Magnetic Coercivity Research Articles

Uniaxial Magnetization and Electrocatalytic Performance for Hydrogen Evolution on Electrodeposited Ni Nanowire Array Electrodes with Ultra-High Aspect Ratio.

Ni nanowire array electrodes with an extremely large surface area were made through an electrochemical reduction process utilizing an anodized alumina template with a pore length of 320 µm, pore diameter of 100 nm, and pore aspect ratio of 3200. The electrodeposited Ni nanowire arrays were preferentially oriented in the (111) plane regardless of the deposition potential and exhibited uniaxial magnetic anisotropy with easy magnetization in the axial direction. With respect to the magnetic properties, the squareness and coercivity of the electrodeposited Ni nanowire arrays improved up to 0.8 and 550 Oe, respectively. It was also confirmed that the magnetization reversal was suppressed by increasing the aspect ratio and the hard magnetic performance was improved. The electrocatalytic performance for hydrogen evolution on the electrodeposited Ni nanowire arrays was also investigated and the hydrogen overvoltage was reduced down to ~0.1 V, which was almost 0.2 V lower than that on the electrodeposited Ni films. Additionally, the current density for hydrogen evolution at -1.0 V and -1.5 V vs. Ag/AgCl increased up to approximately -580 A/m2 and -891 A/m2, respectively, due to the extremely large surface area of the electrodeposited Ni nanowire arrays.

Investigation on PECVD-deposited SiO2 underlayer in permalloy-based magnetoelectronic devices

This study presents a comprehensive investigation into the dependence among processing conditions, surface properties of the PECVD-deposited SiO2 underlayer, and their consequential impact on the magnetic and film properties of permalloy. The key exploration parameters involve variations in deposition temperature and annealing temperature. By varying the parameters, microstructure changes within SiO2 were firstly analyzed. A thorough characterization of in-plane magnetic features of the Ni81Fe19/SiO2 multilayer film was then undertaken. The results reveal a significant reliance of magnetic anisotropy and coercivity on PECVD SiO2 deposition temperatures, particularly evident for deposition temperatures below 350°C. This effect is attributed to the formation of a suboxide SiOx film at a lower deposition temperature, which typically possesses more dangling bond and lattice defects, resulting in the formation of surface granular structures after annealing. These characterizations may lead to the identification of optimized processing conditions, which may be used for enhancing the performance of anisotropic magnetoresistance devices with SiO2 as an underlayer. Furthermore, the research findings extend beyond anisotropic magnetoresistance systems, with implications for a broad utilization of magnetoelectronic devices. Overall, the study provides a foundation for informed decision-making in the design and optimization of magnetoelectronic devices, in particular for integrated circuit incorporated devices, highlighting the potential for enhanced functionality through manipulation of processing conditions.

Effect of Sn4+–Co2+ co-substitution on structural and magnetic properties of SrFe12-2xSnxCoxO19 M–type strontium ferrite

With the continuous improvement of the performance of M–type ferrite, it has been paid more attention to and become more and more popular, and it has been applied to social production and development. For improving the magnetic properties of ferrite, the most common method used by researchers is ion replacement. This method of improving magnetic properties is the mainstream of research. In this study, SrFe12-2xSnxCoxO19 (x = 0, 0.05, 0.1, 0.15, 0.2) strontium ferrite with Sn4+ and Co2+ co-substitution was prepared using ceramic technology. The influence of Sn4+ and Co2+ co-substitution on the structure and magnetism of strontium ferrite were analyzed. X-ray diffraction analysis shows that as the substitution amount of Sn4+ and Co2+ ions increased, the main structure of strontium ferrite remained hexagonal. The morphology of the samples was analyzed by scanning electron microscope, and the results showed that the morphology of ferrite was mainly hexagonal strontium ferrite. Magnetic property show that the remanence (Br), coercivity (Hcj) and saturation magnetization (Ms) of the sample first increased and then decreased with the Sn4+- Co2+ ions increase of doping amount. When the substitution amount x = 0.15, the Ms reaches its maximum value of 83.8 emu/g, the Br reaches its maximum value of 405.4 mT. And when the substitution amount x = 0.05, Hcj reaches its maximum value of 312.5 kA·m−1.

