Magnetic Annealing Research Articles

The effects of field annealing on the magnetic properties of FeSiB amorphous powder cores

The effects of transverse magnetic field annealing on the magnetic properties of Fe78Si9B13 amorphous powder cores were investigated. The cores annealed at 400°C under an external transverse magnetic field of 0.5 T show an enhanced and stable effective permeability of 90 in the high frequency range up to 2MHz. Meanwhile, the permeability was improved by about 5% and the core loss was decreased by about 10% compared to the core with zero field annealing, which is attributed to the relief of internal stress and the variation of domain structure. It also shows superior DC bias property with a “percent permeability” of 70% at an external field of 100Oe. Transverse magnetic field annealing is an effective way to improve the soft magnetic properties of the amorphous powder cores. The improvement of soft magnetic properties of the Fe-based amorphous powder cores is encouraging for future applications as functional materials.

Effect of Magnetic Field Annealing on Microstructure and Magnetic Properties of FeCuNbSiB Nanocrystalline Magnetic Core with High Inductance

Effect of Magnetic Field Annealing on Microstructure and Magnetic Properties of FeCuNbSiB Nanocrystalline Magnetic Core with High Inductance

Reduced magnetic coercivity and switching field in NiFeCuMo/Ru/NiFeCuMo synthetic-ferrimagnetic nanodots

The coercivity (Hc) and switching field (Hsw) of free layers increase remarkably with shrinking structural dimensions, reducing the sensitivity of nanosized magnetoresistive sensors. In this work, conetic-alloy (NiFeCuMo) synthetic ferrimagnetic (SyF) trilayers are proposed to reduce Hc and Hsw in magnetic nanostructures. SyF stacks of NiFeCuMo/Ru/NiFeCuMo were patterned into nanodot arrays with diameter of 60nm by nanosphere lithography. The thickness of Ru layer was chosen so that high interlayer coupling energy existed in the continuous film. The linear dependence of Hc and Hsw of SyF nanodot on the amplification factor was revealed. Magnetic field annealing was conducted at various temperatures (Tan) ranging from 373K to 673K. Annealing at low temperature (Tan≤473K) relaxed the structural disorders, resulting in reduced surface roughness and decreased Hc and Hsw. Higher Tan changed the preferred orientations in the crystalline structures, leading to increased roughness and higher Hc and Hsw. This work shows that the Hc and Hsw of nanostructures can be reduced through engaging Conetic alloy in SyF stack. The Conetic-alloy-based SyF structures are a promising candidate as free layers in nanosized spintronic devices.

Field-anneal-induced magnetic anisotropy in highly textured Fe-Al magnetostrictive strips

Highly textured (011)[100] Goss-oriented rolled sheet Fe-Al alloy is a promising magnetostrictive material for use in bending mode sensors and vibrational energy harvesters. In this paper, we performed magnetic field annealing (FA) to induce magnetic anisotropy in strips of highly textured Fe-Al. Prior work suggests FA as a viable alternative to stress annealing (SA), which leads to buckling of Fe-Al rolled sheet samples. The Fe-Al strips studied here exhibited tetragonal magnetostriction values ((3/2)λsat = λ∥ − λ⟂) of ∼136 ppm along their length, which corresponds to ∼78% of the single crystal value along a <100> orientation. The effectiveness of FA on magnetic moment rotation was inferred by comparing post-FA magnetostriction measurements with the maximum possible yield, where λ∥= 0 and λ⟂= (3/2)λsat. Strain gauge data from the middle of the strip indicates that FA achieved ∼27% of the desired built-in uniaxial anisotropy along the parallel direction of the strip length, decreasing λ∥ by 25 ppm of the 95 ppm. Hall effect sensor data was used to assess the potential effect of FA on sensing and energy harvesting performance. FA improved the bending-stress-induced changes in magnetization near the clamped end of the strips by ∼45%. These results suggest that the FA was more effective in the region near the end of the strip than toward the middle of the strip, which we explain may be a result of the use of high temperature permanent magnets at the ends of the strips for the FA protocol.

