Magnetic Microstructure Research Articles

Understanding the role of Cu element in nanocrystalline hot deformed Nd-Fe-B magnets

Alloying with Cu element has long been established as a means of improving the performance of sintered NdFeB magnets, but its effect on nanocrystalline hot-deformed magnets has not been thoroughly discussed yet. In this study, we conducted a systematic comparison of the microstructure and magnetic properties of nanocrystalline Nd14Fe80B6 and Nd14Fe79B6Cu magnets. The results showed that the introduction of Cu significantly enhances the coercivity of both melt-spun and hot-deformed Nd-Fe-B magnets, owing to the improved magnetically decoupling between neighboring Nd2Fe14B matrix grains by the enrichment of Cu at Nd-rich grain boundary (GB) layer. Despite the magnetic dilution resulting from the introduction of non-magnetic Cu, a significant improvement of remanence from 11.0 kGs to 12.2 kGs is observed in the hot-deformed Nd-Fe-B magnet with 1 at.% Cu addition. The enhancement is attributed to the improved orientation of the Cu-added magnet, as evidenced by the preferential grain alignment from microstructural characterization. The addition of trace Cu changes the properties of the Nd-rich GB phase, lowering its melting point and improving the hot-workability of the Nd-Fe-B magnet during the hot-deformation process. Overall, this study clarifies the positive role of Cu in nanocrystalline Nd-Fe-B magnets and highlights its importance for grain alignment during hot-deformation processing.

Magnetoresistance Features at the Magnetic Field-Induced Phase Transition in FeRh Thin Films

The causes of the appearance of first-order magnetic phase transitions remain a mystery. FeRh alloy is a classical material where a first-order magnetic phase transition occurs. The authors of this article studied the phase transition from the antiferromagnetic state to the ferromagnetic state in FeRh alloy. Comparison of the magnetometry and transport properties results allowed us to determine a number of differences in the mechanisms of the phase evolution during magnetic field and temperature induced transition. This article notes the priority of the rearrangement of the micromagnetic structure of the ferromagnetic phase as a result of the induction of a phase transition by a magnetic field. The main feature of the magnetic field induced phase transition compared to the temperature induced one is the change in the micromagnetic structure of the ferromagnetic phase. The growth of a ferromagnetic phase with less scattering fields leads to asymmetric behavior when a phase transition is induced near the metastable state. We also focused on the importance of taking into account the effect of magnetostriction when analyzing the evolution of the phase transition, which leads to the irreversibility of the phase transition near a zero magnetic field.

Effect of к-carrageenan on saltiness perception and texture characteristic related to salt release in low-salt surimi

The purpose of this study was to investigate the effect of Kappa (к)-carrageenan on texture and perception of saltiness of low salt surimi. The low-field nuclear magnetic resonance (LF-NMR) and microstructure results showed that к-carrageenan could promote the formation of more immobilized water in low salt surimi gel, change its matrix structure, and lead to the uneven spatial distribution of sodium, thus enhancing saltiness perception. The rheological properties of surimi showed that к-carrageenan could increase the network strength of low salt surimi gel and improve its thermostability. Furthermore, the low salt surimi gel added with к-carrageenan has lower cooking loss, higher water holding capacity (WHC), gel strength and improved texture properties. Therefore, к-carrageenan has the effects of improving the quality and increasing salt perception of surimi gel. This study provides a new method for reducing salt consumption in food industry.

Theoretical model of magnetoacoustic emission considering the microstructure of ferromagnetic material

Magnetoacoustic emission (MAE) holds great promise for evaluating the mechanical properties of ferromagnetic materials. To refine the problems of the current theoretical and numerical models of MAE, a theoretical MAE model that considers the microscopic dependence of the hysteresis properties is proposed in this paper. The microstructure (dislocation density and grain size) and the correlation of MAE jumps are considered and incorporated into the model. Then, the influences of magnetization parameters and microstructure parameters on the envelope of the MAE signal are analyzed by the proposed theoretical model. The proposed theoretical model is then fully evaluated by simulations and experiments. The MAE experiments are conducted on ferromagnetic specimens with different hardnesses, and the MAE signals with different hardnesses are simulated by inverting the basic parameters of the MAE model with the genetic algorithm. Further, the crucial hysteresis parameters of the specimens are calculated using the results of microscopic measurements and the calculated parameters agree well with inversion results from experimental signals. The results demonstrate that the proposed theoretical model is valid for the MAE signal simulation. The trends of different hardnesses can be predicted by the MAE simulation signals. Moreover, the model can be used for theoretical analysis of the microscopic dependence of the MAE signal.

