High Effective Permeability Research Articles

Glass-forming ability and magnetic properties of CoFeMoYB bulk glassy alloys with large supercooled liquid region

Co-based bulk glassy alloys with diameters up to 4 mm were formed in Co 41+ x Fe 28Mo 4Y 5− x B 22 ( x = 0–1.5) system. The effect of Y content on the glass-forming ability and soft-magnetic properties of the Co-based bulk glassy alloys was investigated. With an increase of Y content from 3.5 to 5 at%, in addition to slight increases of glass transition temperature from 843 to 847 K and supercooled liquid region increases from 73 to 94 K, the addition of Y was found to be effective in approaching alloy to a eutectic point. Except for high glass-forming ability, the Co-based bulk glassy alloys exhibit good soft-magnetic properties, i.e., high saturation magnetization of 0.80–0.87 T, low coercive force of 2.87–3.34 A/m, high effective permeability at 1 kHz of 1.26–1.74 × 10 4 under a field of 1 A/m.

New Excellent Soft Magnetic FeSiBPCu Nanocrystallized Alloys With High $B_{s}$ of 1.9 T From Nanohetero-Amorphous Phase

The melt-spun Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">83.3-84.3</sub> Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sub> P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3-4</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.7</sub> (at%) alloys have heterogeneous amorphous structures including a large amount of alpha-Fe clusters with less than 3 nm in size after rapid solidification, due to the unusual effect of the simultaneous addition of the small amounts of P and Cu. A homogeneous nanocrystalline structure composed of alpha-Fe grains with a size of about less than 20 nm can be realized by crystallizing the heteroamorphous alloys. The Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">83.3-84.3</sub> Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sub> P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3-4</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.7</sub> nanocrystalline alloys show significantly high saturation magnetic flux density of 1.88-1.94 T almost comparable to the commercial silicon steel. The Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">83.3-84.3</sub> Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sub> P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3-4</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.7</sub> alloys exhibit excellent magnetic softness; low coercivity of 7-10 A/m, relatively high effective permeability of 16 000-25 000 at 1 kHz due to the simultaneous realization of the uniform nanostructure composed by fine alpha-Fe grains and a small magnetostriction of 2-3 times 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> . The nanocrystalline alloys also exhibit much smaller W than the silicon steel over the B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> range up to 1.7 T due to significantly higher B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> and excellent magnetic softness. Therefore, the Fe-Si-B-P-Cu alloys have a great advantage for engineering and industry, and, thus, should make a contribution to energy saving and conservation of earth's resources and environment.

Microwave Properties of Sandwich Structure Based on Iron and Barium Nanoparticles

The high frequency intrinsic and effective permeability was calculated for spherical iron and barium particles in a nonmagnetic matrix (epoxy resin) by using the combination of Landau-Lifshitz-Gilbert equation and extended Bruggeman’s effective medium theory with the consideration of the skin effect. It was found that the microwave properties of the composite were influenced by many parameters, such as damping parameter, volume fractions and size of magnetic components. The sandwich microwave absorber with reflection loss &lt; −10 dB over the range of 6-22 GHz was achieved. The thickness of absorber is only 4.25 mm.

Synthesis of ferromagnetic Fe-based bulk glassy alloys in the Fe–Si–B–P–C system

Multi-component Fe76P5(BxSiyCz)19 glassy alloys were fount to exhibit a distinct glass transition, followed by a supercooled liquid region before crystallization in a rather wide composition range. The largest value of the supercooled liquid region defined by the difference between the glass transition temperature (Tg) and crystallization temperature (Tx), ΔTx (=Tx − Tg) was 54 K for Fe76P5(Si0.3B0.5C0.2)19. Furthermore, the crystallization of the glassy alloy occurs through a single exothermic reaction, which means simultaneous precipitation of several kinds of crystallites leading to higher glassy forming ability (GFA) due to the necessity of the atomic rearrangement on a long range scale. By copper mold casting, bulk glassy alloy rods with diameters up to 3 mm were produced. The representative Fe76P5(B0.5Si0.3C0.2)19 alloy exhibits rather high saturation magnetization of 1.44 T with good soft-magnetic properties, i.e., low coercive force of 1.2 A/m, and high effective permeability of 17,600 at 1 kHz under a field of 1 A/m. The bulk glassy alloy also possesses superhigh fracture strength of 3700 MPa and Young's modulus of 185 GPa. This new ferromagnetic bulk glassy alloy simultaneously exhibiting high GFA, rather high saturation magnetization, excellent soft-magnetic properties and superhigh fracture strength is promising for future applications as not only functional but also structural material.

