailor ferroic domains towards large strain and some other physical effects in ferroic materials.

3D-printing polymer-based permanent magnets

Production of permanent magnets is a complex process that implies very specific machinery able to perform very specific actions. Even though this problem has been approached by extrusion-based three-dimensional printing techniques, the resulting parts either have not been fully characterized or present low-resolution outputs. In this study we use the stereolithography three-dimensional printing technique to address this problem and demonstrate that it is possible to develop high-resolution polymer-based permanent magnets. We report an in-depth magnetic characterization of the produced materials, including magnetization of saturation, coercivity, magnetic relative permeability, magnetic behaviour, type of interaction between particles, and magnetic domain orientation. We have further demonstrated that this orientation can be re-arranged. Obtaining contrasting properties of the developed materials opens the possibility of developing personalized, high-resolution devices that can be used in a wide range of fields such as micro-robotics, biotechnology, biomedicine, and medical science among many others.

Effect of Deformation on the Magnetic Domain Orientation of Rapidly Solidified Nd–Fe–B Powders Using Pulsed Current Assisted Sintering

Effect of Deformation on the Magnetic Domain Orientation of Rapidly Solidified Nd–Fe–B Powders Using Pulsed Current Assisted Sintering

Hydrogenation-induced reversible spin reorientation transition in Co50Pd50 alloy thin films

Abstract Because of the Pd-catalyzed hydrogen dissociation and absorption, magnetic Pd-alloys provide a model system for the investigation of the critical hydrogenation effect on magnetism. In this study, Co 50 Pd 50 (CoPd) alloy thin films were fabricated by e-beam-heated co-evaporation on Al 2 O 3 (0001) substrates. These films exhibited a thickness-dependent spin reorientation transition (SRT) from perpendicular direction to in-plane direction with increase of thickness. For 10-30 nm-thick CoPd alloy films with perpendicular magnetic anisotropy (PMA), hydrogenation triggered a SRT to an in-plane anisotropy. The reversibility of SRT was demonstrated by cyclicly changing the hydrogen gas pressure. Furthermore, hydrogenation-induced SRT randomized the magnetic domain orientation. The surface morphology of the CoPd thin films was composed of nanoclusters, which may play a crucial role in hydrogen dissociation and affect PMA. In comparison with a bare CoPd film, a stronger PMA and a less pronounced hydrogenation-induced SRT were observed in a Pd-capped CoPd film. These observations suggest that the hydrogen content in CoPd alloy films can drastically and reversibly modify PMA, inferring the possible hydrogenation-induced charge transfer and modulation of electronic structure in CoPd.

Shape-dependent magnetic properties of Co nanostructure arrays synthesized by pulsed laser melting

One dimensional (1D) magnetic nanowires show unique magnetic behaviors, such as large coercivity and high remanence, in comparison to the bulk and thin film materials. Here, planar arrays of Co nanowires, nanorods and nanoparticles were fabricated from thin Co films by a nanosecond pulsed laser interference irradiation technique. Magnetic force microscopy (MFM) and surface magneto-optic Kerr effect (SMOKE) techniques were used to study the individual and average magnetic properties of the nanostructures. Magnetic domain orientation was found to depend on the in-plane aspect ratio of the nanostructure. The magnetic orientation was out-of-plane for in-plane aspect ratio ranging from 1 to 1.4 and transitioned to an in-plane orientation for aspect ratios greater than 1.4 (such as in nanorods and nanowires). Our results also showed that polycrystalline Co nanowires showed much higher coercivity and remanence as compared to bulk and thin film materials, as well as shapes with smaller aspect ratio. This result was attributed mainly to the shape anisotropy. This study demonstrated that nanosecond pulsed laser synthesis is capable of fabricating various nanostructures in a simple, robust and rapid manner and SMOKE is a reliable technique to rapidly characterize such magnetic nanostructures.

