The influences of quenching speed and current annealing on the magnetic properties of Nd9Fe86B5 ribbons were investigated. There is an optimum quenching speed (v ≈ 15 m/s) for preparing hard magnetic ribbons, where t...The influences of quenching speed and current annealing on the magnetic properties of Nd9Fe86B5 ribbons were investigated. There is an optimum quenching speed (v ≈ 15 m/s) for preparing hard magnetic ribbons, where the remanence of 1.22 T, the intrinsic coercivity of 521 kA?m?1 and the energy products of 150 kJ?m?3 are obtained. After annealing ribbons prepared with v = 20 m/s at a dc current of 0.85 A, the remanence reaches a quite large value of 1.47 T, which attributes to the strong exchange coupling interactions between the fine grains of Nd2Fe14B and α-Fe.展开更多
The giant magnetoimpedance effect of the nanocrystalline ribbonFe_(84)Zr_(2.08)Nb_(1.92)Cu_1B_(11) (atom fraction in %) was investigated. There is an optimumannealing temperature (T_A≈ 998 K) for obtaining the larges...The giant magnetoimpedance effect of the nanocrystalline ribbonFe_(84)Zr_(2.08)Nb_(1.92)Cu_1B_(11) (atom fraction in %) was investigated. There is an optimumannealing temperature (T_A≈ 998 K) for obtaining the largest GMI (giant magneto-impedance) effectin the ribbon Fe_(84)Zr_(2.08)Nb_(1.92)Cu_1B_(11). The ribbon with longer ribbon length has strongerGMI effect, which may be connected with the demagnetization effect of samples. The frequencyf_(max), where the maximum magnetoimpedance GMI(Z)_(max) = [(Z(H) - Z(0))/Z(0)]_(max) occurs, isnear the intersecting frequency f_i of the curves of GMI(R), GMI(X), and GMI(Z) versus frequency.The magnetoreactance GMI(X) decreases monotonically with increasing frequency, which may be due tothe decrease of permeability. In contrast, with the AC (alternating current) frequency increasing,the inagnetore-sistance GMI(R) increases at first, undergoes a peak, and under then drops. Theincrease of the magnetoresistance may result from the enhancement of the skin effect with frequency.The maximum magnetoimpedance value GMI(Z)_(max) under H = 7.2 kA/m is about -56.18% at f= 0.3 MHzfor the nanocrystalline ribbon Fe_(84)Zr_(2.08)Nb_(1.92)Cu_1B_(11) with the annealing temperatureT_A= 998 K and the ribbon length L = 6 cm.展开更多
The giant magneto-impedance (GMI) effect associated with the variation of transverse permeability for the ribbons Fe89Zr6Hf1B4 with different annealing temperatures T-A = 793, 823, 893, 923, 993, and 1033 K was invest...The giant magneto-impedance (GMI) effect associated with the variation of transverse permeability for the ribbons Fe89Zr6Hf1B4 with different annealing temperatures T-A = 793, 823, 893, 923, 993, and 1033 K was investigated. There is an optimum annealing temperature TA = 993 K for obtaining the largest GMI effect for the ribbons Fe89Zr6Hf1B4. The magneto-impedance GMI (Z) = (Z(H) - Z(0))/Z(0) for the ribbon with T-A = 993 K can reach -55.09% at a frequency f = 900 kHz under H = 7162 A/m. The relative changes of the real part of transverse permeability Delta mu'/mu'(0) = (mu'(H)- mu'(0))/mu'(0) under H = 7162 A center dot m(-1) at f = 1 MHz are -78.83%, -89.98% and -94.77 % for Fe89Zr6Hf1B4 ribbons with T-A = 823, 893, and 993 K, respectively. The strong GMI effect is accompanied by the large change of transverse permeability. A large magnetoreaetance GMI(X) = (X (H) - X (0))/X (0) of -81.09% can be obtained at f = 100 kHz under H = 7162 A/m for the ribbon with T-A = 993 K. Meanwhile, this present result gave an experimental support to the previous concept / assumption that the positive peak in the field dependence of magneto-impedance is connected to the peak of transverse permeability with varying fields.展开更多
The amorphization and magnetic properties of Fe_(62)Nb_(38) mechanicallyalloyed powders were investigated. In the initial mechanical alloying processes, the latticestructure of pure Fe is destroyed due to the cold-wel...The amorphization and magnetic properties of Fe_(62)Nb_(38) mechanicallyalloyed powders were investigated. In the initial mechanical alloying processes, the latticestructure of pure Fe is destroyed due to the cold-welding and fracturing, accompanying the reductionof ferromagnetic properties. The M_S value of Fe_(62)Nb_(38) powders with ball-milling time t = 6 his only 48.1 A·m^2/kg. With prolongating of mechanical alloying processes, a solid stateamorphization reaction (SSAR) takes place and the Fe-Nb ferromagnetic amorphous phase is formed.With the milling time increasing from 6 to 18 h, the saturation magnetization of Fe_(62)Nb_(38)powders increases with enhancement of the proportion of ferromagnetic amorphous phase in milledpowders. The M_S value of the Fe_(62)Nb_(38) amorphous powders is 98 A·m^2/kg, which is very closeto the value estimated from dilute model. However, the Curie temperature of the Fe_(62)Nb_(38)amorphous phase is only 206℃, which is much smaller than that of the pure Fe. This implies that theexchange interaction between Fe atoms in amorphous alloyed Fe_(62)Nb_(38) becomes weak due to theNb dilution. Investigation shows that the variation of magnetic properties of milled powders is oneof important tools for describing the amorphization by mechanical alloying.展开更多
基金This work was financially supported by the Hi-Tech Research and Development Program (863 Program) of China (No. 2002AA302602 and No. 2001AA324010).