Tunneling magnetoresistance sensors with different coupled free layers

Large differences of magnetic coercivity (HC), exchange coupling field (HE), and tunneling magnetoresistance ratio (TMR) in magnetic tunnel junctions with different coupled free layers are discussed. We demonstrate that the magnetization behavior of the free layer is not only dominated by the interfacial barrier layer but also affected largely by the magnetic or non-magnetic coupled free layers. All these parameters are sensitively controlled by the magnetic nanostructure, which can be tuned also by the magnetic annealing process. The optimized sensors exhibit a large field sensitivity of up to 261%/mT in the region of the reversal synthetic ferrimagnet at the pinned layers.

Enhanced soft magnetic properties of Fe-based amorphous powder cores by longitude magnetic field annealing

Abstract The longitude magnetic field annealing on the soft magnetic properties of Fe-based Fe 78 Si 9 B 13 amorphous powder cores were investigated. The magnetic properties of powder core greatly change when annealed under longitude magnetic field. With the increase of magnetic field intensity, the permeability of annealed powder core further increase. The core shows an enhanced effective magnetic permeability of 66 after longitude magnetic field annealing at an applied field of 30 Oe and temperature of 400 °C, which is attributed to the relief of internal stress and the variation of atomic structure. The permeability was improved by 8% and the frequency stability of FeSiB amorphous powder core is up to 2 MHz. The core loss decreases obviously and DC bias property stays at a same level compared with zero field treatment with the increase of magnetic field intensity. For the powder cores, the core loss ranges from 90 to 180 W/kg at 50 mT and 100 kHz, and DC bias property reaches over 70% at 100 Oe. This work provides a novel approach to improve permeability for Fe 78 Si 9 B 13 powder cores and also validates the application prospect of powder core in the work condition of different ripple currents, different loads and a wide frequency range (10 kHz–2 MHz).

Structure and Magnetic Property Changes of 2–2-Type BaTiO3–CoFe2O4 Composite Thin Films Induced by Magnetic Field Annealing

BaTiO3–CoFe2 O 4 composite thin films with different thicknesses were fabricated via chemical solution deposition. Magnetic annealing and non-field annealing processes were applied in the sintering process, respectively. Variations of the structure and magnetic properties of the composite films induced by the magnetic annealing were investigated. It is found that the mean grain size and grain boundary are increased and decreased, respectively. For the magnetic-annealed films, the internal strain is reduced with the increase of film thickness. Magnetic measurements show that the M s is also increased with the film thickness and the magnetic-annealed films have bigger M s values than the non-field-annealed films. Based on the experimental results, it can be concluded that the effect of magnetic annealing on the structure and properties of the composite films is decreased with the increase of film thickness.

A post-fabrication selective magnetic annealing technique in standard MEMS processes

A selective electrothermal magnetic annealing technique is introduced that provides programming capabilities for mechanical micro-resonators. In the proposed approach, the magnetic properties of resonators can be locally tuned in a post-fabrication batch-compatible process step. A prototype is implemented in a standard microfabrication process, where resonating ferromagnetic elements are suspended on top of a polysilicon resistive heater. The ferromagnetic elements consist of electroplated Nickel (Ni) with minor Iron (Fe) impurities. The electro-thermo-mechanical heating phenomenon is simulated for design purposes. The magnetization of micro-resonators with and without magnetic annealing is measured. The resulting magnetic property enhancement is illustrated by hysteresis (M-H) loop variations.

Decreased oxygen vacancies and improved ferroelectric properties of the BiFeO3 thin films with high magnetic field annealing

High magnetic field annealing (MFA) effects on polycrystalline BiFeO3 (BFO) thin films deposited on ITO buffered glass substrates by the chemical solution deposition (CSD) method have been investigated. Magnetic force induced by magnetic field leads to the increased crystallite size and the decrease in activation energy for boundary motion, especially for the low temperature annealed films. More Fe3+ ions are induced with increasing magnetic field to lower the free energy of the BFO films, which also leads to a decreased oxygen vacancy, resulting in low leakage current density. The increased remanent polarization and the decreased coercive field initially with the increase in magnetic field are attributed to the reduced domain wall pinning resulted from decreased oxygen vacancies and grain boundaries. Generally, the decreased coercivity and the improved ferroelectric polarization suggest high MFA is an effective way to enhance ferroelectric properties of the CSD-derived BiFeO3 thin films.

