Magnetic Annealing Research Articles

Microstructure Evolution and Grain Boundary Characteristics of Oriented Silicon Steel during Primary Recrystallization in a Pulsed Magnetic Field

The effects of a 2 T pulsed magnetic field primary annealing process on microstructure evolution and grain boundary characteristics in two-stage cold-rolled silicon steel were examined. Pulsed magnetic annealing increased grain size through the application of relatively smaller intensity of magnetic fields (2 T), compared to steady magnetic annealing. The effect of increasing grain size may be attributed to the magnetic acceleration effect of boundary motion under magnetic pulse conditions. Pulsed magnetic annealing may serve to enhance the relative intensity of the {111} component and decrease the frequency of low-angle misorientations. Repeated magnetostriction induced by pulsed magnetic field applications may accelerate overall dislocation motion. These findings suggest that pulsed magnetic fields require relatively lower intensities than steady magnetic fields to achieve superior results, providing a potentially viable alternative for industrial annealing processes for electrical steels.

Synthesis of bulk FeHfBO soft magnetic materials and its loss characterization at megahertz frequency

Magnetic core materials with low loss, high saturation magnetization, large permeability, and operating frequency above 1 MHz are in high demands for the next generation of miniaturized power electronics. Amorphous FeHfB ribbons with thickness around 20 μm have been fabricated through melt-spinning. Different heat treatments were performed on the FeHfB ribbons, and the relations among heat treatments, microstructure, and magnetic properties have been explored. Properties such as coercivity (Hc) of 2.0 Oe and saturation magnetic flux density (BS) of 1.2 T have been achieved in samples with exchange coupling. The losses can be minimized by balancing the hysteretic and eddy current losses and can be further reduced with additional magnetic field annealing. At 5 MHz with peak magnetic flux density of 20 mT, the materials show core losses comparable to the best ferrites, but with higher permeability value of about 200 and superior saturation induction of more than 1 T.

Effect of magnetic field annealing on magnetic properties for nanocrystalline (Fe1−xCox)78.4Si9B9Nb2.6Cu1 alloys

The crystalline volume fraction Vcry, saturation magnetostriction λs, effective magnetic anisotropy 〈K〉, and temperature dependence of initial permeability (μi-T curves) for magnetic and nonmagnetic annealed (Fe1−xCox)78.4Si9B9Nb2.6Cu1 (x = 0.35, 0.5, 0.65, 1) alloys were investigated. The results showed that the magnetic annealing can enhance the Vcry and significantly reduce the λs. The Co content has an obvious effect on the λs and 〈K〉, the largest 〈K〉 was observed for the x = 0.5 magnetic annealed sample, which can be explained with magnetic atoms pair ordering theory. And the best high-temperature magnetic softness was obtained for x = 0.35 magnetic annealed sample, in which the lower λs and larger Vcry were observed.

The effect of magnetic annealing on the magnetostriction for Sm-Dy-Fe rod alloys

The Sm0.86Dy0.14Fex (x = 1.85−2.05) magnetostrictive alloys have been prepared with arc-melting and then cast into a copper mold with a diameter of 8 mm. It is found that the magnetostriction (λ// − λ⊥) increases from −900 × 10−6 for untreated rod alloys to −1200 × 10−6 for magnetically annealed rod alloys at the magnetic field of 640 kA/m. In the magnetic annealing temperature range of 483−643 K, the magnetostriction value exhibits a peak at 543 K. The variation of magnetostriction and magnetization with magnetic fields has been determined and the mechanism of domains' movements has been discussed. This result is very important to improve the magnetostrictive property of Sm-Dy-Fe rod alloys.

Enhanced Giant Magnetoimpedance Effect in Rapid Heat-Treated Fe-Based Amorphous Ribbons

An enhanced giant magnetoimpedance (GMI) effect of Fe-based amorphous ribbons is obtained by rapid heat treatment. The structural investigations on the ribbon reveal the presence of two phases, i.e. a fine grained Fe3Si phase and a residual amorphous phase on rapid heat treatment. The soft magnetic property is improved by rapid heat treatment; the crystal size and grain size of Fe3Si decrease. The maximum magnetoimpedance ratio obtained in the present study is 81% at 10 MHz, and the optimized heat-treated rate is 200°C/min. Separated GMI curves are observed after the simultaneous rapid heat treatment and magnetic field annealing. This suggests that tailoring of the nanocrystalline microstructures induced by optimum rapid heat treatment conditions can result in an excellent GMI effect.

