Enhancement of magnetic properties and thermal stability of nanocrystalline (NdDyTb)12.3(FeZrNbCu)81.7B6.0 alloy with Co substitution

The major drawbacks of Nd-Fe-B magnets are relatively low Curie temperature and poor thermal stability. Ribbons with the near stoichiometric 2:14:1 composition of Nd_10.8Dy_0.75Tb_0.75Fe_79.7-xCo_xZr_0.8Nb_0.8Cu_0.4B_6.0 (x=0, 3, 6, 9, 12, 15) were prepared by rapid quenching and subsequent heat treatment. The effect of Co element on the magnetic properties, thermal stability, and microstructure of the ribbons was systematically studied by vibrating sample magnetometer (VSM), thermal magnetic analysis, atomic force microscopy (AFM), and transmission electron microscopy (TEM). It was found that Co substitution was significantly effective in improving the magnetic properties and the thermal stability of nanocrystalline ribbons. Although the intrinsic coercivity decreased from 1308.7 kA/m for x=0 to 817.4 kA/m for x=15, the remanence polarization and maximum energy product increased from 0.839 T and 116.5 kJ/m3 for the Co-free samples to 1.041 T and 155.1 kJ/m3 for the 12at% Co-substituted samples, respectively. About 10 K increase in Curie temperature was observed for the 2:14:1 phase with 1at% Co substitution. The absolute values of temperature coefficients of induction and coercivity were significantly decreased with Co substitution, which may be attractive for high operational temperature applications. The microstructure of nanocrystalline ribbons was slightly refined with Co substitution.     

Dy对Nd60Fe30Al10磁性能的影响

通过X射线衍射仪、 差热扫描量热仪和振动样品磁强计研究Dy对Nd-Fe-Al非晶合金的热稳定性及磁性能的影响. 结果表明, 加入Dy可提高非晶合金的热稳定性, (Nd_1-xDy_x)₆₀Fe₃₀Al₁₀（x=0,0.1,0.2）非晶合金的剩磁随Dy质量分数的增加呈单调下降趋势, 矫顽力随Dy质量分数的增加而增加. Nd\|Fe\|Al非晶合金的矫顽力来源于稀土元素较大的磁晶各向异性场.      

低熔点元素及合金改性HDDR钕铁硼磁粉的研究进展

氢化-歧化-脱氢-再复合(HDDR)工艺是制备各向异性钕铁硼(NdFeB)磁粉的主要方法.但HDDR磁粉实际矫顽力(H_C)较低,重稀土元素Dy的引入可以显著提高其H_C,经研究发现引入的Dy主要分布于磁体晶界,起调控晶界相的作用:增加晶界厚度,提高磁粉的各向异性场(H_A).但重稀土元素Dy自然资源匮乏且价格昂贵,限制了HDDR磁粉的发展.为减少磁粉中重稀土元素用量、降低成本,研究人员通过晶界扩散低熔点元素及合金来替代重稀土元素Dy,因低熔点物质在扩散过程中呈液相,提高了扩散介质与晶界相的接触面积及扩散系数,有利于其沿晶界扩散并调控晶界相,使磁粉H_C提高.对近些年晶界扩散低熔点元素及合金提高HDDR-NdFeB磁粉H_C的部分研究成果进行了归纳.     

Effect of high magnetic field on the crystallization of NdaFe14B/α-Fe nanocomposite magnets

Nd8.1Dy0.9Fe76.95Co8.55B5.5 nanocomposite magnets annealed with and wxmout a 10,magnetic field were investigated in this article. The ribbons with coexisting amorphous and crystalline phases were selected to do this study. The results of M/Sssbauer spectroscopy revealed that the content of a-Fe increased when annealed in high strength magnetic field. The size of the grains also increased considerably after the application of magnetic annealing. All these led to the decrease of the magnetic properties, especially the coercivity of the ribbons.     

Nd<Subscript>2</Subscript>Fe<Subscript>17</Subscript> nanograins effect on the coercivity of HDDR NdFeB magnets with low boron content

Relationships between the coercivity of hydrogenation disproportionation desorption recombination (HDDR) Nd_12.5Fe_81.5−x Co₆B _x bonded magnets and boron content were investigated. Nd₂Fe₁₇ phase with planar magnetic anisotropy is present in the microstructure when x= 4at%–5.88at%, which does not reduce the coercivity of the bonded magnets. High-resolution transmission electron microscopy (TEM) images show that Nd₂Fe₁₇ phase exists in the form of nanocrystals in the Nd2Fe14B matrix. There is an exchange-coupling interaction between the two phases so that the coercivity of HDDR Nd_12.5Fe_81.5−x Co₆B _x bonded magnets is hardly reduced with a decrease in boron content.     