Enhancement of the magnetic property of Nd-Fe-B sintered magnets through novel powder rounding modification

Two types of sintered Nd-Fe-B magnets were fabricated by the process of powder metallurgy technology through two different powder preparation processes i.e., conventional powder preparation process and novel powder rounding modification. The microstructure, composition and properties of the two type powders have been studied including the particle size distributions and flowabilities. Furthermore, magnetic properties, microstructure and alignment degree of the magnets prepared by the corresponding powder also have been investigated. The novel powder rounding modification rounds the sharp edges and corners of the particles compared to the conventional powder preparation process, thereby reducing friction between the particles and improving flowability of the powder. As a result, the alignment degree of the sintered magnet is enhanced, which contribute to the improvement of the remanence and the energy product density. The powder that experienced rounding process changed the distribution of RE (rare earth)-rich particles, causing tiny RE-rich particles to adhere around the main phase particles, facilitating the compact of bulk during liquid-phase sintering process and achieving uniform distribution of RE-rich phases around the Nd2Fe14B main phase, resulting in increasing the magnet density and coercivity. As a consequence, we have produced the magnet with Br = 1.43 T, Hcj = 1049 kA/m and (BH)max = 393.2 kJ/m3, which is fully superior to conventional magnet with Br = 1.41 T, Hcj = 969 kA/m and (BH)max = 383.7 kJ/m3 by adopting powder rounding process. This indicates that the novel powder rounding modification is an efficient approach for synchronous improvement of magnetic performance of sintered Nd-Fe-B without any heavy rare earth elements.

Effect of Nb doping on the magnetic properties and its fluxgate behavior of CoFeNbSiB amorphous ribbons

Co-based amorphous alloys are often utilized as magnetic core for fluxgate sensor due to their excellent comprehensive performance with eminent permeability and insignificant coercivity. Herein, we investigated the effects of Nb doping on the phase composition, amorphous formation, magnetic domain structure and soft-magnetic characteristics of (Co0.7Fe0.5Si0.15B0.1)100-xNbx (x = 0, 1, 3, 5, 7) alloy ribbons and its fluxgate performance. Additionally, related magnetic parameters as magnetic permeability μi and coercivity Hc of the ribbon under zero magnetic-field annealing (ZFA) as well as longitudinal magnetic-field annealing (LFA) and fluxgate sensitivity and noise value were also tested. It is verified that the Nb doping is well able to optimize their amorphization, thermostability and soft magnetic properties. When x = 3, the ribbon presents the most well-distributed magnetic domain structure and the inferior soft magnetic properties, with an initial permeability μi of 8900 and a coercivity Hc of 1.51 A/m. Compared with ZFA, LFA is more effective on improving the soft magnetic and fluxgate behavior. The highest μi of 24,520 and the lowest Hc of 0.18 A/m are obtained at x = 3 for the LFA sample, where the fluxgate sensitivity is up to 44.15 mV/μT, accompanied by the peak-to-peak noise (denoted by Noisep-p) value is as low as 1.38 nT.

Comparison of the Magnetic and Structural Properties of MnFePSi Microwires and MnFePSi Bulk Alloy.

