Magnetic Annealing Research Articles

Magnetic properties dependence on the coupled effects of magnetic fields on the microstructure of as-deposited and post-annealed Co/Ni bilayer thin films

Magnetic films and multilayers are the focus of much attention motivated mainly by their wide range of applications, such as magnetic data storage devices and sensors. The magnetic multilayer structures are normally prepared through physical means of deposition, as molecular beam epitaxy (MBE) or sputtering. However, there are already examples of materials produced by electrochemical routes, which share with the other deposition techniques a high sensitivity of magnetic and transport properties of the samples on their crystallographic and chemical structure. In addition, electrochemical deposition allows growing structures with high aspect ratio, which are not possible to obtain by MBE deposition followed by lithographic processes. The present work investigates the Co/Ni bilayered nanocrystalline films produced through the temperature-elevated electrochemical deposition, and modified by annealing carried out also under an external magnetic field. The results indicate an increase of the coercive field of deposited Co/Ni bilayers, when the electrodeposition process was conducted under magnetic field of 1T. The annealing processing caused further remarkable increase of the coercive field of as-prepared bilayers that has been preserved under magnetic annealing conditions. The magnetic properties are discussed in terms of samples microstructure. In as-prepared samples the in-plane magnetization was observed, while high temperature treatment, causing microstructural changes in the film, resulted also in appearance of a small component of magnetization oriented perpendicularly to the films’ plane that could have been observed by MFM analysis. The induced perpendicular magnetization component in the post-annealed samples was a result of the magnetic field applied in the perpendicular direction to the samples’ surface during annealing treatment.

High magnetostriction parameters for low-temperature sintered cobalt ferrite obtained by two-stage sintering

From the studies on the magnetostriction characteristics of two-stage sintered polycrystalline CoFe2O4 made from nanocrystalline powders, it is found that two-stage sintering at low temperatures is very effective for enhancing the density and for attaining higher magnetostriction coefficient. Magnetostriction coefficient and strain derivative are further enhanced by magnetic field annealing and relatively larger enhancement in the magnetostriction parameters is obtained for the samples sintered at lower temperatures, after magnetic annealing, despite the fact that samples sintered at higher temperatures show larger magnetostriction coefficients before annealing. A high magnetostriction coefficient of ~380ppm is obtained after field annealing for the sample sintered at 1100°C, below a magnetic field of 400kA/m, which is the highest value so far reported at low magnetic fields for sintered polycrystalline cobalt ferrite.

Magnetic domain characterisation of high magnetic field treated FeGa single crystal

Previous research has shown that stress annealing and magnetic field annealing can build uniaxial anisotropy into FeGa alloy to enhance saturation magnetostriction without preload. In this paper, we focus on the possibility of inducing uniaxial anisotropy in Fe81Ga19 single crystal by high magnetic treatment. The single crystal sample was grown by the Bridgman method and cut into an 8×5×5 mm cuboid with (001) planes determined by Laue backscattering. Both maze-like out of plane domains and true magnetic domains were obtained with magnetic force microscopy (MFM). The results indicate that magnetic domains were well aligned with the treating magnetic field. A reliable disparity of uniaxial anisotropy has been proved with the domain and domain wall width change in MFM patterns.

Magnetic assembly and annealing of colloidal lattices and superlattices.

The ability to assemble mesoscopic colloidal lattices above a surface is important for fundamental studies related with nucleation and crystallization but also for a variety of technological applications in photonics and microengineering. Current techniques based on particle sedimentation above a lithographic template are limited by a slow deposition process and by the use of static templates, which make difficult to implement fast annealing procedures. Here it is demonstrated a method to realize and anneal a series of colloidal lattices displaying triangular, honeycomb, or kagome-like symmetry above a structure magnetic substrate. By using a binary mixture of particles, superlattices can be realized increasing further the variety and complexity of the colloidal patterns which can be produced.

Microwave ferromagnetic properties of as-deposited Co2FeSi Heusler alloy films prepared by oblique sputtering

The Co2FeSi films are deposited on Si (100) substrates by an oblique sputtering method at ambient temperature. It is revealed that the microwave ferromagnetic properties of Co2FeSi films are sensitive to sample position and sputtering power. It is exciting that the as-deposited films without any magnetic annealing exhibit high in-plane uniaxial anisotropy fields in a range of 200 Oe–330 Oe (1 Oe = 79.5775 Am−1), and low coercivities in a range of 5 Oe–28 Oe. As a result, high self-biased ferromagnetic resonance frequency up to 4.75 GHz is achieved in as-deposited oblique sputtered films. These results indicate that Co2FeSi Heusler alloy films are promising in practical applications of RF/microwave devices.

