Amorphous Magnetic Alloys Research Articles

Structural relaxation of amorphous metallic alloys

Abstract The structural factor and a total pair correlation function for amorphous magnetic metal alloys of Fe60.8Co20.2B14Si5 and Fe76.8Ni1.2B13.2Si8.8 is obtained using neutron diffraction method. It is shown that the cryogenic sample processing (during some hours of conditioning at the liquid nitrogen temperature) affects the short-range order (up to ∼1.2 nm ). The short order change is explained in frame of the structural relaxation. It was found that there exists a correlation between the short-range order and magnetic properties.

アモルファスおよび多結晶金属系軟磁性材料の開発

Recently, soft magnetic alloys are used for many kinds of applications such as power electrical equipments and electronic appliances. Several ten years ago, only polycrystalline soft magnetic alloys were used for industrial usage. However, around 30 years ago, amorphous soft magnetic alloys produced by the rapid quenching technique were invented and have been developed. Around 15 years ago, nano-crystalline soft magnetic alloys were invented by the authors. This paper reports Fe-Si-Al alloys for the magnetic recording heads, Co-based amorphous alloys for switched mode power supplies, and nano-crystalline soft magnetic alloys with particular emphasis.

A study on the resistance minima in an amorphous alloy at low temperature

In this paper, we study the electrical resistance of nonmagnetic amorphous alloy Cu60Zr20Hf10Ti10 and amorphous ferromagnet Fe61Co7Zr10Mo5W2B15. We fit the c urve in the light of special models, and analyze the origination of the minima which occurs in both of the samples. The contributions both from the disorder structure and magnetic status are discussed.

Stability and crystallization of Fe–Co–Nb–B amorphous alloys

New soft magnetic amorphous alloys with a wide supercooled liquid region were obtained by increasing the boron content (up to 30 at.%) and by addition of cobalt (composition range between 5 and 42 at.%) in FeNbB based materials. Upon thermal treatments, the stability and the crystallization behavior of Fe 52Co 10Nb 8B 30 and Fe 22Co 40Nb 8B 30 have been studied by using X-ray diffraction (XRD) and transmission electron microscopy (TEM). On the other hand, the Curie temperature change, T c, of the remaining amorphous phases has been determined by thermomagnetic analysis (TMG). Sub-micrometric fcc-(Co,Fe) and fcc-(Fe,Co) 21Nb 2B 6 grains were observed to crystallize at a relatively high temperature (950–970 K) providing an excellent stability of the amorphous states. Due to the partitioning behavior, occurring during crystallization, the Curie temperature of the remaining amorphous structure is observed to increase in the case of the Fe 52Co 10Nb 8B 30 composition while a decrease of T c to the lower temperatures is observed with the Fe 22Co 40Nb 8B 30 composition.

Phase transformation in iron/cobalt-based amorphous alloys revealed by thermal and magnetic techniques

The crystallization kinetics and the changes in the structure and magnetic properties of some iron/cobalt-based amorphous alloys have been investigated by means of differential scanning calorimetry (DSC), X-ray diffraction (XRD) and 57 Fe transmission Mössbauer spectroscopy. Heating and isothermal treatments were used to induce mainly nucleation and growth of α-Fe/Co and Fe 2B in a-Fe 67Co 18B 14Si 1 alloy and Fe 2B and FeNi 3 phases in a-Fe 4Co 65B 15Si 14Ni 2 alloy. The crystallization kinetics of the α-Fe/Co phase was studied in the theoretical frame of the Johnson–Mehl–Avrami model. The 57 Fe Mössbauer spectra of the as-received alloys show the expected broad sextet typical of amorphous magnetic alloys. The isothermal treatments conducted at temperatures below the first exothermic peak in the DSC curve of the a-Fe 67Co 18B 14Si 1 alloy (at about 690 K) lead to the crystallization of only the α-Fe/Co phase, as observed by XRD and Mössbauer results. For temperatures just below the second crystallization peak (at about 785 K in the DSC curve), assigned as the Fe 2B formation temperature, the Mössbauer spectra show two sextets associated with the Fe 2B and α-Fe/Co phases. For the a-Fe 4Co 65B 15Si 14Ni 2 alloy, no crystallization is observed by XRD for samples heat-treated at temperatures up to 761 K during 48 h. However, XRD and Mössbauer results in the sample heat-treated for 12 h at 1123 K clearly indicate the presence of FeNi 3 and Fe 2B phases.