We provide comparative studies of the structural, morphological, microstructural, and magnetic properties of MnFePSi-glass-coated microwires (MnFePSi-GCMWs) and bulk MnFePSi at different temperatures and magnetic fields. The structure of MnFePSi GCMWs prepared by the Taylor-Ulitovsky method consists of the main Fe2P phase and secondary impurities phases of Mn5Si3 and Fe3Si, as confirmed by XRD analysis. Additionally, a notable reduction in the average grain size from 24 µm for the bulk sample to 36 nm for the glass-coated microwire sample is observed. The analysis of magnetic properties of MnFePSi-glass-coated microwires shows different magnetic behavior as compared to the bulk MnFePSi. High coercivity (450 Oe) and remanence (0.32) are observed for MnFePSi-GCMWs compared to low coercivity and remanent magnetization observed for bulk MnFePSi alloy. In addition, large irreversibility at low temperatures is observed in the thermal dependence of magnetization of microwires. Meanwhile, the bulk sample shows regular ferromagnetic behavior, where the field cooling and field heating magnetic curves show a monotonic increase by decreasing the temperature. The notable separation between field cooling and field heating curves of MnFePSi-GCMWs is seen for the applied field at 1 kOe. Also, the M/M5K vs. T for MNFePSi-GCMWs shows a notable sensitivity at a low magnetic field compared to a very noisy magnetic signal for bulk alloy. The common features for both MnFePSi samples are high Curie temperatures above 400 K. From the experimental results, we can deduce the substantial effect of drawing and quenching involved in the preparation of glass-coated MnFePSi microwires in modification of the microstructure and magnetic properties as compared to the same bulk alloy. The provided studies prove the suitability of the Taylor-Ulitovsky method for the preparation of MnFePSi-glass-coated microwires.

Macroscopic demagnetization of the sintered Nd-Fe-B magnets prepared by Tb grain boundary diffusion

Macroscopic demagnetization in sintered Nd-Fe-B magnets by Tb grain boundary diffusion (GBD) is investigated in comparison with non-GBD ones. Demagnetization curves, the coercivity distributions, Tb content, and magnetic fields of the magnets at various external fields (μ0Hext) are analyzed. As μ0Hext approaches coercivity of the GBD magnet, S-N poles form near the center, between and parallel to the original N-S poles, indicating the magnetization reversal near the center of the GBD magnet. This is distinguished from the non-GBD magnets where demagnetization occurs mainly in the pole surfaces. The mechanism for macroscopic demagnetization is discussed.

Nanocrystalline Fe(Co)ZrMoBCu soft magnetic alloys: A transmission electron microscopy study of the microstructures

Nanocrystalline Fe81Zr7Mo2B9Cu1 and Fe40.5Co40.5Zr7Mo2B9Cu1 alloy ribbons were prepared by annealing the as-quenched amorphous alloys at their first exothermic peak temperature. The primary crystallization phases of Fe81Zr7Mo2B9Cu1 and Fe40.5Co40.5Zr7Mo2B9Cu1 consisted of nanoscale body-centered cubic α-Fe and α-FeCo grains, respectively. The microstructures and compositions were analyzed via transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM), and area maps were obtained through energy-dispersive spectroscopy (EDS). The addition of Co decreased the mean grain size (D) and broadened the grain-size distribution (σ). The effect of the addition of Co on the Cu clusters and element distribution was studied in detail. Scanning transmission electron spectroscopy combined with energy-dispersive spectroscopy revealed that both alloys contained Cu clusters; the Fe40.5Co40.5Zr7Mo2B9Cu1 alloy exhibited a Cu-cluster density similar to that of the Fe81Zr7Mo2B9Cu1 alloy. Both alloys contained relatively less Fe in their residual amorphous phases than in their nanocrystals, with the nanocrystals in Fe40.5Co40.5Zr7Mo2B9Cu1 containing less Co than in the residual amorphous phase. Fe40.5Co40.5Zr7Mo2B9Cu1 exhibited higher specific saturation magnetization (Ms), specific remanent magnetization (Mr) and larger coercivity (Hc) than Fe81Zr7Mo2B9Cu1.