Enhancing Coercivity of Sintered Nd-Fe–B Magnets by Nanoparticle Addition

In this paper, we investigated the influence of addition of Dy <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">40</sub> Nd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">40</sub> Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">30</sub> nanoparticles on the structure and magnetic properties of sintered Nd-Fe-B magnets. The nanoparticles with a size smaller than 50 nm were prepared using high-energy ball milling method and then mixed with micrometer Nd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sub> B powder before magnetic anisotropic pressing, vacuum sintering, and annealing. The structure of the magnets was thoroughly analyzed using X-ray diffraction and electron microscopy techniques. The magnetic properties of the magnets were investigated on a pulsed field magnetometer. The atoms of Dy were detected mainly at the grain boundaries and partly in the near-boundary area of the grains. On adding 2% of the nanoparticles, the coercivity of the magnets is enhanced by quite a large amount, from 12 kOe for the unadded magnets to 21 kOe for the added ones. The large increase of the coercivity is probably due to the diffusion of Dy to the Nd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sub> B grains to form (Nd,Dy) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sub> B phases with high magnetocrystalline anisotropy. The nanoparticles might make Dy distribute more homogeneously and diffuse to the Nd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sub> B grains more efficiently.

Effect of Magnetic Annealing on IrMn Based Spin Valve Materials with SAF Structure

Effect of Magnetic Annealing on IrMn Based Spin Valve Materials with SAF Structure

Post magnetic field annealing effect on magnetic and structural properties of Co80Pt20 nanowires and nanotubes fabricated by electrochemical method

Highly ordered Co80Pt20 nanowires (NWs) and nanotubes (NTs) have been synthesized by low cost DC electrochemical deposition method with constant stirring during the fabrication process in anodic aluminum oxide nano-templates with average pore diameter of about 200 nm. The structural and magnetic properties of nanostructures have been investigated before and after simple and magnetic field annealing. Magnetic field of 1 T has been applied during annealing process in the direction perpendicular to NWs and NTs axis. X-Ray Diffraction analysis shows face centered cubic (fcc) as the dominant phase for Co80Pt20 NWs and post annealing led to better crystallinity with retained fcc phase. Furthermore, magnetic properties, including saturation magnetization (Ms), squareness ratio (Mr/Ms), and coercivity (Hc), have been investigated as a function of annealing temperature by Vibrating Sample Magnetometer.

Three-Dimensional Nanoelectrode by Metal Nanowire Nonwoven Clothes

Metal nanowire nonwoven cloth (MNNC) is a metal sheet that has resulted from intertwined metal nanowires 100 nm in diameter with several dozen micrometers of length. Thus, it is a new metallic material having both a flexibility of the metal sheet and a large specific surface area of the nanowires. As an application that utilizes these properties, we propose a high-cyclability electrode for Li storage batteries, in which an active material is deposited or coated on MNNC. The proposed electrode can work without any binders, conductive additives, and current collectors, which might largely improve a practical gravimetric energy density. Huge electrode surfaces provide efficient ion/electron transports, and sufficient interspaces between the respective nanowires accommodate large volume expansions of the active material. To demonstrate these advantages, we have fabricated a NiO-covered nickel nanowire nonwoven cloth (NNNC) by electroless deposition under a magnetic field and annealing in air. The adequately annealed NNNC was shown to be an excellent conversion-type electrode that exhibits a quite high cyclability, 500 mAh/g at 1 C after 300 cycles, compared to that of a composite electrode consisting of NiO nanoparticles. Thus, the present design concept will contribute to a game-changing technology in future lithium ion battery (LIB) electrodes.

Effect of magnetic field annealing and size on the giant magnetoimpedance in micro-patterned Co-based ribbon with a meander structure

Micro-patterned Co-based amorphous ribbons (Metglas® 2714A) with a meander structure are fabricated by MEMS technology and the giant magnetoimpedance (GMI) effects are measured at different magnetic fields and frequencies. The effect of magnetic field annealing and size (line width and line length) on the GMI effect is investigated. It is found that the GMI effect in the transverse magnetic field-annealed state is larger than that in longitudinal magnetic field-annealed state and nonfield-annealed state. The maximum GMI effect increases from 82 % for the sample with 5 mm length to 150 % for the sample with 10 mm length, and the maximum GMI effect decreases with the increase of the line width.