Effects of annealing temperature on the microstructure and hardness of TiAlSiN hard coatings

TiAlSiN hard coatings were synthesized on high-speed steel using an arc ion enhanced magnetic sputtering hybrid system.The microstructure and hardness of the coatings at different annealing temperatures were explored by means of XRD,TEM,EDAX and Vickers indentation.The as-deposited TiAlSiN coatings were confirmed to be amorphous due to high depositing rate and low deposition temperature during the film growth.The transformation from amorphous to nanocomposites of nano-crystallites and amorphousness were observed after the annealing treatment,the microstructure of TiAlSiN coatings annealed at 800°C and 1000°C were consisted of crystalline hcp-AlN,fcc-TiN and amorphous phase,however,the coatings were only consisted of fcc-TiN and amorphous phase when annealing at 1100°C and 1200°C.Meanwhile,the formation of Al2O3 was detected on the coating surface after annealing at 1200°C and it indicated the excellent oxidation resistance of the TiAlSiN coatings under the present experimental conditions.Furthermore,the average grain size of the TiAlSiN coatings after high temperature annealing even at 1200°C was less than 30 nm and the size increased with the increasing temperature.However,the hardness of the so-deposited coatings with HV0.2N=3300 dramatically decreased with the increase of temperature and reached nearly to the hardness of TiN coatings with HV0.2N=2300.     

Co80+xZr20-x 合金的永磁性能

利用X射线衍射和磁性测量研究Co_80+xZr_20-x（x=0,1,2,3,4）合金、 快淬薄带的结构与磁性. 结果表明, 所有样品的比饱和磁化强度均较大, 且在实验范围内随退火温度的升高而增加; 经750℃热处理2 h后, Co₈₁Zr₁₉样品的比饱和磁化强度达到最大值128 (A·m2)/kg; Co₈₂Zr₁₈快淬样品在25 m/s速率下的矫顽力最大, 为60 kA/m, 根据该样品中Co5Zr相的含量较大可知, Co₅Zr相为Co-Zr合金的硬磁相; 由初始磁化曲线可知, 所有样品的矫顽力机制为成核模型.      

Effect of Co addition on crystallization and magnetic properties of FeSiBPCu alloy

The effects of Co addition on the microstructure,crystallization processes and soft magnetic properties of(Fe1 xCox)83Si4B8P4Cu1(x?0.35,0.5,0.65)alloys were investigated.The experimental results demonstrated that the addition of Co decreased the thermal stability against crystallization of the amorphous phase,and thus improved the heat treatment temperature of this alloy.Fe Co Si BPCu nanocrystalline alloys with a dispersedα0-Fe Co phase were obtained by appropriately annealing the as-quenched ribbons at 763 K for 10 min.Theα0-Fe Co with grains size ranging from 9 to 28 nm was identified in primary crystallization.The coercivity(Hc)markedly increased with increasing x and exhibited a minimum value at x0.35,while the saturation magnetic flux density(Bs)shows a slight decrease.The(Fe0.65Co0.35)83Si4B8P4Cu1nanocrystalline alloy exhibited a high saturation magnetic flux density Bsof 1.68 T,a low coercivity,Hcof 5.4 A/m and a high effective permeability meof 29,000 at 1 k Hz.     

Fe_(78)Si_9B_(13)非晶合金的恒导磁性能

研究了普通退火对Fe78Si9B13非晶合金磁性能的影响.实验发现:当合金内有适当数量的-αFe(Si)晶体相析出时,可形成感生磁各向异性,易磁化方向与带面垂直.经470℃×120 min和480℃×60 min退火后合金呈现良好的恒导磁特性.根据剩磁比Br/B800随退火温度和时间变化的规律,讨论了-αFe(Si)晶体相在表面层和基体内的晶化过程对源于磁弹性耦合作用的横向感生磁各向异性的影响:表面层的先期晶化促进横向感生磁各向异性形成;基体内晶体相析出减弱磁弹性耦合作用.     

