Ge Hongliang

Crystallographic alignment and magnetic anisotropy in melt-spun Nd-Fe-B/α-Fe composite ribbons with different neodymium contents

Abstract Crystallographic alignment and magnetic anisotropy were studied for Nd x Fe 94- x B 6 ( x =8, 9, 10, 11) ribbons prepared via melt-spinning. Effect of Nd content and wheel speed on the crystal structure and magnetic properties of the ribbons was investigated. Both the free and wheel side of the ribbons could obtain strong c -axis crystal texture of Nd 2 Fe 14 B phase perpendicular to the ribbons surface at low wheel speed, but the texture weakened gradually with the increase of the wheel speed. Increase of Nd content led to better formation of crystal texture in the ribbons, indicating that the α-Fe phase might undermine the formation of crystal texture. Magnetic measurement results showed that the magnetic anisotropy of the ribbons exhibited corresponding behavior with the invariance of the c -axis crystal texture of Nd 2 Fe 14 B phase in the ribbons, and the coercivity of the ribbons rose with the increase of both Nd content and wheel speed during melt-spun process.

Study on magnetization reversal behavior for annealed Nd2Fe14B/α-Fe nancomposite alloys

Abstract Effect of thermal annealing on the magnetization reversal behavior of α-Fe/Nd 2 Fe 14 B alloys was investigated. A drastic increase of the remanence M r from 0.67 up to 0.87 T and remanence ratio M r / M s from 0.66 up to 0.76, respectively, was observed in the α-Fe / Nd 2 Fe 14 B alloys annealed at 610 °C as compared with the as-quenched sample. Whereas the further annealing at 680 °C resulted in a strong increase of the corecivity H c as high as 491 kA/m but a slight decrease in M r . The analysis result of the magnetization reversal behavior showed that the maximum value of the integrated recoil loop area about 1.58 kJ/m 3 was obtained in the α-Fe/Nd 2 Fe 14 B alloys at the annealing temperature of 610 °C, significantly lower than other annealed samples. This indicated a significant advantage for the application of this material as permanent magnets in electrical machines and generators due to a low energy loss.

Effect of titanium addition on the magnetic property of Nd2Fe14B/α-Fe nanocomposite alloys

Abstract Rapidly solidified nanocrystalline a-Fe/Nd 2 Fe 14 B alloys with enhanced coercivity were obtained by melt spinning. The effects of Ti addition on the microstructure and magnetic properties of the nanocomposite a-Fe/Nd 2 Fe 14 B alloys were investigated by X-ray diffraction (XRD) and superconducting quantum interference device (SQUID) magnetometer. The analysis of XRD showed that V a-Fe estimated to be about 35.3% in the Ti-free a-Fe/Nd 2 Fe 14 B nanocomposites decreased down to 26.5% as the addition of was 5 at.% Ti. Accordingly, adding Ti resulted in relevant improvements of magnetic properties, especially of the coercivity H c from 595 kA/m up to 1006 kA/m. The dependence of M irrev ( H )/2 M r on the reverse field H indicated that nucleation was the dominating mechanism for the magnetization reversal in these nanocomposites. The analysis of the temperature dependence of the demagnetization curve in the a-Fe/Nd 2 Fe 14 B nanocomposite magnets indicated that a reduction of a ex could play a leading role in an increase in the coercivity of Ti-doped sample.

Effect of niobium addition on magnetization reversal behavior for SmCo-based magnets with TbCu7-type structure

Abstract The effect of Nb addition on the microstructure and magnetic properties of nanocrystalline Sm(Co bal Nb x Zr 0.02 ) 7 permanent magnet were investigated. The magnetization reversal behavior for ball milled Sm(Co bal Nb x Zr 0.02 ) 7 samples with high coercivity was investigated by analyzing hysteresis curves and recoil loops of demagnetization curves. Nb addition proved to result in relevant improvement in the magnetic properties, especially in the coercivity H c . It was shown that the magnetic properties of Sm(Co bal Nb x - Zr 0.02 ) 7 nanocrystalline magnets were improved by an additional 0.06 at.% Nb. In particular, H c was improved from 602 to 786 kA/m at room temperature. The maximum value of the integrated recoil loops area for 0.06 at.% Nb-doped samples of 1.81 kJ/m 3 was much lower than that of the Nb-free sample, which could be explained by a smaller recoverable portion of the magnetization remaining in the Nb-doped sample when the applied field was below the coercivity H c . The nucleation field H n for irreversible magnetization reversal of the magnetically hard phase were calculated by analyzed in terms of the Δ M irrev - H curve and the Kondorsky model.