Nanocrystalline electroplated NiFe‐based alloys for integrated magnetic microsensors

AbstractThe effect of pulse plating (PF) and direct current (DC) plating on the magnetic properties and grain size of electroplated NiFe films for the application in magnetic microsensors, i.e., as integrated magnetic concentrator, has been studied. In order to further improve magnetic properties additional subsequent thermal annealing experiments were carried out with chosen films. A sulphate‐based NiFe electrolyte containing various additives operated at a pH of 3.5 and a temperature of 50 °C was used. The softmagnetic NiFe films were deposited at a thickness of >10 µm on silicon substrates with a sputtered 200 nm thick Cu seed layer and a 50 µm high photoresist mould. The composition and magnetic properties were measured by energy dispersive X‐ray spectroscopy (EDX) and vibrating sample magnetometer (VSM), respectively. The morphology was investigated by X‐ray diffraction (XRD) and transmission electron microscopy (TEM). The composition of the fabricated fcc NiFe films ranged from 3 to 42 wt% Fe with a good adhesion. The as‐plated NiFe exhibited nanocrystalline grain sizes ranging from 12 to 18 nm with a coercivity as low as 16 A m−1. It was found that the grain size is generally higher at a lower iron content. However, pulse forward (PF) plating favours a refined grain size over DC plating which can be attributed to an increased nucleation rate caused by the high pulse current densities (high overpotential). By applying a thermal annealing for 2 h at 300 °C in a vacuum oven the coercivity of NiFe samples with ∼18.5 wt% Fe could be further reduced to 6 A m−1.

Influence of Annealing on Magnetic Performance for 1K107 Amorphous-Nanocrystalline Soft Magnetic Alloy

The morphology, microstructure and magnetic properties in 1K107 alloy annealed by nitrogen and transversal magnetic (N2) are studied. The results show that coercivity (Hc), remanence ratio (Br/Bs), core loss (Pc), and effective permeability (μe) are efficiently optimized by transversal magnetic annealing (N2) according to the methods of digital electric bridge, rectifier bridge, X-ray diffraction (XRD), and field emission scanning electron microscopy (FESEM), etc.

Influence of magnetic annealing on electrochemical performance of La0.67Mg0.33Ni3.0 hydride electrode alloy

A novel magnetic annealing assisted route was applied to improve the electrochemical properties of La0.67Mg0.33Ni3.0. The effects of magnetic annealing parameters, including annealing temperature, annealing time and magnetic induction density, on electrochemical performance of La0.67Mg0.33Ni3.0 hydride electrode alloys was investigated using L9 orthogonal array based on Taguchi method. Based on the analysis of signal to noise ratio and the variance, the optimum magnetic annealing parameters for La0.67Mg0.33Ni3.0 hydride electrode alloy are determined to be 1T, 1123K, and 2h. A confirmation test was conducted subsequently, and the results were found to be within the confidence interval. The discharge capacity, the cyclic stability and the electrochemical kinetics of the alloy electrode were noticeably improved by magnetic annealing.

Induced magnetic anisotropy in permalloy films annealed with magnetic field

The effect of magnetic annealing on Fe21Ni79 films was investigated through the characterization of crystal structure and magnetic properties. Fe21Ni79 films were deposited on thermally oxidized Si substrates using a DC magnetron sputter. A highly a-axis oriented Fe21Ni79 film was grown on Si substrate by magnetic annealing. Columnar grain growth was dominant in the films annealed with magnetic field. Both the area surrounded by hysteresis curve, and coercivity, were increased by magnetic annealing, indicating that the magnetic annealing induced the anisotropy energy. Through EXAFS analysis, 1.19×10−3 was obtained as the strain of a specimen annealed with magnetic field. This value confirmed that induced magnetic anisotropy was formed by atomic pair ordering.

Tailoring the Hysteresis Loop of the Si/Cu(10nm)/FeMn(10-30nm)/CoFeB(10nm) Bilayer System

The dependence of hysteretic properties of FeMn/CoFeB (AF/FM) thin bilayers on AF thickness and magnetic annealing temperature is systematically investigated for possible applications in spin-valve devices. Inducement of an easy axis after magnetic annealing is established. The anisotropy is studied by investigating the coercivity along and perpendicular to the induced easy axis using Magneto-Optic Kerr Effect (MOKE) and the AF texture is ascertained by XRD. The existence of an optimum annealing temperature, for which the maximum change in coercivity occurs for a particular AF thickness, is evidenced. The maxima in HC of the bilayer with thickness of AF layer were correlated with FCC FeMn (111) texture of the sample.