Phase Field Simulations of Microstructures in Porous Ferromagnetic Shape Memory Alloy Ni2MnGa

The magnetic domain structures and martensite microstructures of porous Ni2MnGa Heusler alloys with various circle-shaped and ellipse-shaped pores were systematically studied by the phase field method. The magnetization curves and magnetic field-induced strains (MFIS) at the external field were determined. A mesoscopic mechanism was proposed for simulation to reveal the influence of the pores on the microstructures and the MFIS of porous magnetic shape memory alloy. The stress concentration effect and the recovery strain of the porous alloy are studied. The results indicate the MFIS value increases when ellipse-shaped pores elongate along the twin boundary. The effects of porosity and pore size on MFIS for porous Ni-Mn-Ga alloys with randomly distributed pores were also explored. The present study is of guiding significance for understanding the role played by pores on the MFIS and may provide a possible way to adjust the functional properties of ferromagnetic shape memory alloys.

Improvements in properties of NdFeB magnets obtained via magnetron sputtering and thermal diffusion

The grain boundary diffusion process (GBDP) of Dy and DyAl on sintered NdFeB magnets was conducted via magnetron-sputtering deposition of Dy and DyAl films to enhance coercivity (Hcj). The magnetic properties, microstructure and anti-corrosion properties of Dy-surface-alloying NdFeB magnets obtained via magnetron sputtering and thermal diffusion were evaluated. The Hcj of the Dy95Al5–NdFeB magnet increases by 32.68%, while the remanence declines slightly. Furthermore, X-ray diffraction and microstructural analysis confirm the formation of Dy-rich shells, the higher-magnetic-anisotropy field of hard (NdxDy1−x)2(FeAl)14B magnetic phases and an optimised grain boundary structure, contributing to the Hcj enhancement of the magnet. The elemental distribution and diffusion mechanism of the magnets are also discussed. Moreover, the corrosion resistance of the Dy95Al5–NdFeB magnet is substantially improved by enhancing the electrochemical stability and optimising the distribution and morphology of the intergranular phases. The findings of this study are of substantial importance in the development of low-heavy rare-earth sintered NdFeB magnets.

Structurally dependent electroconductivity properties of ultrafine composites α-FeOOH/α-Fe2O3

In articles first time to presents approach to obtaining of ultrafine defective composite α-FeOOH/α-Fe2O3 by hydrothermal synthesis and investigated the influence of post-processing on phase transformations, magnetic microstructure and elecroconductivity. The X-ray analysis, Mossbauer spectroscopy, IR spectroscopy and impedance spectroscopy used to analyzed the structural-morphological and elecroconductivity. It was established that the selection of the parameters of the synthesis to possible the control of the processes of nucleation, aggregation and restructuring of the formed defective composite. Theories of thermo-induced reorganization of different phase structures and the formation of the intrinsic semiconductorness as a result of internal activation are updated.

The Effect of Annealing on the Soft Magnetic Properties and Microstructure of Fe82Si2B13P1C3 Amorphous Iron Cores.

