Magnetic Field Annealing Research Articles

A novel grain refinement of Ce-Fe-B magnets induced by magnetic field annealing

Magnetic field annealing-induced grain refinement usually occurs during the crystallization process of amorphous alloys. This work investigates the effects of magnetic field annealing on the microstructure and magnetic properties of crystalline Ce17Fe76Co1Zr0.5B6Mo0.5 alloys. The results indicate that magnetic field annealing below the Curie temperature (TC) of the Ce2Fe14B phase in the alloys reduces the alloy’s grain size. At an annealing temperature of 433 K, the average grain size of alloys decreased from 48.0 nm in the as-spun sample to 27.2 nm in the magnetic field annealing sample. Moreover, magnetic field annealing can effectively reduce the volume fraction of the CeFe2 phase in the alloy. After magnetic field annealing at 433 K, the alloy obtained the optimal comprehensive magnetic properties: the intrinsic coercivity (Hci = 441.1 kA/m), remanence (Br = 0.49 T), squareness (Hk/Hci = 0.53), and maximum energy product ((BH)max) = 35.5 kJ/m3), which were 0.2 %, 16.7 %, 6 %, and 29.1 % higher than the values of the as-spun sample, respectively. Precession electron diffraction (PED) analysis revealed that magnetic field annealing increased strain at grain and phase boundaries and a more uniform grain orientation spread (GOS), promoting recrystallization and grain refinement. This study provides new insights into the grain refinement mechanism of crystalline alloys under magnetic field annealing, contributing to further improving the magnetic properties of Ce-Fe-B magnets.

Achieving constant magnetic permeability in Fe-based nanocrystalline alloys by Ni alloying and magnetic-field annealing for high DC bias capability and low coercivity

Achieving constant magnetic permeability in Fe-based nanocrystalline alloys by Ni alloying and magnetic-field annealing for high DC bias capability and low coercivity

Refining Alnico 8 magnets with composition optimization of matrix phase, directional solidification and magnetic field annealing

Optimized shape anisotropy of the Fe-Co rich ferromagnetic (α1) phase and the effective separation of the α1 and α2 phases with maximum magnetization difference—where α2 represents a paramagnetic magnetic phase—are the key parameters for maximizing the magnetic properties of Alnico magnets. In this manuscript, efforts have been undertaken to optimize the shape anisotropy of the α1 phase and increase the difference in magnetization and separation between α1 and α2 phases by fine tuning Al and Ni contents, directional solidification and magnetic field annealing methods. At first, Alnico magnets were fabricated by adjusting the content of α2 phase followed by homogenization, magnetic field annealing at high temperature, and low-temperature tempering. Intrinsic coercivity (Hcj) of ⁓146.0 kA/m, remanence (Br) of ⁓0.90 T and maximum energy density ((BH)max) of 46.02 kJ/m3 are achieved in the magnet with 8.2 wt% Al and 12.8 wt% Ni treated in field of 1.5 T for 10 minutes. At the second stage, the magnet with optimal magnetic properties is directionally solidified to develop columnar grains, and then the α1 phase is grown in the direction of the columnar grains by magnetic field annealing to enhance the (BH)max to 79.8 kJ/m3. The axial ratio of the α1 phase increased significantly with the increase of the grain size, particularly in the directionally solidified magnets. The Curie temperature of the α1 phase is noted near 1150 K, while the Curie temperature of the α2 phase is below 400 K. The magnets demonstrated excellent temperature stability, with magnetic properties decreasing by only 10–12 % at 800 K. These results may pave the way for further development of Alnico magnets specifically for high temperature applications.