Design and preparation of new soft magnetic bulk amorphous alloys for applications

This work is focussed on our recent results on the preparation and frequency dependence (5 Hz-10 MHz) characterisation of new bulk amorphous alloys with large supercooled liquid region and good soft magnetic properties in (Fe,Co,Ni) 70 M 10 B 20 (M = Zr, Nb, Ti, Ta) multicomponent systems. Melt-spinning, suction casting and Cu-mould casting methods were used to prepare 2-6 mm wide and 20-200 μm thick amorphous ribbons, as well as rods and ring-shaped samples with diameters and heights no larger than 3 mm, respectively. Electrical resistivity ((180-230) x 10 -8 Ω m) and magnetic properties such as coercive field (H c < 6A/m), magnetic permeability (up to 3 x 10 4 , depending on composition), saturation magnetisation (μ 0 M s ∼ 1.2 T), Curie temperature (T C about 600 K) and core losses were determined. The influence of the preparation conditions, composition and thermal or thermomagnetic treatments on the magnetic properties and electrical resistivity in the as-cast state is discussed in detail. The results are used to design new applications of bulk amorphous alloys with soft magnetic properties.

The thermal, magnetic, and structural characterization of the crystallization kinetics of Fe/sub 88/Zr/sub 7/B/sub 4/Cu/sub 1/, an amorphous soft magnetic ribbon

The characterization of the crystallization kinetics of an amorphous soft magnetic alloy, Fe/sub 88/Zr/sub 7/B/sub 4/Cu/sub 1/, called NANOPERM, is presented. Vibrating sample magnetometry (VSM), X-ray diffractometry, and differential scanning calorimetry have been used to observe crystallization kinetics. The VSM observations take advantage of the Curie temperature of the amorphous phase Tc-/sub amorphous/ of the NANOPERM alloy being below its primary crystallization temperature T/sub x1/. This allows for the volume of nanocrystals transformed in the crystallization process to be inferred magnetically, as well as thermally and structurally. The Johnson-Mehl-Avrami model for isothermal crystallization kinetics is compared with the Kissinger model for nonisothermal crystallization kinetics using data gathered from the three characterization methods. Linear regression and nonlinear regression analysis of crystallization data for NANOPERM ribbon and the significance of the values that describe them, namely, the activation energy Q and the morphology index n are investigated for isothermal and constant-heating crystallization. The activation energy for NANOPERM ribbon is presented here to be in the range of Q=2.8-3.4 eV, with the crystallization kinetics proceeding by three-dimensional diffusion and immediate nucleation, where the morphology index is n=1.5. A time constant to account for initial nonisothermal conditions during isothermal heating is introduced and determined to be T=120-200 s.

고 비정질 형성능을 가진 FeBSiNb 합금 리본의 자기적 특성

벌크 비정질 형성능과 큰 포화자속밀도를 가지는 FeBSiNb계 아몰퍼스 합금 리본을 22~102<TEX>$\mu\textrm{m}$</TEX>의 두께 범위에서 단롤형 액체 급냉법으로 제조하였다. 이 합금은 두께 증가에 따라 보자력이 감소하고 최대투자율 및 교류투자율이 증가하였으며, 자기이력곡선의 각형비가 감소하였다. 한편 전기 비저항은 두께와 상관없이 거의 일정한 값을 나타내었다. 또 지구 관찰 결과, 두께가 증가하면 내부 자기 이방성의 변화에 따라 자구가 미세화 되고 보다 복잡한 자구 구조를 갖는 것으로 나타났다. 두께 81<TEX>$\mu\textrm{m}$</TEX>인 합금의 경우, 24 mOe의 작은 보자력과 1KHz에서 12,000이상의 높은 실효투자율을 나타내어 일반적인 고 연자성 비정질 합금(두께 약 20<TEX>$\mu\textrm{m}$</TEX>)의 특성을 능가하였다. 이와 같은 두꺼운 FeBSiNb 비정질 합금의 우수한 연자성은 자벽이동에 대한 표면 고착 효과의 감소 및 수직자기이방성 성분의 출현과 미세화 된 자구 구조에 그 원인이 있는 것으로 평가되었다. Amorphous FeBSiNb alloy ribbons having bulk glass forming ability and high saturation magnetic flux density were produced by single-roller melt spinning apparatus in the thickness range of 22∼102㎛. With the increase of thickness, the coercive force and squareness ratio decreased, while maximum permeability and AC permeability increased. However electrical resistivity was almost constant. Furthermore refined and complex magnetic domain structure was observed in thicker ribbons owing to the change in internal magnetic anisotropy. For the alloy with the thickness of 81㎛, small coercive force of 24 mOe and high effective permeability of 12,000 at 1㎑ were obtained, those are considered to be better comparing to the conventional soft magnetic amorphous alloys (∼20 ㎛). The good soft magnetic properties of the thick FeBSiNb amorphous alloys were attributed to the decrease in surface pinning effect during wall motion, appearance of perpendicular anisotropy and resulted domain refinement.