Fabrication, morphological, structural and magnetic properties of electrodeposited Fe3Pt nanowires and nanotubes

Highly ordered Fe3Pt nanowires (NWs) and nanotubes (NTs) embedded in anodic aluminum oxide (AAO) template have been fabricated by dc electrodeposition method. Response of heat treatment on structural and magnetic properties of the samples has been studied with and without the presence of magnetic field (1T). X-Ray Diffraction analysis shows chemically ordered L12 face centered cubic (FCC) as the dominant phase for Fe3Pt NWs and heat treatment improves crystallinity with retained its phase. Whereas, Fe3Pt NTs show amorphous behavior with and without magnetic field annealing. Furthermore, magnetic properties of the samples have been investigated by vibrating sample magnetometer (VSM). Magnetic parameters of Fe3Pt including magnetic coercivity, saturation magnetization, squareness and shape of MH-loops have been investigated as a result of simple and MF annealing.

Grain alignment due to magnetic-field annealing in MnBi:Bi nanocomposites

High-anisotropy arc-melted and field-annealed Mn100−xBix (x = 50–65) alloys have been investigated. Samples predominantly consist of low-temperature phase (LTP) MnBi and elemental Bi, where the LTP volume fraction and sample magnetization decrease with increasing x. All samples are hard ferromagnetic at room temperature and demonstrate a structural and magnetic phase transition at 630 K. For Mn35Bi65, the highest values for coercivity (4.6 kOe), magnetization remanence ratio (0.97), and energy product (4.9 MGOe) are measured at 540 K, near the melting point of bismuth. We explain the trend in magnetic properties as a consequence of c-axis alignment of MnBi grains facilitated by the molten Bi during magnetic field annealing.

Improved soft magnetic properties in nanocrystalline FeCuNbSiB Nanophy® cores by intense magnetic field annealing

The effect of high external magnetic field (up to 7T) on soft magnetic properties in nanocrystalline Fe74.1Si15.7Nb3.1B6.1Cu1 Nanophy® cores has been investigated. The as-quenched amorphous ribbons were nanocrystallized by annealing between 540 and 620°C in transverse magnetic field. By varying annealing field from 0 to 7T, induced anisotropy ranging from as low as 4J/m3 to as high as 41J/m3 is obtained. It is responsible for an increase in the cut-off frequency up to 300kHz when the material is submitted to dynamic magnetic excitations. A minimum coercivity of 0.74A/m is observed in the core annealed in 1T associated to low losses. The relative permeability decreases on increasing the annealing field intensity with a minimum value of 13,654 at 7T. Such permeability level opens the way to new applications of the Nanophy® alloys.

Effects of high magnetic field annealing on microstructure and multiferroic properties of Bi1−xLaxFeO3 ceramics

Effects of high magnetic field annealing on microstructure and multiferroic properties of Bi1−xLaxFeO3 have been investigated. It is found that the grain size of these materials prepared by annealing under a magnetic field becomes small and uniform. The magnetic coercive field of the samples synthesized under a magnetic field is higher than that of the samples prepared in the absence of magnetic field. It is also found that application of a magnetic field during annealing process can suppress the leakage behavior in Bi1−xLaxFeO3. As a result, ferroelectric properties are significantly improved by magnetic field annealing and the Bi0.85La0.15FeO3 specimens heated at 5T had the best remnant polarization value (2Pr) of 46.8μC/cm2, around 8 times higher than that of the samples fabricated at 0T.