Influence of Magnetic Field Annealing on Magnetic Properties for Nanocrystalline $({\rm Fe}_{0.5}{\rm Co}_{0.5})_{73.5}{\rm Cu}_{1}{\rm Mo}_{3}{\rm Si}_{13.5}{\rm B}_{9}$ Alloy

Influence of magnetic field annealing on room- and high-temperature magnetic properties of nanocrystalline (Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> ) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">73.5</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> Mo <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13.5</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</sub> alloy was investigated. The initial permeability (μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</sub> ) of nonmagnetic annealed samples decreases with annealing temperature (T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</sub> ) increasing, while the μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</sub> of magnetic annealed samples increases with T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</sub> . In contrast to the nonmagnetic annealing samples, the saturation magnetostriction (λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</sub> ) of magnetic annealed samples decreases with Ta increasing because of the ordered rearrangement of the magnetic domain along the applied field direction. Meanwhile, magnetic annealing can induce a uniaxial anisotropy, which results in the enhancement of effective magnetic anisotropy (<;K>). The change of λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</sub> and can be used to interpret the temperature dependence of initial permeability (μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</sub> -T curves) for nanocrystalline alloys.

Enhancement of exchange bias and training effect in ion-beam sputtered Fe46Mn54/Ni81Fe19 bilayers

We present a remarkable enhancement by 300% of the exchange-bias field at room temperature, without affecting the coercivity value, via optimum magnetic annealing (250 °C/3 kOe) in ion-beam sputtered FeMn(30 nm)/NiFe(10 nm) bilayers. This specific behavior has been attributed to a higher degree of γ-FeMn(111) orientation that offers more interfacial FeMn moments to get pinned with the moments of the adjacent NiFe layer. Unlike the absence of training effect at room temperature, a pronounced training effect and an accompanying magnetization reversal asymmetry are evidenced upon field cooling below 50 K due to the presence of biaxial exchange induced anisotropy across the interdiffused FeMn/NiFe interface. The present findings not only have technological significance but also are of relevance to the understanding of interfacial spin disorder and frustration in these exchange-biased systems.

Magnetic annealing of the ion-beam sputtered IrMn/CoFeB bilayers – positive exchange bias and coercivity behaviour

The effect of optimum dilution of antiferromagnetic (AF)/ferromagnetic (FM) interface necessary for observance of positive exchange bias in ion-beam sputtered Si/Ir22Mn78 (tAF = 12, 18, 24 nm)/Co20Fe60B20(tFM = 6,9,15 nm) exchange coupled bilayers is investigated by magnetic annealing at 380, 420 and 460 °C for 1 h at 5 × 10-6 Torr in presence of 500 Oe magnetic field. While the coercivity of the exchange coupled FM layer decreases with the increase in annealing temperature irrespective of the value of tAF or tFM, the hysteresis loops however shift by ≈+ 10 Oe whenever the coercivity drops in the 10–15 Oe range. This is consistent with the phase diagram of exchange bias field and coercivity derived from Meiklejohn and Bean model. The X-ray diffraction and X-ray reflectivity measurements confirmed that the texture, grain size and interface roughness of IrMn/CoFeB bilayers are thickness dependent and are correlated to the observed magnetic response of the bilayers. The results establish that optimum dilution of the IrMn/CoFeB interface by thermally diffused Mn-spins is necessary in inducing the effective coupling between the IrMn domains and diluted CoFeB layer. It is further shown that the annealing temperature required for the optimum dilution of the CoFeB interface critically depends on the thickness of the layers.

Bulk Permanent Magnet with Enhanced Anisotropy Fabricated by Magnetic Annealing from Fe-B-Nd-Nb Bulk Metallic Glass Precursor

Fe68.16B20.16Nd7.68Nb4bulk metallic glass was annealed at 973 K for 15 min with or without external magnetic fields. The maximum energy product (BH)maxmeasured along the axial direction of a rod sample after annealed with a magnetic field parallel to the axis is 10.9 % higher than that annealed with a perpendicular field. The intrinsic coercivityiHcof the sample annealed with the parallel magnetic field reached 1014 kA/m. The induced magnetic anisotropy is attributed to the formation of preferred crystallographic orientation of ferromagnetic phases under the external magnetic field.

Chemical Bath Deposition of ZnS Buffer Layers

Chemical bath deposited ZnS thin films are promising buffer layers for thin film solar cells, replacing the environmentally hostile CdS buffer layers currently in use. Reflection, absorption and scattering are the three main light loss mechanisms in buffer layers. In this work, improved process conditions, such as magnetic stirring and air annealing, are used in the chemical bath deposition of ZnS thin films to optimize their surface morphology, which effectively reduces light scattering and increases the transmittance, resulting much better ZnS thin films.