Improving the Mechanical and Magnetic Properties of Equiatomic FeCo-2V Alloy Through Mild Magnetic Field Annealing

Improving the Mechanical and Magnetic Properties of Equiatomic FeCo-2V Alloy Through Mild Magnetic Field Annealing

Magnetostrictive strain-sensitivity synergy for laser-beam powder bed fusion processed Fe81Ga19 alloys by magnetic field annealing

Magnetostrictive Fe–Ga alloys have been demonstrated potentialities for numerous applications, whereas, suffering a tradeoff between large magnetostrictive strain and high sensitivity. Herein, bulk polycrystalline Fe81Ga19 alloys were prepared by laser-beam powder bed fusion (LPBF) and then annealed in magnetic field for manipulating the comprehensive magnetostrictive properties. Results indicate that <001> oriented grains are developed in the LPBF-prepared Fe81Ga19 alloys due to high temperature gradient. After magnetic field annealing (MFA), the magnetic domains within the alloys gradually transformed into well-arranged stripe domains, especially, flat and smooth 90° domains were established in the alloys annealed at 2600 ​Oe. As a result, the induced <001> orientation grains and 90° domains contributed to an improved effective magnetic anisotropy constant (57.053 ​kJ/m3), leading to an enhanced magnetostrictive strain of 92 ​ppm. Moreover, the MFA-treated alloys also displayed enhanced magnetostrictive sensitivity (0.097 ​ppm/Oe) owing to the smooth domain structures and low dislocation densities, demonstrating a fruitful strain-sensitivity synergy. In addition, good magnetostrictive dynamic response and enhanced compressive yield strength were also observed for the prepared alloys. This work demonstrates that LPBF and MFA might be an attractive strategy to resolve the tradeoff between strain and sensitivity, providing a basis for the preparation of high-performance magnetostrictive materials.

Improved High Frequency Soft Magnetic Properties in FeSiBCuNb Nanocrystalline Alloys Induced by Additional Low Magnetic Field Annealing

Improved High Frequency Soft Magnetic Properties in FeSiBCuNb Nanocrystalline Alloys Induced by Additional Low Magnetic Field Annealing

The influence of exchange-bias on the resonance frequencies and damping in IrMn3/[Co/Pt] multilayers

In order to realise single on-chip three axis magnetic field sensing technology without the need for convoluted die stacking, perpendicular media must be exploited. This poses additional challenges in both static-bias and the dynamics of the stack. Presented here are ferromagnetic resonance measurements (FMR) on exchange-biased multilayers of IrMn3/[Co/Pt]n. We chart the evolution of the different anisotropies caused by both magnetic field annealing and increasing repetition number n. The damping of these stacks does not obey the usual symmetry seen in single and bilayer samples with in-plane anisotropy, but instead follows a sin2(θ) dependence. This, we propose, is entirely dominated by spin diffusion from the Co layers into the adjacent heavy metal layers. This is modelled using a simple effective circuit model, providing a guide for the optimisation of complex multilayers.

Effects of Non-field Annealing and Magnetic Field Annealing on the Soft Magnetic Properties of Ni-Doped FINEMET Cores

Effects of Non-field Annealing and Magnetic Field Annealing on the Soft Magnetic Properties of Ni-Doped FINEMET Cores

Obtaining extremely low coercivity of high Bs FeCoBSiCPCu nanocrystalline alloys through modulation of magnetic anisotropy

Longitudinal magnetic field annealing is utilized for modifying the magnetic anisotropy and enhancing the magnetic softness of Fe75Co8(B10Si3C3P1)1-x/17Cux (x = 0.5, 0.75, 1, 1.25) nanocrystalline alloys. All of the magnetic field-annealed nanocrystalline alloys with Cu content more than 0.5 at.% exhibit significantly improved soft-magnetic properties, including high saturation magnetic flux density up to 1.87 T, effective permeability of 13,000–16,000 under the condition of 1 A/m and 1 kHz, coercivity as low as 1.6 A/m, and core loss of 0.11–0.45 W/kg under the condition of 1.0 T and 50 Hz. The application of a magnetic field promotes the nucleation and inhibits the growth of grains, leading to an increase in the number density of nanocrystals and the crystalline volume fraction, and a reduction in the grain size. The magnetic field annealing reduces the effective magneto-crystalline anisotropy energy to 2–4 J/m3, and induces longitudinal magnetic anisotropy with anisotropy energy density of 400–900 J/m3 which shows dependence on the crystalline volume fraction. The field-induced magnetic anisotropy dominates over the random local magnetic anisotropies, and results in the formation of regular magnetic domains aligned longitudinally, pinning-free domain wall displacement, and thus enhanced soft-magnetic properties.