Robustness of magnetocrystalline anisotropy and coercivity in Fe–Co–B

As a potential candidate for critical chemical element free permanent magnet, (Fe0.7Co0.3)2B, shows promising intrinsic magnetic properties, including large magnetization, high Curie temperature and moderate magnetocrystalline anisotropy (MCA). Still, the coercivity that has been achieved is relatively low. To understand and improve coercivity, we study the robustness of MCA related to the fluctuation of chemical composition and the structural distortion and its effect on coercivity in (Fe0.7Co0.3)2B from first principles DFT (density functional theory) calculation and micromagnetic simulation. A fluctuation of cobalt content of 10%, or 1% isotropic lattice strain, or 2% tetragonal distortion reduces MCA energy up to 30%. By considering randomly distributed local MCA energy reduction up to 30%, the calculated coercivity of anisotropic bulk magnets reduced from 3.6 kOe to 2.2 kOe. Rational microstructure design, such as grain size refinement and development of strong crystal texture of MCA easy-axis (i.e., degree of alignment for (Fe0.7Co0.3)2B grains), can enhance coercivity and mitigate the effect of local MCA reduction. In addition to acceptable intrinsic magnetic properties, the promising hard magnetic phase needs good MCA robustness to facilitate the development of practical magnets.

Tailoring magnetic softness of Fe-based amorphous alloys with superior magnetization by magnetic field annealing

The inverse relationship between the saturation magnetic flux density (Bs) and coercivity (Hc) of Fe-based amorphous alloys is a very active research topic that has been extensively debated. In this work, we conducted a detailed investigation on the magnetic softness of Fe83.2-xCoxB10C6Cu0.8 (x = 0 and 6 at.%) amorphous alloys based on analysis of the surface morphology, microstructure, magnetic anisotropy, and magnetic domain structure. Enhanced magnetic softness-magnetization synergy was realized in the present alloys by magnetic field annealing (MFA) during the de-stressing process. A dramatic 84 % reduction of Hc to 2.2 A/m was achieved for the Co-doped alloy under MFA, exhibiting excellent magnetic performance with a superb Bs of 1.86 T. The consistency between the experimental results and theoretical analysis revealed that the MFA process can mitigate the trade-off between stress-induced anisotropy and induced uniaxial anisotropy owing to the homogenized structure formed by field annealing. Thus, the process favored a low Hc due to the significant continuous decline in the total magnetic anisotropy, which coincided well with the results of Magneto-optical Kerr microscopy. The study elucidates a mechanism for tuning Hc in Co-doped alloy systems and affords a possible pathway for softening amorphous alloys with high Bs.

Machine learning based prediction of mechanical properties of WC-Co cemented carbides from magnetic data only

Based on experimental data and extensive experience, magnetic coercivity and saturation moment are traditionally used to estimate the microstructure and quality of cemented carbides, especially in the manufacturing industry. This work demonstrates that predictions of the structural and mechanical properties of manufactured WC-Co elements can be derived in principle from magnetic data alone using an artificial neural network (ANN). A collection of WC-Co pellet samples with a wide variety of powder compositions and processing parameters was produced to cover a wide range of characteristic features for ANN training. The total field distribution, extracted from first-order-reversal-curves, serves as input data for the ANN. Microstructural parameters such as mean grain size and mechanical properties such as hardness and fracture toughness can be derived from the purely magnetic measurements with high accuracy, while the transverse rupture strength shows large errors and cannot be predicted.

Study on Microwave Absorption Performance of Submicron SrFe12O19 Particles Prepared by Hydrothermal Method

: Strontium hexaferrite (SrFe12O19) materials were synthesized through the hydrothermal method with conditions at R= (Fe3++ Sr2+)/(OH ̶) ratio of 2 to 4 (R ratio of 1/2, 1/3 and 1/4 were, respectively abbreviated to M2, M3 and M4). R has been examined by employing Fe(NO3)3 and Sr(NO3)2 as the initial materials. The effects of R ratio on the structure, particle size, magnetic and microwave-absorbing properties of the samples were studied. The coercivity and saturation magnetization of M4 sample reach 5.2 kOe and 58.7 emu/g, respectively. The optimal reflection loss of the M4 at the thickness of 1.5 mm reached a value as large as - 48.27 dB in the frequency range of 2 to 18 GHz. The improvement in microwave absorption performance of M4 sample compared to M2 and M3 was mainly resulted from the increased magnetic properties with increasing R ratio. 
 