Structure and magnetic properties of electrodeposited Ni87.3Fe11.3W1.4 alloy

A dark gray nanostructured coating of an alloy composed of 87.3wt.% Ni, 11.3wt.% Fe and 1.4wt.% W (Ni87.3Fe11.3W1.4) was electrodeposited from an ammonia citrate bath on a titanium cathode at a current density of 500mAcm−2.A cathodic polarization curve was recorded and dependence of the current efficiency of alloy deposition on current density was determined. Partial polarization curves for alloy deposition and hydrogen evolution were also measured. Alloy deposition at current densities of up to 300mAcm−2 is an activation-controlled process which turns into a diffusion-controlled process at higher current densities. At potentials more positive than −960mV, hydrogen is evolved from NH4+ and (HCit)3− ions (where (HCit)3− denotes triply deprotonated citric acid, C6H5O73−). At potentials more negative than −960mV, hydrogen evolution from water is the dominating reaction.SEM images show that the surface of the deposit obtained at 500mAcm−2 has a globular structure containing a large number of craters, mostly located between the globules.XRD analysis revealed that the alloy contains an amorphous matrix with embedded nanocrystals of the FCC-structured solid solution of Fe and W in Ni with a mean particle size of 8.8nm. The deposit has a high internal microstrain value and a high density of chaotically distributed dislocations.Heating and milling the alloy cause structural changes involving changes in the magnetic properties of the alloy. Structural relaxation takes place in the temperature interval of 80°C tо 420°C. In this temperature range, magnetization of both as-deposited and milled alloy samples increases with increasing temperature, reaching maximum at a certain temperature, but decreases thereafter with further heating. During structural relaxation, short-term structural arrangement facilitates the expansion and orientation of magnetic domains, leading to increased magnetization of the alloy. The abrupt decline in magnetization at higher temperatures is the result of a heat-induced change in magnetic domain orientation.Annealing the alloy at temperatures above 420°C causes amorphous phase crystallization and growth of crystal grains of the FCC-structured solid solution of Fe and W in Ni, as well as a simultaneous decrease in internal microstrain and mean density of chaotically distributed dislocations. The same structural changes, somewhat lower in intensity, are also caused by alloy milling. The new state of the microstructure achieved through annealing and milling is best illustrated by the mean crystal size. The increase in mean crystal size results in a shift of the Curie temperature towards lower temperatures, whereas magnetization increases at first, reaching maximum at a certain mean crystal size, but decreases, thereafter, with a further increase in mean crystal size.

Magnetotactic Artificial Self-Propelled Nanojets

Self-propelled catalytic bubble-ejecting nanotubes (nanojets) are expected to perform a variety of autonomous tasks. Herein, we will show that with the introduction of a Ni segment into the Au/Ni/Pt nanotube design followed by consequent magnetization a permanent change in the magnetic domain orientation of the Ni segment can be induced. Consequently, this results in the presence of a permanent magnet within the nanojet with its north/south domains oriented along the tube axis. Such a magnetized nanojet orients itself according to the external magnetic field and propels itself toward or away from the source of the magnetic field depending on its orientation. This behavior is similar to that of the magnetotactic bacteria. The ability to sense the magnetic field is expected to have a strong impact on future applications of autonomous self-propelled nanojets.

Optimization of Magnetooptic Device by Low Switching Field Domains

This paper expounds on the optimization of magnetooptic devices using preferential domains that switch at low field strengths. In particular, an all-optical switch for transparent networks based on the Mach-Zehnder interferometer configuration is examined in detail. The switch utilizes bismuth-substituted iron garnets with a specific composition of (Bi1.1Tb1.9)(Fe4.25Ga0.75)O12 as Faraday rotators. It is proposed that switch figures of merit can be improved by preferentially choosing domains which align with applied fields at field strengths much lower than required by the bulk material. Measurement of magnetic domain orientation in the material and Faraday rotation within domains is reported. The domain behavior in low magnetic fields is also investigated to achieve a switch with lower switching times and higher extinction ratios.

Magnetic field-induced off-resonance third-order optical nonlinearity of iron oxide nanoparticles incorporated mesoporous silica thin films during heat treatment

Highly dispersed and uniform Fe(2)O(3) nanoparticles (NPs) have been incorporated into the pore channels of SBA-15 mesoporous silica thin films (MSTFs). And such Fe(2)O(3) NPs incorporated MSTFs did not show detectable nonlinear optical (NLO) signals at off-resonance wavelength 1064 nm by Z-scan technique. However after a vacuum heat treatment at 800 degrees C for 1 h under 6 T magnetic field, the Fe(2)O(3) NPs incorporated MSTFs with very low Fe content (0.8 approximately 1.5 at.%) presented distinctive NLO signals with chi(3) value in an order of 10(-10) esu. We proposed the physical reason for the NLO property generation to be the magnetic domain orientation of the iron oxide NPs incorporated within the pore channels of the MSTFs by the magnetic field heat treatment.