Effect of Nb and Cr incorporation on the structural and magnetic properties of rapidly quenched FeCoSiB microwires

Rapidly quenched microwires with a nominal composition of Fe₃₉Co₃₉Si₈B₁₄ (#A_O), Fe₃₇Co₃₇Nb₄Si₈B₁₄ (#A_N) and Fe₃₆Co₃₆Nb₄Cr₂Si₈B₁₄ (#A_NC) have been investigated. Devitrification of as-quenched microwires showed that crystallization temperatures increased with simultaneous incorporation of Nb and Cr as in #A_NC alloy. Addition of these elements also contributed to an increase in activation energy in #A_N and #A_NC alloys. Nb addition reduced the particle size, which became much finer in the case of the Cr-containing alloy. Although Nb addition did not have much effect on lowering the Curie temperature T_C of the amorphous phase, Cr substitution lowered T_C to 698 K from high values of 785 K and 787 K observed in the #A_O and #A_NC alloys, respectively. However, the Cr addition revealed a better Giant magneto-impedance (GMI) response compared to the other alloys. Such improved GMI properties in the Cr-containing alloy are attributed to lower values of the coercivity and magnetostriction in the alloy containing both Nb and Cr.     

非晶CoFeNiNbSiB合金的巨磁阻抗效应

研究了非晶Co₇₀Fe_4.5Ni₄Nb₁Si_12.5B₈合金薄带的巨磁阻抗效应.实验表明,在一定频率范围内提高测试频率,磁阻抗效应有明显提高;适当温度的退火也有助于磁阻抗效应的提高.制备态非晶合金样品在频率为5MHz下达120%左右,经过退火处理的非晶样品5MHz下的效应可达400%左右. 关键词：     

Longitudinally driven giant magneto-impedance effect enhancement by magneto-mechanical resonance

Longitudinally driven giant magneto-impedance (GMI) effect in amorphous magnetostrictive Fe₂₄Co_11.82Ni_47.3Si_1.47B₁₅ ribbons was investigated. The experimental results showed that the magneto-mechanical resonance of the ribbons had significantly enhanced GMI effect. The strong magneto-mechanical coupling (MMC) interaction resulted in high MI ratio. Maximal GMI ratio of 1532% was obtained in the sample annealed at 340 °C under transverse magnetic field. The results are explained in terms of MMC and resonance of the magnetostrictive materials.     

Structural and Giant Magneto-impedance properties of Cr-incorporated Co-Fe-Si-B amorphous microwires

The investigation is focused on the effect of Cr incorporation for Co/Fe in (Co_0.5Fe_0.5)_78−xCr_xSi₈B₁₄ (x=0-12) amorphous microwires of 110 μm diameter prepared by in-water quenching technique. The rise in crystallization onset T_X1 with Cr addition revealed the elemental contribution against devitrification and a consequent thermal stability. Cr is unfavorable towards ferromagnetic ordering leading to a linear drop in Curie temperature T_ca with its rise in concentration. The presence of low Cr content upto Cr-4 at.% has been effective in drastically improving the Giant magneto-impedance (GMI) property. Cr content in the range of 4≤X≤10 has low magnetostriction and maximum field sensitivity in the as-quenched state. The GMI properties are further improved after annealing treatment. High content of Cr>10 is found to be deleterious towards GMI behavior and its consequent application as sensor material.     

Soft magnetic properties and giant magneto-impedance effect of Fe73.5−xCrxSi13.5B9Nb3Au1 (x=1–5) alloys

In this paper, the effect of microstructural and surface morphological developments on the soft magnetic properties and giant magneto-impedance (GMI) effect of Fe_73.5−xCr_xSi_13.5B₉Nb₃Au₁ (x=1, 2, 3, 4, 5) alloys was investigated. It was found that the Cr addition causes slight decrease in the mean grain size of α-Fe(Si) grains. AFM results indicated a large variation of surface morphology of density and size of protrusions along the ribbon plane due to structural changes caused by thermal treatments with increasing Cr content. Ultrasoft magnetic properties such as the increase of magnetic permeability and the decrease of coercivity were observed in the samples annealed at 540 °C for 30 min. Accordingly, the GMI effect was also observed in the annealed samples.     