Structural Relaxation and Crystallisation in Fe-Cr-Si-B and Fe-Cu-Cr-Si-B Amorphous Alloys

Structural relaxation, crystallisation and optimisation processes in soft magnetic amorphous alloys based on iron are examined by applying different experimental techniques: X-ray diffraction analysis, high-resolution electron microscopy, measurements of magnetic and electric properties (permeability, after-effect, resistivity). The presented results are discussed in terms of annealing out of microvoids, formation of a nanocrystalline phase and changes of effective magnetostriction constant.

Defect study of crystallized amorphous Co-rich magnetic alloy

Microstructure of Co-rich amorphous magnetic alloy, Co 74.26Fe 4.74B 18.9Si 2.1, formed by planar casting process was characterized using transmission electron microscopy (TEM) and auger electron spectroscopy (AES) to determine the cause of deterioration of the magnetic properties during extended manufacturing trial of the strip as domain wall pinned sensors. TEM analysis showed that micro-crystalline SiC particle contamination has caused the metastable B 4Si crystallites to nucleate at the wheel (cold) side of the as-cast film. The B 4Si crystals depleted the metalloids at the interface, which in turn, resulted in premature precipitation and excessive growth of Co grains at the perimeter of B 4Si particles. Such microstructural inhomogeneity remained on the wheel side of the film even after field-annealing, which adversely affected the domain pinning. AES depth analysis also indicated that the as-cast film had a steep concentration gradient with the wheel side, being depleted of B and Si. The gradient flattened slightly during annealing. As the microstructural and compositional inhomogeneities disrupt the layered structure essential for the magnetic sensor, it is critical to control the processing parameters to eliminate the sources of such defects discussed above.

Investigation of amorphous magnetic alloys by X-ray absorption spectroscopy

Investigation of amorphous magnetic alloys by X-ray absorption spectroscopy

Applications of amorphous magnetic alloys in electronic devices

Some of the features of amorphous magnetic alloys that differentiate them from other soft magnetic materials include: low magnetic loss, fast flux reversal, high electrical resistivity and low acoustic loss. Furthermore, a wide range of B– H characteristics can be obtained through alloy design and heat-treatment of the alloys under different conditions. The versatile properties thus obtained can then be utilized in a number of magnetic applications ranging from large electrical power devices such as transformers and motors to recording heads and to anti-pilferage markers. This paper reviews the applications of various amorphous magnetic alloys in electronic devices including magnetic components in power electronics, telecommunication equipment, automotive parts and sensing devices. Relationships between property requirements and material capabilities are also discussed.

Magnetoelastic thin films for high-frequency applications

High-frequency magnetic thin films with cut-off frequencies well above 2 GHz and good magnetoelastic properties are key materials for the development of new magnetic devices such as remote-interrogated magnetoelastic sensors or micro-inductors. In order to achieve high cut-off frequencies the films must have high magnetization, high anisotropy field, moderate permeability and resistivity. Therefore, multilayered thin films consisting of the transition metal alloy Fe/sub 60/Co/sub 60/ and the amorphous soft magnetic alloy Co/sub 80/B/sub 20/ have been developed which show cut-off frequencies higher than 2 GHz combined with good magnetoelastic properties.

On the Nature of the Hysteresis Loop Shift in Amorphous Soft Magnetic Alloys

The influence of annealing temperature, rate of cooling, magnetic field frequency under thermomagnetic treatment on the hysteresis loop shift field value of Fe5Co70Si15B10 and Fe60Co20Si5B15 amorphous alloys samples has been studied. The relation of the structural state of amorphous alloys with the shift field value of the hysteresis loop has been studied. The physical explanation of this effect is proposed on the basis of obtained data.

Oxidation of Amorphous Co75.26−xFe4.74(BSi)20+x Magnetic Alloy

The oxidation characteristics of the Co-rich amorphous magnetic alloy, $${\text{Co}}_{75.26 - x} {\text{Fe}}_{{\text{4}}{\text{.74}}} \left( {{\text{BSi}}} \right)_{20 + x}$$ were investigated. A TEM study of the microstructure revealed a complex oxidation behavior of the alloy depending on composition, especially the boron and silicon concentrations. It was determined that the critical concentration of the metalloid to be 21 at.% above, which a continuous layer of an amorphous borosilicate phase formed on the surface. Phase separation of the surface oxide was also observed when the composition is rich in boron. The metalloid (boron and silicon) concentration was critical in determining the surface-oxide morphology, which in turn, affected the subsurface microstructure. As the magnetization behavior of the Co-rich amorphous alloy depends upon the surface oxide and the internal-oxide precipitates, the guidelines are provided by which one can engineer the microstructure of the alloy to optimize the magnetic properties.