This research paper investigated the impact of normal annealing (NA) and magnetic field annealing (FA) on the soft magnetic properties and microstructure of Fe82Si2B13P1C3 amorphous alloy iron cores. The annealing process involved various methods of magnetic field application: transverse magnetic field annealing (TFA), longitudinal magnetic field annealing (LFA), transverse magnetic field annealing followed by longitudinal magnetic field annealing (TLFA) and longitudinal magnetic field annealing followed by transverse magnetic field annealing (LTFA). The annealed samples were subjected to testing and analysis using techniques such as differential scanning calorimetry (DSC), transmission electron microscopy (TEM), X-ray diffraction (XRD), magnetic performance testing equipment and magneto-optical Kerr microscopy. The obtained results were then compared with those of commercially produced Fe80Si9B11. Fe82Si2B13P1C3 demonstrated the lowest loss of P1.4T,2kHz = 8.1 W/kg when annealed in a transverse magnetic field at 370 °C, which was 17% lower than that of Fe80Si9B11. When influenced by the longitudinal magnetic field, the magnetization curve tended to become more rectangular, and the coercivity (B3500A/m) of Fe82Si2B13P1C3 reached 1.6 T, which was 0.05 T higher than that of Fe80Si9B11. During the 370 °C annealing process of the Fe82Si2B13P1C3 amorphous iron core, the internal stress in the strip gradually dissipated, and impurity domains such as fingerprint domains disappeared and aligned with the length direction of the strip. Consequently, wide strip domains with low resistance and easy magnetization were formed, thereby reducing the overall loss of the amorphous iron core.

Facile preparation of bonded NdFeB/SmFeN hybrid magnets with flexibility, anisotropy and high energy density

The application of rubber isotropic bonded magnets is limited due to low energy density, although it remainsunbeatableintermsofprice and production rate. In this paper, high-filled, flexible, and anisotropic NdFeB/SmFeN bonded magnets were prepared using mixtures of fine SmFeN powders and coarse NdFeB powders by calendering molding. The optical microscope images show that adding fine SmFeN powder benefits processability, leading to higher loading while retaining flexibility. The magnetic property and microstructure of the magnets display the anisotropic magnetic property of NdFeB/SmFeN bonded magnets derived from the arrangement of the platelet-shaped NdFeB particles induced by mechanical stress during the calendaring process. To further optimize the magnetic properties of NdFeB/SmFeN bonded magnets, the NdFeB was sieved and then mixed with SmFeN to mold into sheets. Finally, the effect of NdFeB particle size on the magnetic and mechanical properties of NdFeB/SmFeN bonded magnets was investigated. The results showed that when the particle size of the NdFeB particle was 75–100 µm, the magnetic properties of magnets reached the maximum value (Br = 7.77 KG, Hcj = 14.70 KOe, (BH)max = 12.70 MGOe) with density of 5.59 g/cm3. In addition, the tensile strength of the NdFeB/SmFeN bonded magnets increases and the sample standard deviation narrows with decreasing NdFeB particle size. This method provides a facile preparation for anisotropic bonded magnets with a new energy density record of rubber bonded rolled magnets prepared without an external field.

Magnetic Bead Spherical Nucleic Acid Microstructure for Reliable DNA Preservation and Repeated DNA Reading.

DNA is an attractive medium for long-term data storage because of its density, ease of copying, sustainability, and longevity. Recent advances have focused on the development of new encoding algorithms, automation, and sequencing technologies. Despite progress in these subareas, the most challenging hurdle in the deployment of DNA storage remains the reliability of preservation and the repeatability of reading. Herein, we report the construction of a magnetic bead spherical nucleic acid (MB-SNA) composite microstructure and its use as a cost-effective platform for reliable DNA preservation and repeated reading. MB-SNA has an inner core of silica@γ-Fe2O3@silica microbeads and an outer spherical shell of double-stranded DNA (dsDNA) with a density as high as 34 pmol/cm2. For MB-SNA, each strand of dsDNA stored a piece of data, and the high-density packing of dsDNA achieved high-capacity storage. MB-SNA was advantageous in terms of reliable preservation over free DNA. By accelerated aging tests, the data of MB-SNA is demonstrated to be readable after 0.23 million years of preservation at -18 °C and 50% relative humidity. Moreover, MB-SNA facilitated repeated reading by facile PCR-magnetic separation. After 10 cycles of PCR access, the retention rate of dsDNA for MB-SNA is demonstrated to be as high as 93%, and the accuracy of sequencing is more than 98%. In addition, MB-SNA makes cost-effective DNA storage feasible. By serial dilution, the physical limit for MB-SNA to achieve accurate reading is probed to be as low as two microstructures.