Strain‐Modulated Ferromagnetism at an Intrinsic van der Waals Heterojunction

AbstractThe van der Waals interaction enables atomically thin layers of exfoliated 2D materials to be interfaced in heterostructures with relaxed epitaxy conditions, however, the ability to exfoliate and freely stack layers without any strain or structural modification is by no means ubiquitous. In this work, the piezoelectricity of the exfoliated van der Waals piezoelectric α‐In2Se3 is utilized to modify the magnetic properties of exfoliated Fe3GeTe2, a van der Waals ferromagnet, resulting in increased domain wall density, reductions in the transition temperature ranging from 5 to 20 K, and an increase in the magnetic coercivity. Structural modifications at the atomic level are corroborated by a comparison to a graphite/α‐In2Se3 heterostructure, for which a decrease in the Tuinstra‐Koenig ratio is found. Magnetostrictive ferromagnetic domains are also observed, which may contribute to the enhanced magnetic coercivity. Density functional theory calculations and atomistic spin dynamic simulations show that the Fe3GeTe2 layer is compressively strained by 0.4%, reducing the exchange stiffness and magnetic anisotropy. The incorporation of α‐In2Se3 may be a general strategy to electrostatically strain interfaces within the paradigm of hexagonal boron nitride‐encapsulated heterostructures, for which the atomic flatness is both an intrinsic property and paramount requirement for 2D van der Waals heterojunctions.

Influence of doping concentrations on the structural, optical, and magnetic properties of Ba-doped LaCoO3 nanostructure

Abstract In this article we report the structural, morphology, vibrational, optical and magnetic properties of Ba x La1−x CoO3 (x = 0, 0.05, and 0.1) (LBCO) samples. The X-ray diffraction shows that samples are in single rhombohedral phase. The Raman signals of LCO were quite small in comparison to LBCO, which exhibited a Raman peak above 675 cm−1. The band seen with a wavenumber of 484 cm−1 corresponds to the vibrational modes of E g bending and Ba–O stretching. UV–DRS and photoluminescence spectra indicated broad absorption over the ultraviolet, visible, and near-infrared spectrums. Surface morphology and EDAX spectra corroborated the materials homogeneous size distribution and homogenous microstructure, with Ba indicating a more stable structure. XPS was used to study chemical states of LBCO and found Co (2p), La (3d), O (1s), and C (1s) elements in perovskite compounds. A peak beneath 300 eV indicated adventitious carbon on surface materials. XPS survey spectrum elements La, Ba, Co, and O had their own binding energies. The magnetization-field dependency of LBCO at 300 K showed that Ba insertion into the LCO switched it from paramagnetic to weak ferromagnetic. Ba considerably decreased magnetic saturation and coercivity, influencing magneto-crystallites’ anisotropy and coercive field.

Understanding the coercivity enhancement mechanism of grain boundary diffused Nd-Fe-B magnets by comparing with commercial equivalent coercivity magnets

The grain boundary diffusion (GBD) technology effectively utilizes heavy rare earth (HRE) elements to improve the coercivity of sintered Nd-Fe-B magnet. Significantly, clarifying its coercivity improvement mechanism is essential for further optimizing the process and performance. Through comparative analysis with commercial conventional magnets (CSH) processing equivalent coercivity, this study investigated the specific mechanism by which the GBD method enhances the coercivity of HRE elements in an efficient manner. To achieve the same coercivity (∼21.4 kOe), GBD magnets contained only 0.25 wt% Tb, whereas CSH magnets had 1.17 wt% Dy and 1.18 wt% Tb. The microstructure analysis revealed that the Tb element in the GBD magnet was concentrated in the outer layer of the grain, constituting 17.37 wt% of the total rare earth content. While, in CSH magnets, the HRE element in the main phase grains accounted for only 9.58 wt% of the total rare earth elements, including Dy (3.83 wt%) and Tb (5.75 wt%). The characteristic core-shell structural grains in GBD magnet also endowed it with an uneven magnetic domain structure and a more concentrated “abrupt” magnetization reversal. Based on the characterization results the nucleation positions of the two types of magnets were analyzed by fitting Hci/Ms and Ha/Ms. The results can serve as a guide for enhancing coercivity in grain boundary diffusion sintered Nd-Fe-B magnets, aiding in process and property optimization, and advancing the understanding of nucleation type mechanisms.