Investigation of Magnetic Field Annealing of Amorphous Magnetic Material by using Permanent Magnets

Investigation of Magnetic Field Annealing of Amorphous Magnetic Material by using Permanent Magnets

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.

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.

Industrial-scale fabrication of FeSiBC cores with balanced soft magnetic properties by transverse magnetic field annealing and mixing of carbonyl iron powder

In this study, the effects of transverse magnetic field annealing and mixing fine powder on the soft magnetic properties of FeSiBC soft magnetic powder cores (SMPCs) are investigated. The results show that with the increase of transverse magnetic field intensity, the core loss of FeSiBC SMPCs decreases and then increases with a continuous increase in permeability compared to the zero magnetic field treatment. Wherein, the effective permeability of the powder cores is increased from 58.07 to 59.63 after transverse magnetic field annealing at a magnetic field intensity of 900 Gs and annealing temperature of 430 ℃. It shows that mixing the FeSiBC amorphous crushed powder with fine powder and transverse magnetic field annealing are effective ways to further promote amorphous SMPCs to meet the requirements of the development of electronic devices, and the prepared high-performance SMPCs also have a certain prospect of industrial application.

Magnetic properties of the amorphous Co-Fe-Cr-Si-B alloy after annealing in unsaturated magnetic field

The regularities of influence of temperature and intensity of a longitudinal magnetic field significantly less than the saturation field during annealing on the magnetic properties of an amorphous soft magnetic alloy based on Co have been studied. The possibility of the effectiveness of such treatment in comparison with traditional annealing without a field due to partial or complete suppression of stabilization of domain boundaries because of directional ordering is demonstrated. Annealing at temperatures below the Curie point with the application of unsaturated field exceeding the saturation field of the residual induction of an amorphous alloy in as-quenched state (40 A/m) showed the greatest efficiency compared with annealing without a field in terms of simultaneously reducing the coercive force Hc and increasing the low-field permeability µ0.3 and maximum permeability µmax. In comparison with non-field annealing, depending on the conditions of unsaturated magnetic field annealing, the possibility of reducing Hc by 39 %, increasing µmax by 4.5 times and µ0.3 by 3.8 times is shown. After annealing in unsaturated field on the magnetization curve of the alloy Co69Fe3.7Cr3.8Si12.5B11, the perminvar region, as well as the parabolic region where Rayleigh's law is fulfilled, end in lower fields than after annealing without a field. The results obtained are discussed taking into account the occurrence of various physical processes in the alloy during heat treatment.

Effect of Field Annealing on Magnetic Properties of Magnetic Soft Iron–Germanium Alloys

Abstract—The concentration dependence of the magnetic properties of iron–germanium alloys before and after thermomagnetic treatment, which represents an annealing of alloy samples in the ferromagnetic state in a permanent or alternating magnetic field (magnetic field annealing – MFA), has been investigated. It is shown that before MFA, with an increase in the germanium content in the range of 3–30 at % Ge, the coercive force increases and the residual induction decreases. As a result of thermomagnetic treatment, in the alloy samples magnetic anisotropy is induced: the magnetic hysteresis loops become narrower, the residual induction increases, and the coercive force decreases. Thermomagnetic treatment is effective for Fe–Ge alloys with a germanium content from 6 to 18 at %, and its highest efficiency is observed at 12 at % Ge. Features of the structural state of iron–germanium alloys and their role in the formation of magnetic properties during annealing in a magnetic field are discussed.