A novel experimental approach to determine the absolute grain boundary energy

The shape of a 90° ⟨112⟩ tilt boundary in bismuth and a boundary in zinc bicrystals was analyzed, which had developed during annealing at elevated temperatures when the boundary had migrated due to the magnetic free energy density difference across the boundary while the boundary was fixed on the lateral sample surfaces. After annealing in an external magnetic field the 90°⟨112⟩ boundary in bismuth became faceted. This evidenced the pronounced anisotropy of boundary energy with respect to its inclination. The random (non-tilt) boundary in the Zn bicrystal assumed a curved shape after magnetic annealing. Evaluation of the curvature of the boundary segments with the highest constant curvature permitted estimation of the upper limit of the energy of differently inclined boundary sections in Zn: 0.27 and 0.41 J m−2.

Soft magnetic properties of amorphous Fe52Co34Hf7B6Cu1 alloy treated by pulsed magnetic field and annealing

The crystallization, microstructure, and soft magnetic properties of Fe52Co34Hf7B6Cu1 alloy are studied. Amorphous Fe52Co34Hf7B6Cu1 alloys are first treated by a pulsed magnetic field with a medium frequency, and then annealed at 100 °C–400 °C for 30 min in a vacuum. The rise in temperature during the treatment by a pulsed magnetic field is measured by a non-contact infrared thermometer. The soft magnetic properties of specimens are measured by a vibrating sample magnetometer (VSM). The microstructure changes of specimens are observed by a Mössbauer spectroscopy and transmission electron microscope (TEM). The results show the medium-frequency pulsating magnetic field will promote nanocrystallization of the amorphous alloy with a lower temperature rise. The nanocrystalline phase is α-Fe(Co) with bcc crystal structure, and the grain size is about 10 nm. After vacuum annealing at 100 °C for 30 min, scattering nanocrystalline phases become more uniform, the coercive force and the saturation magnetization of the specimens are 41.98 A/m and 185.15 emu/g.

Induced additional anisotropy influences on magnetostriction of giant magnetostrictive materials

Initial magnetization realignments induced by a uniaxial compressive pre-stress or transverse magnetic annealing can enhance effectively strain output of giant magnetostrictive materials. However, differing from the use of stress that induces in-plane anisotropy, it is found that magnetic annealing is capable of resulting in a uniaxial magnetic anisotropy in 〈110〉 grain-aligned TbDyFe polycrystals. We find the critical induced additional anisotropy to generate a uniaxial magnetization alignment along only one easy axis that is essential to realize 90° domain evolution during initial magnetization stage, hence yielding a large magnetostriction under modest switching fields. By a phenomenological approach based on magnetization rotation, we explain quantitatively how the induced additional anisotropy energy influences the magnetostrictive behaviors under coupled magnetomechanical loadings. Consequently, distinctive approaches to further enhance the saturation magnetostriction are suggested through the combination use of induced additional anisotropy and compressive pre-stress.

Giant magnetoimpedance in thin amorphous wires: From manipulation of magnetic field dependence to industrial applications

Abstract We present the results on tailoring of soft magnetic properties and GMI effect in thin microwires paying special attention on achievement of low hysteretic high GMI effect in the extended frequency range (up to 4 GHz). We observed considerable dependence of the GMI ratio and magnetic anisotropy field, Hk, of Co-rich amorphous microwires with vanishing magnetostriction constant on the internal and applied stresses. For low magnetostrictive Co-rich composition we obtained microwires low coercivity values (generally below 10 A/m). Field dependence of the off-diagonal voltage response measured in pulsed regime (pulsed GMI) exhibits anti-symmetrical shape. The magnetic anisotropy of Co and Fe-rich microwires can be tailored by stress or magnetic field annealing. Particularly stress annealed Fe-rich microwires exhibit stress-sensitive GMI effect and hysteretic properties. Varying the time and the temperature of such stress annealing we are able to tailor both magnetic properties and GMI. Additionally, magnetic response of linear microwires arrays and GMI effect of the system containing few microwires can be tailored through the magnetostatic interaction between the microwires. We found, that if the surface anisotropy is not circumferential, then the MI curve Z(H) presents hysteresis. This hysteresis can be suppressed by application of sufficiently high DC bias current IB that creates a circumferential bias field HB.

Vacuum chamber made of soft magnetic material with high permeability

In particle accelerators, a very effective way to shield an external magnetic field, which affects the beam inside the vacuum chambers, is to manufacture the vacuum chambers using soft magnetic materials with high permeability. We selected a permalloy and a ferritic stainless steel as candidates of those magnetic materials. However, until now the vacuum performance of vacuum chambers made of magnetic material does not yet have a proven track record.Therefore we made a list of items to be examined and verified. These items are listed as follows.1.General vacuum performance of the magnetic materials.2.Magnetic annealing condition and its effect on each performance.3.Magnetic and vacuum characteristic of a vacuum chamber made of soft magnetic material.The outgassing rate of the magnetic materials was equivalent to that of an austenitic stainless steel. A good magnetic shielding performance is obtained by annealing at higher temperatures than 850°C for both magnetic materials, although the performance declines, if the annealing temperature is too high. Furthermore the magnetic annealing in good vacuum is combined with vacuum heat treatment. The TDS spectrum showed that the reduction of hydrogen outflux from the bulk material near the surface was achieved by this process. Finally, we successfully produced a vacuum chamber with such a magnetic material, which will be used in a beam line at the 3GeV J-PARC synchrotron, because satisfying magnetic shielding and vacuum performance were obtained.