Magnetic domain structure in Fe78.8−xCoxCu0.6Nb2.6Si9B9 nanocrystalline alloys studied by Lorentz microscopy

The magnetic domain structures of Fe_78.8−xCo_xCu_0.6Nb_2.6Si₉B₉ (x=0, 20, 40, 60) alloys are investigated by Lorentz microscopy coupled with the focused ion beam method. The specimen prepared using the FIB method is found to have a considerably more uniform thickness compared to that prepared using the ion-milling method. In Fe_38.8Co₄₀Cu_0.6Nb_2.6Si₉B₉ and Fe_18.8Co₆₀Cu_0.6Nb_2.6Si₉B₉ alloys, 180° domain walls extending in the direction of the induced magnetic anisotropy are observed. Analysis with Lorentz microscopy reveals that the width of the magnetic domains decreases with an increase in the cobalt content or the induced magnetic anisotropy K_u, that is, the domain width d is proportional to the induced magnetic anisotropy (K_u)^−1/4. On the other hand, in the in situ Lorentz microscopy observation as a function of temperature, magnetic ripple structures are found to appear in a localized area due to the fluctuation of magnetization vectors from 423 K. It is observed that the induced magnetic anisotropy caused by the applied magnetic field at 803 K is not suppressed by the magnetic ripple structures observed at 423–443 K.     

High Bs nanocrystalline Fe84−x−yCuxNbySi4B12 alloys (x=0.0-1.4, y=0.0-2.5)

In this study, Cu and Nb content dependences of magnetic properties for annealed Fe_84−x−yCu_xNb_ySi₄B₁₂ alloy ribbons fabricated by melt spinning were investigated. In Fe_83−xCu_xNb₁Si₄B₁₂ alloy systems, the coercivity H_c markedly decreases with increasing x and exhibits a minimum at around x=1.0-1.2, while the saturation magnetic flux density B_s shows a slight variation. In Fe_83−yCu₁Nb_ySi₄B₁₂ alloy systems, H_c markedly decreases at around y=0.5, while B_s shows a monotonic decrease. Fe₈₂Cu₁Nb₁Si₄B₁₂ nanocrystalline alloy ribbons exhibit a high B_s of 1.78 T and a low H_c of 3.2 A/m. The core losses of the present alloys at 1.0 T at 400 Hz, P_10/400, and at 1.0 T at 1 kHz, P_10/1k, are 1.3 and 4.4 W/kg, respectively.     

Effect of Nb addition on the structure and soft magnetic properties of melt-spun Co69Fe7Si14B10 alloy

Melt-spun ribbons of Co₆₉Fe₇Si_14−xNb_xB₁₀ alloys with x=0, 2 and 4 have been prepared and characterized for structure and soft magnetic properties. Ribbons with x=0 and x=2 are found to be completely amorphous whereas the ribbon with x=4 contains irregular shaped faulted Co₂Si orthorhombic phase with grain size of about 100 nm. Nb addition is found to decrease the degree of amorphicity and induce perpendicular anisotropy, deteriorating the soft magnetic and magnetoimpedance properties.     

Stress-MI and domain studies in Co-based nanocrystalline ribbons

A systematic investigation of the influence of different types of annealing on the magnetoimpedance (MI) effect in melt-spun (Co_1−xFe_x)₈₉Zr₇B₄ [x=0, 0.025, 0.05] and (Co_0.88Fe_0.12)_78.4Nb_2.6Si₉B₉Al ribbons has been carried out in the frequency range 500 kHz-13 MHz and under dc magnetic fields (H_dc) up to 80 Oe. In the stress annealed ribbons, the strain-induced transverse anisotropy is seen to result in large MI. Magnetic domains were investigated in the ribbons through magnetic force microscopy.     

Influence of the distance between two voltage contacts on giant magneto-impedance of Co-based amorphous wires

The Co₇₅ Fe_4.2Si₈B₁₂Nb_0.8 amorphous wires of 30 μ m in diameter are produced by melt extraction and annealing at 450 oC for 20 min in vacuum with a longitudinal or transverse field of 40 kA/m. Distances between the two voltage contacts of 6, 5, 4 and 2 mm are obtained by moving the two voltage contacts towards the centre of the sample at the same time. Results indicate that magneto-impedance response is dependent on the distance significantly. As distance decreases from 6 to 2 mm, △Z/Z reduces from 609% to 95% and giant magneto-impedance (GMI) profiles change from two-peak to single-peak. Besides, field sensitivity improves from 0.47%/(A/m) to 0.76%/(A/m) when the single-peak GMI just appears. It is therefore concluded that actual measurements can be made comparable only by taking into account the influence of distance between two voltage contacts for a magneto-impedance measurement.     