Physical characterization, magnetic interactions and DC electrical resistivity properties of La3+ substituted NiZnCd nano ferrites

In this article, we substituted La3+ ions to explore the structural, magnetic, and DC electrical resistivity properties of Ni0.5Zn0.4Cd0.1Fe2-xLaxO4 (x = 0.0, 0.02, 0.04, 0.06, and 0.08) nano-structured spinel ferrites. We employed X-ray diffraction (XRD), Field-emission scanning electron microscopy (FESEM) with Energy dispersive X-ray (EDX), Fourier transform infrared spectroscopy (FTIR), Vibrating sample magnetometry (VSM), and electrical measurements to characterize the studied samples, which were synthesized using the sol–gel auto-combustion process. XRD analysis confirmed that the prepared materials formed a single-phase nanostructure. Using Debye-Scherer's formula, we calculated the average crystallite size, which ranged from 29.01 to 21.52 nm. FESEM images demonstrated that each sample exhibited spherical nanocrystalline behavior. The variations of the prepared samples were confirmed constitutionally by EDX. The FTIR data revealed two absorption bands for all synthesized materials at υ1 = 562.18 to 590.51 cm−1 and υ2 = 410.18 to 430.51 cm−1, corresponding to the tetrahedral and octahedral sites of the spinel structure, respectively. Vibrant sample magnetometry spectra were utilized to investigate how La3+-doping affects the magnetic characteristics of NiZnCd ferrite. Due to enhanced La3+-doping, saturation magnetization, and coercivity values decreased. The La3+ doping of NiZnCd nano ferrites resulted in changes in saturation magnetization (from 83.66 to 69.57 emu/g), coercivity (from 33.75 to 60.51 Oe), and remanence magnetization (from 29.62 to 33.12 emu/g). These variations suggest the potential utility of the samples for magnetic recording and memory applications. The semiconducting behavior has been confirmed by the DC electrical resistivity measured values using a two-probe method. Data on DC electrical resistivity were also utilized to determine carrier concentration and activation energy, establishing a connection with La3+ replacement.

Synthesis, characterization, and modeling of gelatin-based magnetic hydrogel beams

Hydrogels are soft materials that can be designed to be responsive to external stimuli such as temperature, pH change, and electric and magnetic fields. Magnetically responsive hydrogels consisting of polymer, water, and magnetic nanoparticles (MNPs) are emerging candidates in biomedical fields due to their remote application. In this work, cobalt ferrite-based MNPs prepared by the auto-combustion method are embedded in gelatin hydrogels. Cobalt ferrite-based magnetic hydrogels (HCFO) having high water content are prepared using the solvent casting method. The effective magnetic properties, such as coercivity and remnant magnetization of the hydrogels, are determined from the magnetization response (m-h curve) obtained through a vibrating sample Magnetometer (VSM). Subsequently, the HCFOs are subjected to uniaxial tensile loading to obtain mechanical properties. The size and shape of MNPs are obtained using X-ray Diffraction (XRD) and scanning electron microscopy (SEM) analysis. Furthermore, the magnetic hydrogel beams (cantilever) have been prepared and subjected to the external magnetic field. A unique phenomenological model has been proposed which can predict the finite deflection of the beam under magnetic loading exploiting the hard magnetic behavior of the HCFO. The proposed model takes into account particle concentration, finite elasticity, and magneto-mechanical coupling. The softness of the hydrogels matrix and hard magnetic properties of the MNPs results in large deflection. Further, the experimental observations and modeling predictions are in good agreement.