(Invited) New Design of Double MgO-Based p-Mtj Spin-Valves with Top Co2Fe6B2 Free Layer Performain Highly Increased TMR Ratio and Thermal Stability

Perpendicular spin-transfer-torque magnetic-random-access-memory (p-STT MRAM) has intensively been researched as a promising memory cell to overcome a physical scaling limit of less than 20 nm in current dynamic-random-access-memory (DRAM) because of its fast write time (~10 ns), non-volatile memory operation, and extremely low power consumption. For realizing terra-bit-level integration of p-STT-MRAM cells fabricated with a selective transistor and a perpendicular-magnetic-tunnel-junction (p-MTJ) spin-valve, the p-MTJ spin-valves with a bottom CoFeB free layer using a Ta bridging and capping layer have been generally and widely researched. They need to achieve a high tunneling-magneto-resistance (TMR) ratio (>150%), thermal stability (Δ) (>74), and switching current (Jc) (~1x102 MA/cm2) at the back end of line (BEOL) temperature of 400oC. It has been reported that a Ta bridging and capping layer would be a good absorption layer for Boron (B) to enhance i-PMA characteristic but Ta atoms easily diffuse into the MgO tunneling barrier during ex- situ annealing temperature (or a thermal budget at BEOL)1,2. Thus, the p-MTJ spin-valves with a bottom CoFeB free layer using a tantalum (Ta: body-centered-cubic structure) bridging and capping layer have extreme difficulty achieving the TMR ratio of > 100% at the BEOL of 400 oC since the TMR ratio decreases rapidly as ex- situ annealing temperature (or a BEOL temperature) increases. Recently, the p-MTJ spin-valves with a top CoFeB free layer using a Ta bridging and capping layer have been intensively studied to obtain a higher TMR ratio at a higher ex- situ annealing temperature (or a BEOL temperature) since it would minimize the diffusion of platinum (Pt) atoms into the MgO tunneling barrier3-5. However, they confront a significant diffusion of Ta atoms into the MgO tunneling barrier at ex- situ annealing (or BEOL) of 400oC, so the b.c.c crystallinity of the MgO tunneling barrier is abruptly degraded, thereby rapidly decreasing the TMR ratio of the p-MTJ spin-valves. An innovative solution proposed in this paper is a new design of a p-MTJ spin-valve with a top Co2Fe6B2 free layer using a W bridging with sub-nanoscale thickness (~0.24 nm) and a tungsten (W: body-centered-cubic structure) capping layer with nanoscale thickness (~4.0 nm). The proposed design demonstrated no diffusion of Ta atoms into the MgO tunneling barrier and minimized the diffusion of Fe atoms at both Co2Fe6B2 free and pinned layer at an ex-situ annealing of 400oC. Therefore, b.c.c crystallinity degradation of the MgO tunneling barrier could be prevented, and high PMA magnetic moments at both Co2Fe6B2 free and pinned layers could be achieved. Thus, the p-MTJ spin-valve with a Co2Fe6B2 free layer using a W bridging and capping layer with nanoscale thickness (~4.0 nm) achieved the TMR ratio of ~143% at ex- situ annealing of 400oC, as shown Fig. 1. Furthermore, as a way to achieve a TMR ratio of >150% at 400°C, in this paper, we present the design of a new double MgO-based p-MTJ spin-valve with a top Co2Fe6B2 free layer by inserting a nanoscale Fe diffusion barrier (~0.30 nm: only two Fe atomic layers thick) between the W capping layer (~ 4.0 nm in thickness) and MgO capping layer (~1.0 nm in thickness). This new p-MTJ spin-valve had a TMR ratio of ~154% and Δ of 90 in ex-situ magnetic annealing at 400°C, as shown Fig. 2. * This work was supported by a Basic Science Research Program grant from the National Research Foundation of Korea (NRF) funded by the Korean government (MSIP) (No. 2014R1A2A1A01006474) and the Brain Korea 21 PLUS Program in 2014. Reference [1] J. Appl. Phys. 2009, 106, 023920 [2] Acta Materialia 2015, 87, 259 [3] IEDM 2015, pp. 26. 2 [4] IEDM 2015, pp. 26. 3 [5] IEDM 2015, pp. 26. 4 Fig. 1. (a) p-MTJ spin-valve structure using a Ta bridging and capping layer, (b) p-MTJ spin-valve structure using a W bridging and capping layer, and (c) dependency of the TMR ratio on bridging and capping layer thickness for both p-MTJ spin-valves using Ta and W bridging and capping layers. Fig. 2. Dependence of TMR ratio on nanoscale thickness of Fe diffusion barrier for double MgO-based p-MTJ spin-valves with a top Co2Fe6B2 free layer. Figure 1