Pr–Tb synergistic strengthening on coercivity of Nd-Ce-Fe-B magnets grain boundary diffused with Pr-Tb-Al-Ga alloys

Sintered Nd-Ce-Fe-B magnets were grain boundary diffused (GBDed) with PrxTb80–xAl10Ga10 (at%) (x = 0, 20, 40, 60, 80) alloys. The effect of Pr/Tb content in diffusion source on magnetic properties, microstructure and elements distribution of GBDed magnets was investigated. When Pr is used to substitute for 75% Tb in diffusion source, Tb consumption per unit coercivity improvement of GBDed magnet reduces by 77%, compared with the Tb80Al10Ga10 diffused magnet. Tb element diffuses into magnets and then forms Tb-rich shell with high magneto-crystalline anisotropy field surrounding main phase grains, resulting in substantial coercivity improvement. Pr with low melting point diffuses deeply along liquid grain boundary phase during GBD process. It can eliminate some sharp defects of main phase grains and make grain boundaries smooth, which provides diffusion channels for further diffusion of Tb element. Therefore, there are more diffusion channels for Tb and less Tb enriched at surface region, making Tb diffuse more deeply and improving Tb utilization efficiency. This method significantly improves the coercivity, and realizes the green, efficient and high-quality utilization of heavy rare earth (HRE) elements.

Temporal electron-spin splitter based on a novel semiconductor magnetic quantum microstructure with zero average magnetic fields

The dwell time is calculated for electron in a novel magnetic nanostructure with zero average magnetic fields, which is realized experimentally by constructing three nanosized ferromagnetic stripes on top and bottom of the InAs/AlxIn1-xAs heterostructure. Although structural magnetic fields are averagely equal to naught, the dwell time is still dependent on electron spins owing to the spin-field interaction. Due to the dependence of effective potential experienced by electron on structural parameters (such as magnetic strength and device width), spin-polarized dwell time can be conveniently modulated by reasonably fabricating ferromagnetic stripes. As a result, this novel magnetic microstructure can act as a temporal electron-spin splitter for spintronic device applications.

Effect of Ag microalloying on the magnetic properties and microstructure of Fe–P–C amorphous alloys

In this work, a series of Fe80−xAgxP13C7 (x = 0, 0.4, 0.6, and 1.0 at. %) amorphous/nanocrystalline alloys with high saturation magnetization (Ms) and excellent bending ductility were produced through melt spinning. The effect of Ag microalloying on the thermostability, microstructure, and soft magnetic properties was then investigated in detail. We observed that the doping of Ag could increase the value of Ms, without significantly deteriorating the coercive force. The increase in Ms was due to the precipitation of α-Fe nanocrystals, caused by Ag, which had a positive mixing enthalpy and immiscibility with iron, resulting in phase decomposition and acting as sites for α-Fe nanocrystalline nucleation. This work offers a promising method for preparing soft magnetic materials with amorphous/nanocrystalline structures and good bending ductility, without annealing.

The δ-doping manipulable temporal spin splitter for electron in semiconductor magnetic quantum microstructure

We theoretically investigate the effect of a δ-potential to a temporal spin splitter for electron in a semiconductor magnetic quantum microstructure (SMQM), which is realized by patterning a perpendicularly-magnetized ferromagnetic stripe on top of InAs/AlxIn1-xAs. The dwell time for electron in the δ-doped SMQM is still spin polarized, because electron spin interacts with structural magnetic field. The spin-dependent dwell time is modulated by switching the δ-potential owing to the dependence of effective potential felt by electron on the δ-doping. These significant findings demonstrate that such a δ-doped SMQM acts as a manipulable temporal electron-spin splitter, which may be helpful for design of spintronic devices.