Enhanced soft-magnetic and corrosion properties of Fe-based bulk glassy alloys with improved plasticity through the addition of Cr

Abstract The influence of Cr addition on glass-forming ability (GFA), corrosion resistance, and magnetic and mechanical properties of the Fe–Co–B–Si–Nb bulk glassy alloy (BGA) has been investigated. Except for a slight decrease in its GFA, the Cr addition caused an increase of corrosion resistance as well as an improvement of soft-magnetic properties and mechanical behaviors for this alloy within the composition range studied. BGA rods with diameters up to 4 mm were produced by copper mold casting technique. These glassy alloys exhibit a rather high saturation magnetization of 0.811–1.040 T, low coercive force of 0.6–1.7 A/m, high effective permeability of (2.37–3.41) × 10 4 at 1 kHz under a field of 1 A/m, and extremely low saturation magnetostriction of (0.43–4.17) × 10 −6 . These BGAs also possess ultrahigh fracture strength of 4010–4274 MPa, Young's modulus of 200–215 GPa, elastic strain of about 2% and plastic strain reaching 0.7%. Moreover, the corrosion rate and corrosion current density of the glassy alloy rods in simulated industrial environments contaminated with SO 2 decreased significantly from 3.47 × 10 −2 to 9.2 × 10 −3 mm/year and 1.5 × 10 −5 to 6.7 × 10 −7 A/cm 2 , respectively, with increasing Cr content from 0 to 4 at.%, illustrating that the addition of Cr is effective in increasing the corrosion resistance. Furthermore, the mechanisms for the high GFA, distinct plasticity strain, good corrosion resistance, and excellent soft-magnetic properties of the Fe-based BGAs are discussed.

Formation, Mechanical and Magnetic Properties of (Fe,Co)-B-Si-Nb Bulk Glassy Alloys

Fe- and Co-based bulk glassy alloys (BGAs) with diameters up to 5 and 4 mm were formed respectively in (Fe,Co)-B-Si-Nb system by copper mold casting. The Fe-based glassy alloys in [(Fe1-xCox)0.75B0.2Si0.05]96Nb4 system exhibit saturation magnetization (Is) of 0.84-1.13 T and low coercive force (Hc) of 1.5-2.7 A/m. Its BGAs exhibit superhigh strength ( σ f) of 3900-4250 MPa, Young’s modulus (E) of 190-210 GPa, elastic strain (εe) of 0.02 and plastic strain (εp) of 0.0025. For the Co-based glassy alloys in [(Co1-xFex)0.75B0.2Si0.05]96Nb4 system, in addition to superhigh σ f of 3980-4170 MPa, they also exhibit excellent soft magnetic properties, i.e., Is of 0.71-0.97 T, Hc of 0.7-1.8 A/m, high effective permeability (μe) of 1.48-3.25×104 at 1 kHz under a field of 1 A/m, and extremely low saturation magnetostriction (λs) of 0.55-5.76×10-6.

FeMoGaPCBSi バルクガラス合金の作製と軟磁気特性

The addition of 2 at%Mo combined with 2 at%Si was found to be effective for the extension of the supercooled liquid region (ΔTx) and approaching alloy to a eutectic point in the Fe77-xMoxGa3P10C4B4Si2 alloy system. The ΔTx value is 33 K for the Fe77Ga3P12C4B4 glassy alloy, and increases to 60 K for the Fe75Mo2Ga3P10C4B4Si2 glassy alloy. Besides, this glassy alloy exhibits a high reduced glass transition temperature (Tg/Tl) of 0.6. The large ΔTx and high Tg/Tl enabled us to prepare the Fe75Mo2Ga3P10C4B4Si2 bulk glassy alloy successfully with a diameter of 2 mm and high saturation magnetization (Is) of 1.27 T. The Fe75Mo2Ga3P10C4B4Si2 glassy alloy also exhibits good soft magnetic properties, i.e., high effective permeability at 1 kHz of 1.1×104 and low coercive force of 5 A/m.