Preparation and Characterization of Manganese-Zinc Ferrites by a Solvothermal Method

Nickel-zinc ferrites (Ni-Zn ferrites) nanocomposites were prepared by a solvothermal method and characterized by X-ray diffraction (XRD), scanning electronic microscope (SEM) and vibrating sample magnetometer (VSM). The effects of solvothermal parameters such as ratio of Ni2+ to Zn2+, the temperature and the time of solvothermal reaction on the magnetic properties and the microstructures of Ni-Zn ferrites were investigated. Results demonstrate that with raising of reaction time, the particles become bigger and more homogeneous, and the saturation magnetization of the Ni-Zn ferrites nanocomposites get higher; and the formation temperature of Ni-Zn ferrites spherical particles is 180 °C; raising Ni2+ concentration in the Ni-Zn ferrites could not change their morphologies. The saturation magnetization of the Ni-Zn ferrites increases with the increase of Ni2+ in the product; it will reach the highest when Ni2+ concentration is up to x=0.30 while it will be the lowest when Ni2+ concentration is down to x=0.20.

Magnetic properties and magnetization behavior of SmCo-based magnets with TbCu7-type structure

The nanocrystalline magnets with nominal compositions of Sm1–xLuxCo6.8Zr0.2 (x=0, 0.2, 0.4, 0.6) were prepared directly by the intensive milling. The effects of Lu content on the phase structure, the magnetic properties, and magnetization behaviors were also investigated. The XRD patterns of the as-milled samples showed a single SmCo7 phase with TbCu7 structure. Lu addition was proved to result in relevant improvements in the microstructure and magnetic properties, especially in the maximum energy product (BH)max. It was shown that a higher maximum energy product and coercivity of about 17.47 kJ/m3 and 473.45 kA/m were obtained in the sample with x=0.2. From the analysis of the magnetization reversal behavior, it was found that a stronger intergrain exchange coupling interaction was observed in the samples with Lu-doping. From the studies of the coercivity mechanism, it was shown that nucleation model was the dominant magnetization reversal process at the elevated temperature.

Overcoming Decomposition with Order-Reversed Quenching Obtained by Flash Melting

We report on an order-reversed quenching phenomenon in manganese nitrides under flash melting, which prevents the thermodynamically favorable phase transformations from occurring at high temperatures by providing a narrow window of time. The Mn-N kept un-decomposed at high temperatures generated by current up to 339 MA/m2 within 60 ms. After flash melting, the Mn-N shows a significantly enhanced coercivity and a decreased crystalline size. The Mn-N samples decompose rapidly at temperatures above 1100 K with time. The order-reversed quenching technique is potentially useful in processing and preventing phase transformations of meta-stable materials at high temperatures.

Effect of Terbium addition on the coercivity of the sintered NdFeB magnets

Abstract The effects of Tb addition on the microstructure and magnetic properties of the NdFeB magnets prepared by HD method were investigated by X-ray diffraction (XRD) and BH magnetometers. The results of the microstructure showed that both the Tb-doped and undoped permanent magnets were composed mostly of Tetragonal phase Nd 2 Fe 14 B (space group P 42/ mnm ) and a trace amount of Nd-rich phase. Accordingly, addition of Tb led to a decrease of the pole density factor of (004), (006) and (008) crystal plane of the Nd 2 Fe 14 B phase calculated by Horta formula, but the coercivity of the magnets increased from 2038 kA/m up to 2302 kA/m as a consequence of Tb addition. The study of the H c ( T )/ M s ( T ) versus H min N /( M s ( T ) behavior showed that the nucleation was the dominating mechanism for the magnetization reversal in both sintered magnets, and the microstructural parameters of α k and N eff were obtained also. The Kronmuller-plot showed an increase of the α k responsible for an increase of the coercivity.

X-Ray Diffraction Study of Ba6-3x (Eu1/2 Nd1/2)8+2x Ti18O54 Microwave Dielectric Ceramics Prepared by Sol-Gel Method

Abstract Perfectly-sintered Ba 6-3x (Eu 1/2 Nd 1/2 ) 8+2x Ti 18 O 54 ( x = 2/3) (BENT) microwave dielectric ceramics was fabricated successfully with BENT powders prepared by Sol-Gel process. The lattice parameters of BENT ceramic powders were determined by method of X-ray diffraction in ordinary temperature. Orthorhombic lattice type (space group Pbam ) of BENT in ordinary temperature was determined, its pattern was indexed and its polycrystalline X-ray diffraction data were listed. By analysis of its X-ray diffraction data, it could be concluded that Eu and Nd coexisted in the single phase and could not be distinguished in BENT ceramics. The increasing dielectric losses of BENT could be explained basically by the disorder of Eu ions and Nd ions occupied in Al-sites.

Preparation and Properties of Ba6-3xEu8+2xTi18O54 Ceramics via Ethylenediaminetetraacetic Acid Precursor

Abstract Ba 6-3x Eu 8+2x Ti 18 O 54 ( x =2/3) (BET) ceramic powders were synthesized by the Pechini method using ethyl-enediaminetetraacetic acid (EDTA) as a chelating agent. A milk-white, molecular-level, homogeneously mixed gel was prepared, and transferred into a porous resin intermediate through charring. Single-phase and well-crystallized BET ceramic powders were prepared by sintering and smashing ceramics samples, without the formation of any intermediate phases. Meanwhile, the crystal structure, which was determined by X-ray diffraction, had important effect on the microwave dielectric properties of BET. The BET ceramics had good microwave dielectric characteristics: ɛ r = 72.13, Q f = 7111 GHz, τ f = −36.53 × 10 −6 /°C.