Hygroscopic properties of whey protein hydrolysates and their effects on water retention in pork patties during repeated freeze–thaw cycles

The hygroscopic properties, water migration properties and micromorphology of native whey protein (NWP) and whey protein hydrolysate (WPH) under different relative humidity (RH) conditions were assessed in this study. Moreover, their effects on water retention in pork patties during freeze–thaw (F–T) cycles were assessed. The results showed that the moisture absorption rate of WPH was 7.45 percentage units higher than that of NWP after the moisture content balance. When the RH reached 97.0%, the equilibrium moisture content of WPH was 1.81 times that of NWP. Combined with low-field nuclear magnetic resonance and microstructure results, WPH exhibited the strongest moisture absorption and moisturising abilities and was more suitable for addition to meat systems. Furthermore, the addition of WPH effectively improved water retention in pork patties during F–T cycles. After seven F–T cycles, the addition of 15% WPH effectively inhibited myofibrillar protein degradation and microstructural damage, reduced the relative content of α-helix and the water holding capacity loss of pork patties and enhanced proton density. These results indicate that WPH has the potential to be used as a water retention agent candidate to reduce the quality loss of meat products during F–T cycles.

Ultrahigh coercivity and excellent thermal stability of hot-deformed Nd-Fe-B magnets by the diffusion of (Pr,Nd)-Dy-Cu-Al

The effects of the addition of (Pr0.25Nd0.75)10Dy80Cu5Al5 alloy powders on the magnetic properties and microstructure of the hot-deformed Nd-Fe-B magnets were investigated in this work. Through the addition of (Pr0.25Nd0.75)10Dy80Cu5Al5, an ultrahigh coercivity of 3.14 T was obtained in a 6-mm-thick hot-deformed magnet, and the temperature coefficient of coercivity and remanence were improved from −0.475%/℃ and −0.145%/℃ to −0.383%/℃ and −0.110%/℃ at 20 −180 ℃, respectively, showing the excellent thermal stability. Microstructure observations indicated that the formation of thick nonferromagnetic intergranular phase, the reduction of grain size and aspect ratio and the formation of the (Nd,Pr,Dy)2Fe14B main phase were achieved after the addition of (Pr0.25Nd0.75)10Dy80Cu5Al5, which were the main reasons for the enhancement of coercivity and thermal stability.

Magnetic Properties and Microstructures of Spark Plasma Sintered Sm-Co-Fe-Cu-Zr-Hf Magnets Under Various Heat Treatment Conditions

Magnetic Properties and Microstructures of Spark Plasma Sintered Sm-Co-Fe-Cu-Zr-Hf Magnets Under Various Heat Treatment Conditions

Magnetic properties, crystalline and magnetic microstructures of dual-main-phase (Nd, Ce)-Fe-B sintered magnets

The (Nd, Ce)-Fe-B sintered magnets were prepared by a dual-main-phase (DMP) process under the same conditions using different combinations of Nd-Fe-B with Ce-Fe-B and (Nd, Ce)-Fe-B strips. The crystalline and magnetic microstructures of DMP (Nd, Ce)-Fe-B magnets with the remanence of 11.92–12.68 kGs, the intrinsic coercivity of 3.97–5.31 kOe, and the maximum energy product of 23.08–32.99 MGOe have been investigated. Magnetic force microscope (MFM) investigations reveal that the DMP (Nd, Ce)-Fe-B magnets show maze-like patterns, which are like that of standard anisotropy Nd-Fe-B sintered magnets by and large. However, much finer domain structures mixing with coarse ones can be observed obviously in DMP (Nd, Ce)-Fe-B sintered magnets. The size distribution of the domain width of the DMP (Nd, Ce)-Fe-B magnet is not uniform obviously. The average domain width is W = 0.912 μm, and the fine domain width has only 0.216 μm. The smaller domain width and more branch domain patterns exist in poorer coercivity DMP magnets. This is caused by the non-uniform Ce composition of poorer property DMP magnets and the grain boundary microstructure that is not conducive to improving the coercivity. Furthermore, it is found that some domains of rare-earth-rich grain boundary phases exhibit the characteristics of plate-like patterns rather than no-contrast by using MFM, indicating their ferromagnetism. Obvious correlations between the crystalline microstructure, chemical composition of phases, and magnetic structure were demonstrated for the DMP magnets.