Effects of yttrium on the formation and magnetic properties of bulk metallic glassy (Fe,Co)-B-Si-Nb alloys

The bulk metallic glassy (BMG) rods of [(Fe_0.5Co_0.5)_0.72B_0.192Si_0.048Nb_0.04]_100-xY_x (x=0-6) and [(Fe_xCo_1-x)_0.72B_0.192Si_0.048Nb_0.04]₉₆Y₄ (x=0.5-0.8) were prepared by copper mold casting. The structure, thermal stability, and magnetic properties of the samples were studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and vibrating sample magnetometer (VSM). Adding 1at% to 6at% of yttrium, the bulk glassy alloy rods of [(Fe_0.5Co_0.5)_0.72B_0.192Si_0.048Nb_0.04]_100-xY_x(x=0-6) with the diameter of 3 mm were not formed, and the sample with 4at% of yttrium showed less crystalline phase than others. When the Fe/Co atomic ratio was between 5:5 and 7:3, the bulk glassy alloy rods of [(Fe_1-xCo_x)_0.72B_0.192Si_0.048Nb_0.04]₉₆Y₄ (x=0.5-0.8) with the diameter of 2 mm were fabricated. In the (Fe, Co)-B-Si-Nb-Y BMGs, when the Fe content increased, the thermal stability, the supercooled liquid region, and the glass-forming ability (GFA) decreased, but the saturation magnetization (M_s) increased.     

Fe54Pt46纳米薄膜的结构与磁性

采用磁控溅射法在SiO₂〈0001〉基片上制备Fe₅₄Pt₄₆薄膜, 并经过650 ℃原位真空退火1 h. 利用X射线衍射和振动样品磁强计对样品的结构和磁性进行研究. 结果表明, 经过原位真空退火后, 样品发生了无序\|有序相转变, 得到了面心四方结构的L1₀-FePt纳米薄膜. 样品的有序度为0.92, 晶粒尺寸约为10 nm, 样品平行膜面的矫顽力为0.8 MA/m. 当磁场与膜面的夹角为50°时, 矫顽力达到最大值, 这与(111)面为能量最低面相符.      

A new type of longitudinally driven GMI effect of FeCo-based alloy

On investigating the longitudinally driven GMI effect of the DC annealed Fe36Co36Nb4Si4.8B19.2 alloy ribbon, the current density was 3.2×10^7 A/m^2, the GMI effect responds sensitively （the sensitivity is as high as 2440.2%/（A-m^-1）） to weak magnetic field after a 600-second annealing. The experimental result shows that the sensitivity is closely related to annealing current density, driven current frequency and eroded thickness. GMI effect, current annealing, sensitivity, magnetic domain structure     

Structure and magnetic properties of [FePt／Ag]10 multilayer films

[FePt/Ag]10 multilayers were deposited on glass substrates by magnetron sputtering. After being annealed at 550℃ for 30 rain, the coercivities of [FePt/Ag]10 multilayer films were observably improved. Magnetic properties of[FePt/Ag]10 multilayer films are influenced by the Ag content. The highest coercivity is obtained for those multilayer films that the Ag content is about 25%. The analysis for the remanence curves shows that the lower FePt layer thickness is favorable for decreasing the intergranular interaction. Result of XRD shows that a thick Ag layer can enhance the intensity of FePt(001) peak. A magnetic activation volume of the order of 10^-24 m^3 is obtained by the measurement of magnetic viscosity, showing that it is promising to be ultrahigh density recording media.     

退火温度对FePt薄膜物性的影响

用直流磁控溅射方法和原位退火工艺在玻璃基片上制备了Fe48Pt52纳米薄膜.研究发现,退火温度对FePt膜的微结构和磁特性有很大的影响,退火可以减小颗粒间的磁相互作用,矫顽力随退火温度的升高先急剧增大后减小,600℃退火处理的FePt样品平行膜面方向的矫顽力略大于垂直方向,分别达到了684.4,580.9 kA/m;650℃退火处理的FePt样品在2个方向上都获得了巨大的矫顽力,最大值达到了986.8 kA/m.     