Interdiffusion and magnetic properties of Co/Cu/Co trilayers produced by high magnetic field annealing

The influence of interdiffusion on the magnetic properties of Co/Cu/Co trilayers after annealing in the presence of a strong magnetic field was investigated. The interdiffusion zone of films that were annealed at temperatures of 573 K and 773 K in the presence of high magnetic fields were not affected. However, the interdiffusion zone of films annealed at 673 K in the presence of a high magnetic field increased significantly due to phase transformation. Meanwhile, the high magnetic field has an influence on alloying process by affects the concentration distribution of Co and Cu across the interface because of magnetic force. The change in the interdiffusion, caused by high magnetic field annealing, decreased the content of the magnetic phase. This decreasing in the magnetic phase reduced the saturation magnetization. The coercivity decreases in the sample annealed at 673 K with a high magnetic field can result from not completely alloying compared with non-field case.

Processing of alnico permanent magnets by advanced directional solidification methods

Advanced directional solidification methods have been used to produce large (>15cm length) castings of Alnico permanent magnets with highly oriented columnar microstructures. In combination with subsequent thermomagnetic and draw thermal treatment, this method was used to enable the high coercivity, high-Titanium Alnico composition of 39% Co, 29.5% Fe, 14% Ni, 7.5% Ti, 7% Al, 3% Cu (wt%) to have an intrinsic coercivity (Hci) of 2.0kOe, a remanence (Br) of 10.2kG, and an energy product (BH)max of 10.9MGOe. These properties compare favorably to typical properties for the commercial Alnico 9. Directional solidification of higher Ti compositions yielded anisotropic columnar grained microstructures if high heat extraction rates through the mold surface of at least 200kW/m2 were attained. This was achieved through the use of a thin walled (5mm thick) high thermal conductivity SiC shell mold extracted from a molten Sn bath at a withdrawal rate of at least 200mm/h. However, higher Ti compositions did not result in further increases in magnet performance. Images of the microstructures collected by scanning electron microscopy (SEM) reveal a majority α phase with inclusions of secondary αγ phase. Transmission electron microscopy (TEM) reveals that the α phase has a spinodally decomposed microstructure of FeCo-rich needles in a NiAl-rich matrix. In the 7.5% Ti composition the diameter distribution of the FeCo needles was bimodal with the majority having diameters of approximately 50nm with a small fraction having diameters of approximately 10nm. The needles formed a mosaic pattern and were elongated along one 〈001〉 crystal direction (parallel to the field used during magnetic annealing). Cu precipitates were observed between the needles. Regions of abnormal spinodal morphology appeared to correlate with secondary phase precipitates. The presence of these abnormalities did not prevent the material from displaying superior magnetic properties in the 7.5% Ti composition. Higher Ti compositions did not display the preferred spinodal microstructure, explaining their inferior magnetic properties.

Linearization of Magnetic Sensors With a Weakly Pinned Free-Layer MTJ Stack Using a Three-Step Annealing Process

In this paper, a three-step magnetic annealing process is used to linearize magnetic tunnel junctions (MTJs) with two exchange pinning layers: one used to strongly pin the reference synthetic antiferromagnet (SAF) and the other one used to weakly pin the magnetic sensing layer. With respect to a more conventional two-step annealing process, the advantage of the three annealing cycle is to provide independent control over the three relevant internal fields, which apart from the demagnetizing field, control the linear response of large area/low aspect ratio MTJs: the sensing layer soft pinning field (SL– $H_{\mathrm{ ex}})$ , the sensing layer uniaxial anisotropy field (SL– $H_{k})$ , and the reference layer strong pinning field (RL– $H_{\mathrm{ ex}})$ . As a result of the three annealing process, a configuration, where SL– $H_{k}$ and SL– $H_{\mathrm{ ex}}$ point both in a direction orthogonal to RL– $H_{\mathrm{ ex}}$ , can be achieved resulting in very good linearity and low coercivity without compromising the sensitivity of the devices, as desired for applications, such as magnetocardiography that targets the detection of magnetic fields in the pT/Hz0.5 range at room temperature and low frequencies within the 1/ $f$ noise.