Flow channeling in a single fracture induced by shear displacement

The effect on the transport properties of a fracture of a shear displacement u → between its complementary surfaces is investigated experimentally and numerically. The shear displacement u → induces an anisotropy of the fracture aperture field with a correlation length scaling of | u → | , which is significantly larger in the direction perpendicular to u → . This reflects the presence of long fluid flow channels perpendicular to the shear displacement, resulting in a higher effective permeability in that direction. Such channels will have a strong influence on the transport characteristics of a fracture, such as, for instance, its thermal exchange area, crucial for geothermal applications. Miscible displacement fronts in shear-displaced fractures obtained experimentally display a self-affine geometry with a characteristic exponent directly related to that of the fracture surfaces. We present a simple model, based on the channeling of the aperture field, which reproduces the front geometry when the mean flow is parallel to the channels created by the shear displacement.

Effect of Cr addition on the glass-forming ability, magnetic properties, and corrosion resistance in FeMoGaPCBSi bulk glassy alloys

The effect of Cr addition on the glass-forming ability (GFA), the magnetic properties, and corrosion resistance in Fe–Mo–Ga–P–C–B–Si glassy alloys was investigated. In addition to a slight increase of supercooled liquid region from 50to55K, the substitution of a small amount of Fe with Cr was found to be effective for approaching alloy to a eutectic point, resulting in an increase in GFA. By copper mold casting, bulk glassy alloy rods with diameters up to 3mm were produced. These glassy alloys exhibit a rather high saturation magnetization of 0.84–1.11T with good soft-magnetic properties, i.e., low coercive force of 2.3–2.9A∕m, and high effective permeability of 13 360–15 960 at 1kHz under a field of 1A∕m. The passive current density of the glassy alloy rod in 3mass% NaCl solution decreased significantly from 1×102to3×10−1A∕m2 with an increase in Cr content, indicating that the addition of Cr is effective in enhancing the corrosion resistance.

High Sensitivity Micro-fabricated Fluxgate Sensor with a Racetrack Shaped Magnetic Core

We present a micro fluxgate magnetic sensor having solenoid coils and racetrack shaped magnetic core, which was designed to decrease the .operating power and magnetic flux leakage. Electroplated copper coils of <TEX>$6\;{\mu}m$</TEX> thickness and the core of <TEX>$3\;{\mu}m$</TEX> thickness were separated by benzocyclobutane (BCB) having a high insulation and good planarization characters. Permalloy <TEX>$(Ni_{0.8}Fe_{0.2})$</TEX> as a magnetic core was also electroplated under 2000 gauss to induce the magnetic anisotropy. The core had the high DC effective permeability of <TEX>$\~1,300$</TEX> and coercive field of <TEX>$\~0.1$</TEX> Oe. The fabricated fluxgate sensor had the very small actual size of <TEX>$3.0\times1.7\;mm^2$</TEX>. The fluxgate sensor with a racetrack shaped core had the high sensitivity .of <TEX>$\~350$</TEX> V/T at excitation condition of 3 <TEX>$V_{P-P}$</TEX> and 2 MHz square wave. When two fluxgates were perpendicularly aligned in terrestrial field, their two-axis output signals were very useful to commercialize an electronic azimuth compass for the portable navigation system.