Observations of magnetic coupling in Fe-based nanocrystalline alloy by high-temperature giant magneto-impedance effect

The giant magneto-impedance (GMI) effect for Fe_73.5Cu₁Nb₃Si_13.5B₉ nanocrystalline ribbons is investigated in the temperature range between room temperature and 873 K. The thermal dependence of GMI effect reveals the enhancement of Curie temperature of the amorphous matrix, reflecting the exchange coupling between the α-FeSi grains as well as the compositional changes of the amorphous matrix itself. However, the dipolar interaction between grains is suggested to be responsible for the non-zero GMI effect after the magnetic phase transition of the amorphous matrix.     

Influence of Ge on magnetic and structural properties of Joule-heated Co-based ribbons: Giant magnetoimpedance response

Studies of magnetic and structural properties of Fe_3.5Co_66.5Si_12−xGe_xB₁₈ (x=0, 3, and 6) soft magnetic ribbons obtained by melt-spinning were performed. The samples were submitted to Joule-heating treatments with different maximum current values (0.01, 0.05, 0.1, 0.2, and 0.8 A, respectively) with steps of 0.01 A and times by step of 1, 2, and 10 s). X-ray diffraction, temperature dependence of magnetization (for the as-quenched samples), coercivity and giant magnetoimpedance (GMI), measured at different frequencies (100, 500, and 900 kHz, respectively) were performed. All the samples crystallized at annealing currents higher than 0.4 A, which was consistent with the magnetic hardening of the material. Coercivities less than 1 A/m were obtained for the three samples between 0.1 and 0.2 A. Maximum value of GMI response was observed for the sample without Ge in the as-quenched state.     

Giant magnetoimpedance in amorphous (Co0.93Fe0.7)63Ni10Si11B16 glass-coated microwire

Giant magnetoimpedance (GMI) effect has been measured in a glass-coated amorphous (Co_0.93Fe_0.7)₆₃Ni₁₀Si₁₁B₁₆ microwire as a function of DC magnetic field and up to the frequency of 11 MHz. The sample shows single peak GMI characteristics within the whole range of frequency. The domain structure of the above sample has been changed by applying tensile stresses up to 603 MPa and current annealing with a DC current of 50 mA for various time durations, and the corresponding effect on GMI has been studied in detail. A maximum change of 8.85% in MI of the as-quenched sample has been observed around a frequency of 5.05 MHz. Application of an external tensile stress reduces the GMI value by increasing the inner core domain, whereas heat treatment of the sample enhances the same. The square-shaped magnetic hysteresis loop of the as-quenched sample helps us understanding the MI results.     

介观结构对纳米晶软磁合金巨磁阻抗效应影响的理论分析

根据用原子力显微镜对Fe基纳米晶Fe_73.5Cu₁Nb₃Si_13.5B₉合金薄带的介观结构和巨磁阻抗效应的实验研究结果，提出了纳米晶软磁合金巨磁阻抗效应受其介观结构影响的理论模型.该模型成功地解释了低频对纳米晶软磁合金巨磁阻抗效应的影响，反映了现有“三明治”理论的主要特征，并弥补了它的不足；同时指出了纳米晶粒电导率σ、磁导率μ对合金巨磁阻抗效应有影响. 关键词： 铁基纳米晶合金 介观结构 巨磁阻抗效应 介观模型     

Enhancement of giant magneto-impedance effect in Ni80Fe20/SiO2/Cu composite wires

Ni₈₀Fe₂₀/SiO₂/Cu composite wires of Cu core 60 μm in diameter and coated with layers of SiO₂ and Ni₈₀Fe₂₀ were prepared by RF magnetron sputtering. The influences of the insulator layer thickness, the measurement mode and the magnitude of the driving current on the giant magneto-impedance (GMI) effect were investigated. The results showed that there was an optimum thickness of the insulator layer and the driving current can influence the shape of the MI curve. Resonance enhancement of the GMI was found in the new measurement mode. The results are discussed by taking account of the electromagnetic interactions.     

Low temperature magnetization behavior in Co36Fe36Si3Al1Nb4B20 (at%) nanostructured alloy

The investigation addresses low temperature magnetization behavior in Co₃₆Fe₃₆Si₃Al₁Nb₄B₂₀ alloy ribbons in their as-spun as well as annealed state. Optimum heat treatment at 875 K led to nanocrystallization whereby bcc-(FeCo)SiAl nanoparticles were dispersed in an amorphous matrix as evidenced from transmission electron microscopy. Low temperature magnetization studies were carried out in the range 77-300 K. Using the method of mathematical fittings, magnetization extrapolated to 0 K was obtained. The dependence of the magnetization with respect to temperature of BT^3/2 was used to determine the Bloch coefficient “B” and spin wave stiffness constant “D”. Magnetic softening revealed by lowering in the coercivity in the optimum nanostructured state was also the cause of a drop in the stiffness constant. The range of exchange interaction given by D/T_C was higher in the nanostructured state compared to the as-spun amorphous state. The effect of nanocrystallization and the resulting ferromagnetic coupling was further evidenced by low temperature magnetization studies.     