Study of phase separation in Ga25Se75 xTex chalcogenide thin films

The effects of composition and thermal annealing in between glass transition and crystallization temperature on the optical and structural properties of Ga25Se75-xTex were investigated. The glass transition and crystallization temperature of the synthesized samples was measured by non-isothermal DSC measurements. Amorphous thin films of Ga25Se75-xTex glasses were grown onto ultra clean glass/Si wafer (100) substrates using the vacuum evaporation technique. The effect of thermal annealing on the optical gap (Eg) for Ga25Se75-xTex thin films in the temperature range 358-388K is studied. As-prepared and annealed thin films were characterized by X-ray diffraction, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy and optical absorption. Thermal annealing was found to be accompanied by structural effects, which in turn, lead to changes in the optical constants. The optical absorption coefficient (a) for as-deposited and thermally annealed films was calculated from the absorbance data. From the knowledge of absorption coefficient at different wavelengths, the optical band gap (Eg) was calculated for all compositions of Ga25Se75-xTex thin films before and after thermal annealing. Results indicate that allowed indirect optical transition is predominated in as-deposited and thermally annealed thin films. The influence of Te incorporation and thermal annealing in Ga25Se75-xTex thin films results in a gradual decrease in the indirect optical gap, this behaviorcan be explained as increased tailing. The decrease in optical band gap and an increase in absorption coefficient and extinction coefficient with thermal annealing can be attributed to transformation from amorphous to crystalline phase.     

Effects of the grain alignment on the coercivity and its angular dependence for NdCoFeB permanent magnets

The dependence of the macroscopic magnetism for NdCoFeB permanent magnet on the degree of grain alignment has been studied. With an increase in grain alignment degree, the coercivity of the permanent magnet decreases and the remanence increases. The decrease rate of the coercivity is smaller than the increase rate of the remanence. The coercivity H c(θ) increases with increasing angle θ between the applied field and the texture axis, and for the permanent magnets with good grain alignment the increase rate of H c(θ) is large. These experimental results can be interpreted by using the starting field theory of coercivity.     

Effect of cooling rate on the magnetic properties of Fe53Nd37Al10 alloy

The effect of cooling rate on the magnetic properties of the Fe₅₃Nd₃₇Al₁₀ alloy prepared by different methods, i.e., suction casting and melt spinning at different rates, was investigated. The Fe₅₃Nd₃₇Al₁₀ ribbon at the wheel speed of 5 m·s^?1 exhibits the highest coercivity in the samples. Two hard magnetic phases are detected from the hysteresis loops of the 5 m·s^?1 ribbon at all temperatures below room temperature. Their appearance is associated with different exchange coupling interactions, which are between the two kinds of hard magnetic phases or between the hard magnetic phase and the soft magnetic phase.     

Ag/FePt/C薄膜的结构和磁性

采用直流和射频磁控溅射在Si(001)基片上制备Ag/FePt/C薄膜,并将其在不同温度下进行真空热处理,得到了具有高矫顽力的L10-FePt薄膜.利用X射线荧光(XRF)、X射线衍射(XRD)和振动样品磁强计(VSM)研究样品的成分、结构和磁性.结果表明,样品经400℃热处理后发生了无序—有序相转变,以Ag元素为底层可降低有序化温度,添加Ag和C可抑制晶粒生长.随着热处理温度的升高,FePt的晶粒尺寸和矫顽力逐渐增大,经600℃热处理后,样品中FePt的平均晶粒尺寸为14nm,垂直膜面和平行膜面的矫顽力分别为798.16kA/m和762.35kA/m.     

Co66Fe4Mo2Si16B12结构与磁性能的研究

采用铁芯测试仪测得合金样品的初始磁导率随温度的变化曲线,定出居里温度;用磁化强度小角旋转法测量非晶及晶化合金条带的饱和磁致伸缩系数λs;研究了不同温度退火后Co66Fe4Mo2Si16B12合金的磁性.结果表明:Co66Fe4Mo2Si16B12合金经退火后非晶相和剩余非晶相的居里温度随退火温度升高而提高;Co66Fe4Mo2Si16B12合金经高于500℃退火后磁性能变坏,是饱和磁致伸缩系数变大所致.     

非稀土金属及合金化合物改性烧结NdFeB磁体的研究进展

研究发现,烧结钕铁硼(NdFeB)磁体的矫顽力(H_C)、腐蚀性与晶界相成分、微观结构息息相关.传统熔炼添加重稀土元素虽可改善晶界相提高磁体的H_C及抗蚀性,但同时也使添加物均匀地分布于主相,引起稀磁效应并使成本增加.通过晶界添加非稀土物质调控磁体晶界相,可优化晶界相微观结构,提高其电极电位及润湿性,从而在磁体H_C和耐蚀性得以改善的同时,降低磁体中重稀土元素的用量及成本.对近些年晶界添加非稀土金属及合金化合物调控烧结NdFeB晶界相成分、微观结构及其对磁体H_C、抗蚀性影响的部分研究进行了归纳.