Phase Relationship and Magnetostriction of Tb–Dy–Ho–Fe Alloys

The phase relationship of $\mbox{Tb}_{0.26}\mbox{Dy}_{0.49}\mbox{Ho}_{0.25}\mbox{Fe}_{x}$ $(1.6\le x\le 2.4)$ alloys in the Tb–Dy–Ho–Fe system was determined by using optical microscopy, X-ray diffraction, and differential thermal analysis. The vertical section of $\mbox{Tb}_{{\kern-.5pt}0{\kern-.25pt}.{\kern-.25pt}26}\mbox{Dy}_{{\kern-.25pt}0{\kern-.25pt}.{\kern-.25pt}49}\mbox{Ho}_{{\kern-.5pt}0{\kern-.25pt}.{\kern-.25pt}25}\mbox{Fe}_{{\kern-.5pt}x}$ alloys consists of two single-phase regions, namely, L (liquid) and (Tb, Dy, Ho)Fe 2, and four two-phase regions, namely, L + (Tb, Dy, Ho)Fe 3, L + (Tb, Dy, Ho)Fe 2, (Tb, Dy, Ho)Fe 2 + (Tb, Dy, Ho)Fe 3, and (Tb, Dy, Ho)Fe 2 + (Tb, Dy, Ho). The range between the liquidus and peritectic temperatures for $\mbox{Tb}_{0.26}\mbox{Dy}_{0.49}\mbox{Ho}_{0.25}\mbox{Fe}_{x}$ alloys becomes narrow with addition of Ho, which is beneficial to decrease the properitectic (Tb, Dy, Ho)Fe 3 phase. The magnetic field dependence of magnetostriction $(\lambda_{//},\lambda_{\perp})$ for $\mbox{Tb}_{0.26}\mbox{Dy}_{0.49}\mbox{Ho}_{0.25}\mbox{Fe}_{x}$ alloys has been determined. The magnetostriction quickly increases with increasing magnetic field value when it is less than 240 kA/m. Among the present studied alloys, the sample with $x=1.9$ possesses the largest magnetostriction. It has been found that magnetic annealing improves the magnetostriction $\lambda_{//}$ of Tb 0.26Dy 0.49Ho 0.25Fe 1.9 alloy.

Tuning microstructure and magnetic properties of electrodeposited CoNiP films by high magnetic field annealing

A high magnetic field (up to 12T) has been used to anneal 2.6-µm-thick Co50Ni40P10 films formed by pulse electrodeposition. The effects of high magnetic field annealing on the microstructure and magnetic properties of CoNiP thin films have been investigated. It was found that a high magnetic field accelerated a phase transformation from fcc to hcp and enhanced the preferred hcp-(002) orientation during annealing. Compared with the films annealed without a magnetic field, annealing at 12T decreased the surface particle size, roughness, and coercivity, but increased the saturation magnetization and remanent magnetization of CoNiP films. The out-of-plane coercivity was higher than that the in-plane for the as-deposited films. After annealing without a magnetic field, the out-of-plane coercivity was equal to that of the in-plane. However, the out-of-plane coercivity was higher than that of the in-plane when annealing at 12T. These results indicate that high magnetic field annealing is an effective method for tuning the microstructure and magnetic properties of thin films.

Structure and texture in Ni–30% Co alloy ribbons subjected to annealing in high magnetic field

The structure and texture in the Ni–30% Co alloy subjected to cold rolling and annealings in strong dc magnetic field at the temperatures of above and below the Curie point are studied. It has been shown that, at all annealing temperatures, the average grain size after magnetic annealing is smaller than after annealing without filed. After the magnetic annealing of the alloy in the ferromagnetic state, the volume fraction of grains with cube orientation decreases and the volume fraction of the components of deformationinduced texture increases.