Changes of chemical composition and structure of soft magnetic nanocrystalline Fe–Zr–N alloy under vacuum annealing

The amorphous soft magnetic alloys were produced by magnetron sputtering of Fe–8 at%Zr target in Ar and Ar+10%N 2 atmospheres as films 1.5–2.5 μm thick. X-ray diffraction analysis showed that annealing of the films resulted in formation of BCC Fe-based phase and additionally Fe 2Zr in the Fe–Zr films. Amorphous phase in the Fe–Zr–N films is more thermostable in comparison with that in the Fe–Zr ones. X-ray spectrum microanalysis showed that nitrogen content in the Fe–Zr–N films decreases significantly during vacuum annealing.

Present status of amorphous soft magnetic alloys

Application of amorphous soft magnets in electric-utility and industrial transformers are increasingly being adopted, helping to solve global warming and energy-saving problems. In addition, amorphous metal-based magnetic components are used in power electronics, telecommunication equipment, sensing devices, electronic article surveillance systems, etc. Some magnetic inductors find applications in pulse power devices, automotive ignition coils, and electric power conditioning systems. All of these applications are possible because of faster flux reversal, lower magnetic loss and more versatile property modification achievable in amorphous alloys. Improvements in materials processing and device fabrication technology will continue to take place, which will further increase the universe of application of amorphous soft magnets. Some fundamental problems associated with the applications are mentioned.

Element specific spin-resolved densities of states in amorphous Fe75B25 probed with a synchrotron radiation source

The partial spin-dependent densities of states (DOS) of both the iron and the boron in Fe–B amorphous magnetic alloys have been determined from spin-resolved photoemission using a synchrotron radiation source. The spin-integrated energy distribution curves (EDCs), polarization spectra and the spin-resolved EDCs show distinct differences between 15 and 40 eV photon energies due to strikingly different photon energy dependencies of the cross sections of Fe-d and B-p states. The B-p states were found to hybridize with Fe-d states and occupy a binding energy range of about 1–5.5 eV with a negative polarization; i.e., the B moment is “antiferromagetically” coupled with that of the Fe-d moment.

Bulk Amorphous Fe&amp;ndash;Ga&amp;ndash;P&amp;ndash;B&amp;ndash;C Alloys with a Large Supercooled Liquid Region

Amorphous Fe 75 Ga 5 P 12 C 4 B 4 alloy rods were prepared in the diameter range up to 1.0 mm by copper mold casting. The glass transition temperature (T g ), supercooled liquid region (ΔT x (= T x - T g )) and reduced glass transition temperature (T g /T m ) of the amorphous alloy rods are 731 K, 37K and 0.61, respectively, in agreement with the results for the corresponding melt-spun amorphous alloy ribbon. The Curie temperature (T c ), saturated magnetization (I s ), coercive force (H c ) and saturated magnetostriction (λ s ) of the melt-spun amorphous ribbon are 622 K, 1.28T, 1.6 A/m and 19.6 × 10 -6 , respectively, in which the T c and I s are nearly the same as those for the amorphous alloy rod with a diameter of 0.5 mm. The simultaneous achievement of high T g /T m , large ΔT x and good soft magnetic properties for the simple Fe-based alloy system is promising for the future development of bulk amorphous Fe-based soft magnetic alloys.

Preparation and Characterization of the Soft Magnetic FeCo-based Amorphous Alloy with Enhanced Magnetic Properties and Thermal Stability

AbstractA glassy structure was formed in the Fe40Co40P14B6 alloy by melt-spinning technique. The as-quenched 2-8 mm wide and 15-30 [.proportional]m thick ribbons exhibit good soft magnetic properties: the saturation magnetization of 1.45 T, the coercive force of 4 A/m and maximum differential permeability at 60 Hz of about 90000. The FeCo-based glass crystallizes via eutectic reaction into a mixture of an austenite and a b.c. tetragonal Fe3P-like phase similar to that of the well-known Fe40Ni40P14B6metallic glass, but at temperatures about 60 K higher than the latter. The evaluation of the thermodynamic and kinetic parameters of crystallization process brought us to the conclusion that the improved thermal stability of the Fe40Co40P14B6 glass is caused by the enhanced interfacial nucleus-glass energy.