Magnetization reversal and coercivity mechanism in ferrimagnetic M-type hexaferrite by controlling phase evolution

The correlation of phase evolution (annealing at different temperatures) with magnetic properties like magnetization reversal, coercivity mechanism, and energy product in M-type hexaferrite by substituting Sr in place of Ba has been reported in the present article. The Ba1-xSrxFe12O19 (x = 0.0, 0.5, & 1.0) have been prepared by the sol–gel auto-combustion method followed by annealing at different temperatures from 800 °C to 1200 °C. The structural and magnetic properties have been characterized by X-ray diffraction, Field emission scanning electron microscopy, Raman spectroscopy, and Vibrating sample magnetometer. The Rietveld refinement confirms contraction in unit cell parameters by replacing Sr in place of Ba and lattice expansion with increasing annealing temperature. There is no significant effect of substitution on magnetic properties found rather heat treatment affects greatly. The transition from a single domain to multidomain particles and their contribution to initial magnetization curves are analyzed. The differential susceptibility (dM/dH) calculated from room temperature magnetization confirms the existence of a pinning effect during magnetization reversal for samples heat treated below 1200 °C. Secondary phases or grain boundaries are believed to act like pinning centers. This work opens insight into the domain wall motion by microstructure engineering. The coercivity is tuned to 6.09 kOe by controlling the annealing temperature for the Ba1-xSrxFe12O19 (x = 1.0) sample. The maximum energy product (BH)max in the range of 0.94–1.27 MGOe has been achieved.

Flexible and twistable free-standing PDMS-magnetic-nanoparticle-based soft magnetic films with robust magnetic properties

In this paper, we develop multifunctional, physically soft, mechanically compliant, and magnetically responsive PDMS films, with embedded Fe3O4 nanoparticles, that show robust magnetic properties over a significant range of mechanical deformation. First, we establish that the magnetic properties, namely the saturation magnetization (M s), remanent magnetization (M r), and intrinsic coercivity (H ci) of these PDMS films in highly deformed configurations, i.e. in folded, twisted (with different twist angles), and bent (flexed) configurations, show very little degradation compared to those obtained in undeformed configurations. Next, the films were subjected to repetitive cycles of zero-to-max deformation (R = 0) and the saturation magnetization of the films was shown to not exhibit any significant degree of progressive degradation as a function of cyclic deformation history. These findings confirm the excellent robustness and cyclic durability of magnetic properties shown by these magnetic and compliant PDMS films and point to their suitability for wearable electronics applications.

Phase evolution, microstructure, and improved magnetic properties for off-stoichiometric SmFe12-based alloys

Low rare earth content and high intrinsic magnetic properties make SmFe12-based permanent magnets a potential candidate for NdFeB-based magnets in medium to high temperature environments. However, the easy formation of multiple ferromagnetic intergranular phases limits the preparation of high coercivity magnets. Composition optimization is an indispensable measure for the realization of high-performance magnets. In this work, off-stoichiometric composition design is employed to prepare SmFe12-based alloys. Ti is first introduced to inhibit the precipitation of α-Fe phase, obtaining a high coercivity of 484 kA/m, while the ribbon undergoes a reduction of remanence significantly. After regulating Fe–Co content to 11.5, the remanence recoveries from 0.51 to 0.65 T with a slight increase in coercivity (484–493 kA/m). Finally, Fe content is optimized to further improve magnetic properties, with both coercivity and remanence are improved simultaneously, reaching 509 kA/m and 0.70 T, respectively. Phase evolution, microstructure and their relationship with magnetic properties are investigated in detail. Micromagnetic simulation shows that the increased domain wall pinning effect induced by the refinement of grain size is the main reason for high coercivity. This work provides a feasible compositional design method for the preparation of high performance SmFe12-based alloys.