Bulk Glassy Fe&amp;ndash;Mo&amp;ndash;Ga&amp;ndash;P&amp;ndash;C&amp;ndash;B&amp;ndash;Si Alloys with High Glass-Forming Ability and Good Soft Magnetic Properties

The effect of Mo and Si additions on the glass-forming ability (GFA) of Fe 77-x Mo x Ga 3 P 10 C 4 B 4 Si 2 alloys was investigated. The addition of 2 at%Mo combined with 2 at%Si was found to be effective for the extension of the supercooled liquid region (ΔT x defined by the difference between glass transition temperature (Tg) and crystallization temperature (T x ). The ΔT x value is 33 K for the Fe 77 Ga 3 P 12 C 4 B 4 alloy, and increases to 60 K for the Fe 75 Mo 2 Ga 3 P 10 C 4 B 4 Si 2 glassy alloy. In addition, this glassy alloy exhibits a high reduced glass transition temperature (Tg/Ti) of 0.6. The large ΔT x and high T g /T l enabled us to prepare the Fe 75 Mo 2 Ga 3 P 10 C 4 B 4 Si 2 bulk glassy alloy successfully with a diameter of 2 mm and high saturation magnetization (I s ) of 1.27 T. The Fe 75 Mo 2 Ga 3 P 10 C 4 B 4 Si 2 glassy alloy also exhibits good soft magnetic properties, i.e., high effective permeability at 1 kHz of 1.1 × 10 4 and low coercive force of 5 A/m.

Particle size influence to the microwave properties of iron based magnetic particulate composites

Using the combination of Gilbert equation and an extended effective medium theory, high frequency intrinsic and effective permeability was calculated for Fe particles in a non-magnetic matrix (epoxy resin). It was found that the microwave properties (the relative complex magnetic permeability) of the composite were influenced by many material properties, such as saturation magnetization (4πMs), crystal anisotropy field (Ha) and electric resistivity (ρ). Experimental results also showed that particle size played an important role in the microwave performance. The effective magnetic permeability is strongly dependent on the particle size of magnetic spheres in the composite. Our theoretical calculation and experimental results have shown that fine Fe particles are promising for the application as microwave absorbers.

자성체 코어 형상에 따른 마이크로 플럭스게이트 센서의 검출 특성

A fluxgate magnetic sensor consists of a solenoid excitation coil, pick-up coil, and magnetic core. We presents the effect of magnetic core shape in a micromachined fluxgate sensor. To observe the performance of fluxgate sensor with magnetic core side width and gap, side width of 125 <TEX>${\mu}{\textrm}{m}$</TEX>, 250 <TEX>${\mu}{\textrm}{m}$</TEX>, and 500 <TEX>${\mu}{\textrm}{m}$</TEX> were designed in a rectangular-ring shaped core and the gaps of 0 <TEX>${\mu}{\textrm}{m}$</TEX>, 50 <TEX>${\mu}{\textrm}{m}$</TEX>, and 100 <TEX>${\mu}{\textrm}{m}$</TEX> were also fabricated in a racetrack shaped core. The solenoid coils and magnetic core were separated by benzocyclobutane(BCB) which had high insulation and good planarization characters. Copper coil patterns of 10 <TEX>${\mu}{\textrm}{m}$</TEX> width and 6<TEX>${\mu}{\textrm}{m}$</TEX> thickness were electroplated on Ti(300 <TEX>$\AA$</TEX>) / Cu(1500 <TEX>$\AA$</TEX>) seed layers. 3 <TEX>${\mu}{\textrm}{m}$</TEX> thick N <TEX>$i_{0.8}$</TEX>F <TEX>$e_{0.2.}$</TEX>(permalloy) film for the magnetic core was also electroplated under 2000 gauss to induce the magnetic anisotropy. The magnetic core had the high DC effective permeability of ∼1,300 and coercive field of ∼0.1 Oe. Because the magnetic cores of 500 <TEX>${\mu}{\textrm}{m}$</TEX> side width and 0 gap had a low magnetic flux leakage, high sensitivity of ∼350 V/T were measured at excitation condition of 3 <TEX>$V_{P-P}$</TEX> and 2 MHz square wave. The power consumption of ∼14 ㎽ was measured. The fabricated fluxgate sensor had the very small actual size of 3.0<TEX>${\times}$</TEX>1.7 <TEX>$\textrm{mm}^2$</TEX>. When two fluxgates were perpendicularly aligned in terrestrial field, their two-axis output signals were very useful to commercialize an electronic azimuth compass for the portable navigation system.m.m.m.