Enhanced magnetostriction of a narrow hysteresis Tb0.26Dy0.54Ho0.20Fe2 alloy

In this work, a magnetic annealing method used to enhance the magnetostrictive property of a narrow hysteresis alloy Tb0.26Dy0.54Ho0.20Fe2 is reported. Cylindrical-rod shaped specimen with 〈110〉 crystal orientation was fabricated using zone-melting unidirectional solidification technique, followed by annealing in a transverse magnetic field of 366 kA/m. The crystal orientation and bi-phase solidified morphology can be retained after magnetic annealing. A high magnetostriction of 1.508×10−3 was obtained in the magnetically annealed specimen, which is 25.2% larger than the untreated one. Simultaneously, the magnetostriction hysteresis width is slightly enlarged from 4.45 to 6.36 kA/m, which is still much lower than that of the Ho-free Tb0.3Dy0.7Fe2 alloy. The additional anisotropy which is induced by magnetic annealing, as reflected by the magnetic hysteresis loops, is responsible for the enhancement of magnetostrictive performance.

High magnetostriction coefficient of Mn substituted cobalt ferrite sintered from nanocrystalline powders and after magnetic field annealing

Magnetostriction characteristics of Mn substituted cobalt ferrite, CoFe2−xMnxO4 (0 ≤ x ≤ 0.3), sintered from nanocrystalline powders of average particle size of ∼4 nm have been studied. Larger value of magnetostriction at lower magnetic field is achieved after substitution of Mn for Fe. The maximum value of magnetostriction coefficient is not much affected and the slope of the magnetostriction is increased with increasing Mn content. Higher maximum value of magnetostriction coefficient (λ) of 234 ppm comparable to that of the unsubstituted composition with larger strain derivative (dλ/dH) is obtained for x = 0.2 in CoFe2−xMnxO4. The magnetostriction coefficient is increased to 262 ppm with further enhancement in the strain derivative after annealing the sintered compact at 300 °C in a magnetic field of 400 kA/m for 30 min.

Magnetic annealing effects on the properties of multilayer BaTiO3/CoFe2O4 thin films

Multilayer BaTiO3/CoFe2O4 thin films are prepared via a chemical solution deposition method with and without magnetic annealing, respectively. The microstructural, magnetic, dielectric and ferroelectric properties of the films’ are investigated. The dielectric constant, polarization and magnetization of the multilayer thin films are improved with magnetic annealing. Moreover, for the magnetic annealing films, the saturation magnetization measured with the measuring magnetic field vertical to the film surface is much higher than that measured with the field parallel to the film surface. These novel phenomena may be caused by the decrease in the clamping of the BaTiO3 layer and the arrangement of the induced easy axis in the CoFe2O4 layer caused by the applied annealing field.

The Effect of Static Magnetic Field on Electroless Ni-P In Situ Deposition and Post-annealing

The influence of static magnetic field of 4 T on electroless Ni-P deposition process and post-annealing was investigated in this study. The results from differential scanning calorimeter have shown that the imposed high magnetic field during electroless deposition had a further beneficial effect on defects migration and annihilation after Ni-P alloys heated at around 250 °C. Furthermore, it is found that some metastable phases were presented after magnetic annealing at 300 °C (below crystallization temperature), and the hardness of magnetic-annealed Ni-P alloys was greater than that of conventionally annealed Ni-P alloys. The morphology of the Ni-P alloys was characterized by scanning electron microscope, and shows typical spherical nodular structure for the as-deposited Ni-P alloys. The boundaries of these spherical nodular crystals blurred after annealing; however, the boundaries were apparently observed after magnetic annealing at 300 °C.

Magnetic Annealing on GNO Electrical Steel Fe-3.25% Si

Grain non-oriented electrical steel has its main application in electrical motors and its microstructure significantly influences their efficiency. The objective of this work was to investigate whether or not magnetic field applied during annealing process affects grain growth and the development of important texture components leading to an improvement of the magnetic properties. GNO Fe-3.25%Si 75% cold rolled specimens were annealed inside magnetic field with strength of 17 T at the temperature of 800°C for 3, 10 and 30 minutes. Results of average grain size after magnetic annealing showed a microstructure formed by small grains and a few very large grains. Magnetic field did not increase orientation density of {100} oriented grains and Goss grains but was able to increase density of θ fiber and decrease the density of γ fiber.