Enhancement in soft magnetic and ferromagnetic ordering behaviour through nanocrystallisation in Al substituted CoFeSiBNb alloys

The effect of substituting Al for Si in Co₃₆Fe₃₆Si_4−xAl_xB₂₀Nb₄, (X=0, 0.5, 1.0, 1.5, 2.0 at%) alloys prepared in the form of melt-spun ribbons have been investigated. All the alloys were amorphous in their as-cast state. The onset of crystallization as observed using differential scanning calorimetry (DSC) was found to rise at low Al content up to X=1 at% beyond which there was a decreasing trend. The alloys also exhibited glass transition at ‘T_g’. Microstructural studies of optimally annealed samples indicated finer dispersions of nanoparticles in amorphous matrix which were identified as bcc-(FeCo)Si and bcc-(FeCo)SiAl nanophases by X-ray diffraction technique. Alloy with optimum content of Al around X=1 at% exhibited stability in coercivity at elevated temperatures. Though Al addition is known to lower magnetostriction, such consistency in coercivity may also be attributed towards lowering in the nanoparticle size compared to X=0 alloy. In the nanostructured state, the alloy containing optimum Al content (X=1) exhibited further enhancement in ferromagnetic ordering or the Curie temperature by 100 K compared to alloy without Al. Such addition also attributed to better frequency response of coercivity and low core losses.     

Effect of quenching wheel speed on the structure, magnetic properties and magnetoimpedance effect in Co64Fe4Ni2B19−xSi8Cr3Alx (x=0, 1 and 2) melt-spun ribbons

Melt-spun ribbons of Co₆₄Fe₄Ni₂B_19−xSi₈Cr₃Al_x (x=0, 1 and 2) alloy at wheel speed of 25 m/s and Co₆₄Fe₄Ni₂B_19−xSi₈Cr₃Al₁ alloy at different wheel speeds (25, 30, 35 and 40 m/s) have been prepared and investigated for structural and magnetic properties and magnetoimpedance effect. Based on the results obtained, it was shown that replacement of B by Al can improve the magnetoimpedance ratio (MIR) and the highest value of MIR (191%) was observed for the sample with X_Al=1 at wheel speed of 25 m/s. Further, it was seen that the higher quenching wheel speed gives rise to a higher coercivity and lower magnetic permeability/MIR value.     

铁基纳米晶合金的介观阻抗率及应用

提出了铁基纳米晶合金介观阻抗率的物理概念,用Maxwell方程组求得其计算公式ρ=-μ{A}/{t}/Δ×H,该式表明铁基纳米晶合金的介观阻抗率与材料内部的介观磁场强度H、介观磁矢势A和介观磁导率μ有关,磁矢势A是由介观结构引起的量子力学效应,是由合金的微观结构决定的.这个理论很好地解释了铁基纳米晶粉末、粉芯 关键词： Fe基纳米晶合金 介观阻抗率     

Large GMI effect in Co-rich amorphous wire by tensile stress

Quality Co₆₈Fe_4.5Si₁₅B_12.5 amorphous wires are fabricated and their giant magneto impedance (GMI) effect are investigated at frequencies ranging from 0.1 to 20 MHz with or without tensile stress applied. Experimental results indicate that the GMI effect of these wires can be effectively improved by applying a small axial tensile stress. There is a pronounced increase from 1.3% to 47.3% in impedance ratio at 0.6 MHz when a stress of 103 MPa is applied. The GMI response is further increased to 261% by doing so at 15 MHz. The field sensitivity of these wires is optimized and it increases from 0.55 to 2.73%/(A/m) at 0.6 MHz and it is proved that the most sensitive field response is obtained by applying a tensile stress of 84.5 MPa below 1 MHz. With reference to the stress evolution of sensitivity at varying frequencies, the maximum field sensitivity shifts to a lower stress with increasing frequency. Quantitatively, a stress as small as 18.4 MPa is enough to yield a field sensitivity as high as 6.7%/(A/m) at 15 MHz. This demonstrates the possibility of achieving small stress (<100 MPa) induced large enhancement of GMI effect and field sensitivity at frequencies of several tens of MHz that are of much technical interest in sensor applications.