Effect of Magnetic Field Annealing on the Magnetic Properties of Soft-Magnetic Iron–Germanium Alloys

Effect of Magnetic Field Annealing on the Magnetic Properties of Soft-Magnetic Iron–Germanium Alloys

Spin Orbit Torque Locally Controlling Exchange Bias to Realize High Detection Sensitivity of Two-dimensional Magnetic Field

Spin orbit torque (SOT) of spin current has provided an efficient manipulation of ferromagnet order, antiferromagnet order, and exchange bias field for various spintronic applications. Here, in contrast to the external magnetic field which is very hard to apply locally, we propose to utilize the local control characteristic of SOT on the macro-nano-meter scale to set four different directions of exchange bias field at the IrMn/CoFe interface on one chip simultaneously. Moreover, with this fully electrical control technology to replace the existing various complex processes based on magnetic field annealing, we fabricate monolithic dual-axis full Wheatstone-bridge magnetoresistance sensors to detect two-dimensional magnetic field vector, which exhibit very high detection sensitivity of 9.45 nT·Hz−1/2 and 12.3 nT·Hz−1/2 at 10 Hz for X-axis and Y-axis sensing, respectively. This work provides a paradigm to simultaneously implement function configurations of spintronic devices by using the local control characteristic of SOT.

Effects of magnetic field annealing on the hard magnetic properties of milled Nd-Fe-B powders

In this study, we report the effect of magnetic field annealing (MA) in relieving the stress induced during the milling of Nd-Fe-B sintered magnets. The effect of MA processing parameters and particle size on the magnetic properties were investigated. Based on the results, magnetic field annealing is more effective in improving the magnetic properties of larger size particles, compared to finer particles. Our computational study on the role of particle surface defects in bimodal particle distribution agrees with results obtained experimentally. Magnetic field annealed powder has been successfully used to develop 4.6 g.cm−3 density bonded magnets with 75 vol% of magnetic powder and polyamide 12 (nylon 12) polymer binder resulting in 11.3 MGOe energy product.

Magnetic anisotropy instability due to magnetic field annealing in Ta/MgO/NiFe/MgO/Ta anisotropic magnetoresistive sensors

Ta/MgO/NiFe/MgO/Ta anisotropic magnetoresistive thin film sensors, which can be used for magnetic scales, were prepared. To improve the magnetoresistance ratio of the sensors, these sensors were vacuum-annealed with the magnetic field applied, and then, both the static and dynamic magnetoresistive responses of the sensors were obtained. The experimental results have shown that the instability of magnetic anisotropy occurs in the sensors after vacuum-annealing, leading to the significant hysteresis and abnormal output voltage peaks. To investigate the underlying physics, the distribution of the non-uniform demagnetizing field along the width of an anisotropic magnetoresistive (AMR) strip is considered, and both the static and dynamic responses of the AMR elements have been calculated on the basis of the Stoner–Wohlfarth model. The results have shown that the calculated results are in good agreement with the experimental data. The calculated results have revealed that the angles between the anisotropic field and the external magnetic field are different during the field cyclings of Hmax (maximum magnetic field) to −Hmax and −Hmax to Hmax. The angle difference is up to 6°, leading to different magnetoresistive responses. This paper is helpful for the understanding about the magnetization rotations in magnetic sensors and the manufacturing of sensors.

Effect of magnetic field annealing on magnetic properties and corrosion resistance of MnBi alloy

Herein, MnBi alloys are prepared using melt spinning and magnetic-field annealing techniques, and the effects of magnetic-field annealing on the microstructure, magnetic properties, magnetisation behaviour, and corrosion resistance of MnBi are systematically investigated. The results show that the saturation magnetisation (Ms) of the Mn55Bi45 ribbons increases with increasing magnetic field annealing temperature and time. Annealing above Curie temperature (Tc) enhances the intrinsic coercivity (Hcj) of the MnBi alloy. Moreover, Mn55Bi45 ribbons with a (BH)max of 2.15 MGOe at room temperature are successfully fabricated after annealing at 673 K for 20 min. The first-order reversal curve (FORC) demonstrate that the Mn55Bi45 ribbons after magnetic-field annealing exhibits weaker exchange coupling compared with the Mn55Bi45 ribbons after nonmagnetic-field annealing. Additionally, the corrosion rate of the Mn55Bi45 ribbons after magnetic-field annealing is lower than that of the Mn55Bi45 ribbons after nonmagnetic-field annealing. Finally, the changes in the grain size and content of the MnBi phase are investigated.