MEMS 공정 제작방법에 의한 솔레노이드형 여자 코일과 검출코일을 사용한 마이크로 플럭스게이트 센서

This paper describes a MEMS-based micro-fluxgate magnetic sensing element using Ni<TEX>$\_$</TEX>0.8/Fe<TEX>$\_$</TEX>0.2/ film formed by electroplating. The micro-fluxgate magnetic sensor composed of a thin film magnetic core and micro-structure solenoids for the pick-up and the excitation coils, is developed by using MEMS technologies in order to take advantage of low-cost, small size and lower power consumption in the fabrication. A copper with 20<TEX>${\mu}$</TEX>m width and 3<TEX>${\mu}$</TEX>m thickness is electroplated on Cr (300<TEX>${\AA}$</TEX>) / Au (1500<TEX>${\AA}$</TEX>) films for the pick-up (42turn) and the excitation (24turn) coils. In order to improve the sensitivity of the sensing element, we designed the magnetic core into a rectangular-ring shape to reduce the magnetic flux leakage. An electroplated permalloy film with the thickness of 3<TEX>${\mu}$</TEX>m is obtained under 2000 gauss to induce magnetic anisotropy. The magnetic core has the high DC effective permeability of ~1,100 and coercive field of ~0.1 Oe. The fabricated sensing element using rectangular-ring shaped magnetic film has the sensitivity of about 150 V/T at the excitation frequency of 2 MHz and the excitation voltage of 4.4 V<TEX>$\_$</TEX>p p/. The power consumption is estimated to be 50mW.

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.

High-frequency permeability characteristics of Fe- and Co-based amorphous alloys with high B concentrations

New Fe-based and Co-based amorphous alloys with a high B concentration of 30 at% were formed in the (Fe,Co,Ni)/sub 62/Nb/sub 8/B/sub 30/ system. The amorphous alloys exhibit a wide supercooled liquid region (/spl Delta/T/sub x/) above 80 K before crystallization in the range of 5 to 40% Co and 0 to 10% Ni and the largest /spl Delta/T/sub x/ is 87 K for Fe/sub 52/Co/sub 10/Nb/sub 8/B/sub 30/. The Fe/sub 62-x/Co/sub x/Nb/sub 8/B/sub 30/ alloys exhibit good soft magnetic properties i.e., low coercive force (H/sub c/) of 2-3 A/m, high effective permeability (/spl mu//sub e/) of 20000-30000 at 1 kHz and low saturated magnetostriction (/spl lambda//sub s/) of 2-8/spl times/10 d. The high /spl mu//sub e/ characteristics are maintained in a higher frequency range and the highest /spl mu//sub e/ at 1 kHz is 7500 for Co/sub 40/Fe/sub 22/Nb/sub 8/B/sub 30/ with a high resistivity of 237 /spl mu//spl Omega/ cm. The finding of the (Fe,Co)/sub 62/Nb/sub 8/B/sub 30/ amorphous alloys exhibiting large /spl Delta/T/sub x/, good high-frequency permeability and high resistivity is encouraging the future development as a new soft magnetic materials.

ナノ結晶Ｆｅ‐Ａｌ‐Ｓｉ‐Ｍ‐Ｂ（Ｍ＝Ｖ，Ｎｂ，Ｔａ）合金薄帯の構造と軟磁気特性

The structures and soft magnetic properties of Fe-Al-Si-M-B (M=V, Nb, Ta) alloy ribbons crystallized from amorphous state were investigated. The ribbons were composed of bccFe(Al, Si) crystallites in the DO3 ordered phase, with a grain diameter of less than 30 nm. These nanocrystalline alloy ribbons showed low saturation magnetostriction below 1 × 10-6 and high effective permeability above 10,000 at 1 kHz after annealing. Soft magnetic properties were obtained in the ribbons, generally in the order of Nb > Ta=V. Fe66Al8Si14Nb3B9 alloy ribbon showed particularly good soft magnetic properties (λs = 0.5 × 10-6, μeff=59,000 at 1 kHz) with good thermal stability.