文摘The influences of quenching speed and current annealing on the magnetic properties of Nd9Fe86B5 ribbons were investigated. There is an optimum quenching speed (v ≈ 15 m/s) for preparing hard magnetic ribbons, where the remanence of 1.22 T, the intrinsic coercivity of 521 kA?m?1 and the energy products of 150 kJ?m?3 are obtained. After annealing ribbons prepared with v = 20 m/s at a dc current of 0.85 A, the remanence reaches a quite large value of 1.47 T, which attributes to the strong exchange coupling interactions between the fine grains of Nd2Fe14B and α-Fe.
基金This work was financially supported by the National Natural Science Foundation of China (No. 50271036)
文摘The giant magnetoimpedance effect of the nanocrystalline ribbonFe_(84)Zr_(2.08)Nb_(1.92)Cu_1B_(11) (atom fraction in %) was investigated. There is an optimumannealing temperature (T_A≈ 998 K) for obtaining the largest GMI (giant magneto-impedance) effectin the ribbon Fe_(84)Zr_(2.08)Nb_(1.92)Cu_1B_(11). The ribbon with longer ribbon length has strongerGMI effect, which may be connected with the demagnetization effect of samples. The frequencyf_(max), where the maximum magnetoimpedance GMI(Z)_(max) = [(Z(H) - Z(0))/Z(0)]_(max) occurs, isnear the intersecting frequency f_i of the curves of GMI(R), GMI(X), and GMI(Z) versus frequency.The magnetoreactance GMI(X) decreases monotonically with increasing frequency, which may be due tothe decrease of permeability. In contrast, with the AC (alternating current) frequency increasing,the inagnetore-sistance GMI(R) increases at first, undergoes a peak, and under then drops. Theincrease of the magnetoresistance may result from the enhancement of the skin effect with frequency.The maximum magnetoimpedance value GMI(Z)_(max) under H = 7.2 kA/m is about -56.18% at f= 0.3 MHzfor the nanocrystalline ribbon Fe_(84)Zr_(2.08)Nb_(1.92)Cu_1B_(11) with the annealing temperatureT_A= 998 K and the ribbon length L = 6 cm.
基金This project was financially supported by the National Natural Science Foundation of China (No. 50271036).
文摘The giant magneto-impedance (GMI) effect associated with the variation of transverse permeability for the ribbons Fe89Zr6Hf1B4 with different annealing temperatures T-A = 793, 823, 893, 923, 993, and 1033 K was investigated. There is an optimum annealing temperature TA = 993 K for obtaining the largest GMI effect for the ribbons Fe89Zr6Hf1B4. The magneto-impedance GMI (Z) = (Z(H) - Z(0))/Z(0) for the ribbon with T-A = 993 K can reach -55.09% at a frequency f = 900 kHz under H = 7162 A/m. The relative changes of the real part of transverse permeability Delta mu'/mu'(0) = (mu'(H)- mu'(0))/mu'(0) under H = 7162 A center dot m(-1) at f = 1 MHz are -78.83%, -89.98% and -94.77 % for Fe89Zr6Hf1B4 ribbons with T-A = 823, 893, and 993 K, respectively. The strong GMI effect is accompanied by the large change of transverse permeability. A large magnetoreaetance GMI(X) = (X (H) - X (0))/X (0) of -81.09% can be obtained at f = 100 kHz under H = 7162 A/m for the ribbon with T-A = 993 K. Meanwhile, this present result gave an experimental support to the previous concept / assumption that the positive peak in the field dependence of magneto-impedance is connected to the peak of transverse permeability with varying fields.
文摘The amorphization and magnetic properties of Fe_(62)Nb_(38) mechanicallyalloyed powders were investigated. In the initial mechanical alloying processes, the latticestructure of pure Fe is destroyed due to the cold-welding and fracturing, accompanying the reductionof ferromagnetic properties. The M_S value of Fe_(62)Nb_(38) powders with ball-milling time t = 6 his only 48.1 A·m^2/kg. With prolongating of mechanical alloying processes, a solid stateamorphization reaction (SSAR) takes place and the Fe-Nb ferromagnetic amorphous phase is formed.With the milling time increasing from 6 to 18 h, the saturation magnetization of Fe_(62)Nb_(38)powders increases with enhancement of the proportion of ferromagnetic amorphous phase in milledpowders. The M_S value of the Fe_(62)Nb_(38) amorphous powders is 98 A·m^2/kg, which is very closeto the value estimated from dilute model. However, the Curie temperature of the Fe_(62)Nb_(38)amorphous phase is only 206℃, which is much smaller than that of the pure Fe. This implies that theexchange interaction between Fe atoms in amorphous alloyed Fe_(62)Nb_(38) becomes weak due to theNb dilution. Investigation shows that the variation of magnetic properties of milled powders is oneof important tools for describing the amorphization by mechanical alloying.