In situ magnetic annealing effects on multiferroic Mn-doped BiFeO3 thin films

BiFe0.95Mn0.05O3 thin films are prepared by chemical solution deposition with in situ magnetic annealing process. The effects of magnetic annealing on the microstructure, magnetic and dielectric as well as ferroelectric properties of the films are investigated. Increasing annealing magnetic fields, the crystallization quality is enhanced due to improved grain growth. Moreover, the leakage current decrease, and the magnetizations dramatically increase with increased annealing magnetic field, which is beneficial for the potential applications.

High magnetostriction and coupling coefficient for sintered cobalt ferrite derived from superparamagnetic nanoparticles

High magnetostriction (λ) and coupling coefficient (dλ/dH) of 315 ppm and 1.97×10−9 A−1m, respectively, are obtained at room temperature for sintered cobalt ferrite derived from nanocrystalline powders. Also, the powder was compacted at a low pressure of 8 MPa and sintered for a short duration of 10 min at 1450 °C. Magnetic annealing at 300 °C in a field of 0.5 T for 30 min further enhanced the magnetostriction coefficient to 345 ppm with a higher coupling coefficient 2.12×10−9 A−1m. The magnetic field above which maximum magnetostriction is observed is reduced by almost half after magnetic annealing.

Positive Exchange Bias in Ion-Beam Sputtered IrMn/CoFeB System Grown on CoFe Seed Layer

/CoFe/IrMn/CoFeB trilayers without any “eld cooling protocol. Theappearance of positive exchange bias is attributed to the antiferromagnetic coupling between theuncompensated Mn and ferromagnetic (FM) CoFeB spins at the interface. PEB in our sample isobtained as a consequence of interfacial microstructure control leading to unidirectional exchangeanisotropy, brought about by the incident energetic atoms/ions produced during ion-beam sputter-ing. On magnetic annealing, enhancement in the coercivity and disappearance of exchange bias isobserved irrespective of IrMn (111) textured growth due to the irreversible changes in the interfacialspin structure. The coercivity of CoFeB layers can be tuned by varying the seed layer thickness inthe magnetically annealed samples. The signi“cance of this work is a new insight into the effectof incident energetic atomic ”ux on the interfacial microstructure leading to positive exchange bias.Moreover, this study is promising in paving way for the utilization of trilayer stack with independentlyswitchable FM layers in CoFeB based TMR and GMR structures.

Improved leakage current and ferromagnetic properties in magnetic field annealed BiFeO3-based ceramics

Single-phase Bi0.85La0.15FeO3 ceramics were synthesized under various magnetic fields (Ha=0T, 3T, 5T). Substantially reduced leakage current and hence modified ferroelectric (FE) properties were obtained with magnetic field annealing (MA). The largest magnetization and lowest leakage current with large FE polarization (Pr∼33μC/cm2) were found in the sample annealed with Ha=3T. Great changes were also observed in the Raman spectra. All the observed features originate mainly from the different FE domain wall structures induced by MA. These results demonstrate that MA is an effective way to tune the multiferroic and magnetoelectric properties in BiFeO3-based materials.

Soft magnetic thin films: influence of annealing on magnetic properties

Soft magnetic materials are currently used in a variety of applications in electrical machines, sensors and elements of devices. If prepared in thin film form, they can be applied to micro- and nano-patterned devices. However, with respect to ribbons and bulk materials, thin films of the same composition usually display worse soft magnetic properties, thus requiring suitable solutions to restore high permeability and low coercivity. In this review, the magnetic properties of thin films prepared by sputtering are presented. Several compositions of soft magnetic materials are investigated, including Co-Fe-Si-B, Fe-Cu-Nb-Si-B, Fe-Si-B, Fe-Co-Nb-Si-P-B, Fe-Zr-Nb-Cu-B. Their amorphous-to-crystallization processes are studied by means of furnace annealing and Joule heating. Hysteresis loops and magnetic domain imaging, together with structural techniques, are used to follow the effects of annealing, which include stress relaxation and crystallization. The effects of magnetic field annealing are investigated and discussed.