Nanocrystalline soft magnetic Fe-M-B (M = Zr, Hf, Nb) alloys and their applications

This paper reviews our results on the development of a new type of soft magnetic material with high saturation magnetic flux density (Bs) above 1.5 T as well as excellent soft magnetic properties. A mostly single bcc structure composed of α-Fe grains with about 10–20 nm in size surrounded by a small amount of an intergranular amorphous layer was obtained by crystallization of amorphous alloys prepared by melt-spinning technique. The typical nanocrystalline bcc Fe 90Zr 7B 3, Fe 89Hf 7B 4 and Fe 84Nb 7B 9 ternary alloys subjected to the optimum annealing exhibit high Bs above 1.5 T as well as high effective permeability (μe) at 1 kHz above 20000. Excellent soft magnetic properties of the nanocrystalline Fe-M-B based alloys can be obtained by the decrease in the bcc grain size, magnetostriction (λ) and the increase in Tc of the intergranular amorphous phase by optimizing the crystallization process, chemical composition and adding small amounts of elements. For example, the improved FeZrNbBCu alloy shows the high ue of 160000 combined with the high Bs of 1,57 T. This excellent μe is comparable to those of nanocrystalline Fe 73.5Si 13.5B 9Nb 3Cu 1 and the zero-magnetostrictive Co based amorphous alloys, and the high Bs is comparable to those of the Fe based amorphous alloys with rather good soft magnetic properties. The excellent characteristics of a power transformer, a common mode choke coil, a pulse-transformer and a flux gate magnetic detector made of ‘NANOPERM ™’ were found in agreement with its very low core losses, sufficient thermal stability and low stress-sensibility of magnetic properties. The nanocrystalline Fe-M-B based alloys ‘NANOPERM ™’ is therefore expected to be used for many kinds of magnetic parts and devices.

The magnetic properties of ultrathin Fe-based nanocrystalline alloy obtained by flash annealing

In an effort to obtain soft magnetic materials with excellent high-frequency characteristics, effects of flash annealing on magnetic properties and microstructure in melt-spun Fe-B-Nb-Cu alloy with ultrathin ribbon shape less than 10 μm thickness were investigated. The alloy subjected to optimum annealing treatment showed higher effective permeability and smaller magnetic core loss at 1 MHz than conventionally annealed alloy. The enhanced magnetic properties of the flash-annealed alloy were attributed to the reduced α-Fe phase grain size to 6 nm and the lower remanence ratio of about 0.3 in comparison to the conventionally annealed alloy with the values of 9 nm and 0.7, respectively. The results show that the flash annealing technique was effective in improving the high-frequency soft magnetic properties of Fe-B-Nb-Cu nanocrystalline alloy.

Nanocrystalline Fe–M–B–Cu (M=Zr,Nb) alloys with improved soft magnetic properties

The soft magnetic properties of the nanocrystalline Fe–M–B (M=Zr,Nb) alloys, which exhibit a high saturation flux density (Bs) above 1.5 T as well as a high effective permeability (μe) above 30 000 at 1 kHz, were found to be improved by adding small amounts of Cu and by optimizing the chemical composition. The addition of Cu to the alloys decreases the bcc grain size. The excellent soft magnetic properties (a high μe of 100 000 at 1 kHz combined with a high Bs of 1.53 T) can be achieved in the region where small grain size, as well as nearly zero-magnetostriction are obtained, which is attained in the compositional range around Fe84Nb3.5Zr3.5B8Cu1. The soft magnetic properties can be further improved by low temperature annealing before the crystallization treatment, probably as a result of a decreased grain size distribution in the crystallized state. Consequently, the μe reaches the maximum value of 120 000 for the nanocrystalline Fe84Nb3.5Zr3.5B8Cu1 alloy.