Effect of annealing on the magnetic microstructure of high-pressure torsion iron: the relevance of higher-order contributions to the magnetic small-angle neutron scattering cross section.

The development of higher-order micromagnetic small-angle neutron scattering theory in nanocrystalline materials is still in its infancy. One key challenge remaining in this field is understanding the role played by the microstructure on the magnitude and sign of the higher-order scattering contribution recently observed in nanocrystalline materials prepared by high-pressure torsion. By combining structural and magnetic characterization techniques, namely X-ray diffraction, electron backscattered diffraction and magnetometry with magnetic small-angle neutron scattering, this work discusses the relevance of higher-order terms in the magnetic small-angle neutron scattering cross section of pure iron prepared by high-pressure torsion associated with a post-annealing process. The structural analysis confirms: (i) the preparation of ultra-fine-grained pure iron with a crystallite size below 100 nm and (ii) rapid grain growth with increasing annealing temperature. The analysis of neutron data based on the micromagnetic small-angle neutron scattering theory extended to textured ferromagnets yields uniaxial magnetic anisotropy values that are larger than the magnetocrystalline value reported for bulk iron, supporting the existence of induced magnetoelastic anisotropy in the mechanically deformed samples. Furthermore, the neutron data analysis revealed unambiguously the presence of non-negligible higher-order scattering contributions in high-pressure torsion iron. Though the sign of the higher-order contribution might be related to the amplitude of the anisotropy inhomogeneities, its magnitude appears to be clearly correlated to the changes in the microstructure (density and/or shape of the defects) induced by combining high-pressure torsion and a post-annealing treatment.

Unraveling the relationship between a tonalitic pluton and shear zones: Insights from magnetic fabrics and microstructures of the Alto Maranhão batholith, Mineiro belt, southern São Francisco craton

The Alto Maranhão batholith (SE Brazil) comprises granitic juvenile arc-related rocks within the Paleoproterozoic Mineiro Belt. The pluton is bounded by the NE-SW sinistral Jeceaba-Bom Sucesso (JBSZ) and NW-SE dextral Congonhas-Itaverava (CISZ) shear zones. Field, microstructural and magnetic fabric studies were employed in order to constrain its emplacement model and the spatial and temporal relationships between plutons and shear zones during Paleoproterozoic orogenic events. Combined meso- and microscale fabric analyses allowed us to individualize two different domains or lobes across the intrusion. The magmatic foliation, defined by biotite and hornblende, strikes NE-SW in the western lobe and rotates to NW-SE in the eastern lobe, moderately to steeply dipping, trending accordingly with the solid-state foliation exhibited by the country rocks. Field observations show that magmatic structures are preserved, such as elongated to rounded syn-magmatic enclaves and magmatic layering. The microstructures described for both domains are a direct record that deformation occurs locally and under magmatic conditions, with limited features of solid-state deformation such as undulose extinction in quartz and plagioclase on both tonalite and dioritic enclaves. AMS data exhibits dominantly steep magnetic lineations in the eastern lobe of the intrusion, except for sampling sites close to the CISZ, whose lineations are shallowly plunging. In both cases, the magnetic lineation trends NW-SE. Towards the western lobe, the magnetic lineation becomes horizontal and randomly oriented close to its westernmost tip. The magnetic and magmatic foliations follow the same orientation, therefore striking NW-SE in the eastern lobe and NE-SW in the west. Considering the batholith's heterogeneities highlighted by the AMS measurements, we suggest that the eastern lobe of the intrusion is characterized as a feeder zone in which magma was injected along the CISZ, being subsequently spread into the pluton's western lobe, until being stopped by a rheological barrier defined by JBSZ and country rocks, controlling its boomerang-like form. The proposed emplacement model suggests that the Alto Maranhão batholith was emplaced in a contractional site, by arc-normal dextral simple shear revealing that transcurrent deformation was taking place concurrently with the growth of the São Francisco paleocontinent, and addition of mantle-derived magmas to the continental crust.