Ni-Zn铁氧体纳米晶的机械化学合成

以α－Fe₂O₃、ZnO及NiO粉体为原料,在高能球磨的作用下,通过机械化学反应合成了Ni－Zn铁氧体纳米晶．用XRD、TEM及Mossbauer谱学方法对样品进行了表征．结果表明,球磨所得纳米晶的晶粒尺寸为5～20nm,表现为超顺磁性．经800℃热处理后,晶粒长大到约50nm;表现为亚铁磁性．     

铁素体纤维的损伤与磁性

在铁素体纤维提取工艺理论分析的基础上,研究了提取过程中纤维的损伤机制,提出了提高纤维磁性的工艺措施。结果表明,纤维的损伤机制为氧化反应和置换反应,纤维中的氧、铜和吸附水导致其磁性下降。当mCr/m(Fe+Cr)在13%附近时,通过采取适当的工艺措施,纤维的比饱和磁化强度MS出现极大值(159 emu/g)。     

PZT／Ni－Zn铁氧体复合材料电磁特性研究

研究了铁电材料ＰＺＴ和铁磁材料Ｎｉ－Ｚｎ铁氧体的复合材料在１～１０００ＭＨｚ频率范围内的电磁特性。结果表明，ＰＺＴ具有铁电与铁磁共存的双重特性。当与Ｎｉ－Ｚｎ铁氧体复合后，其复合磁导率及复合介电常数均具有可调性，由此可优化设计高吸收电磁波能力的新型复合材料。     

Structural and Magnetic Studies on Chromium substituted Ni-Zn Nano Ferrite Synthesized by Citrate Gel Auto Combustion Method

Nano crystalline Ni_0.5Zn_0.5Cr_xFe_2?xO₄ particles with x varying from 0.00 to 0.25 in steps of 0.05 have been synthesized through citrate gel autocombustion method. When Ni_0.5Zn_0.5Fe₂O₄ nano particles were annealed at 1000 °C, the crystallite size increased while the lattice constant decreased slightly. For, the Cr³⁺ substituted samples annealed at 1000 °C, the variation in lattice constant, bondlengths, M_e-M_e distances and other structural parameters have been attributed to the dissimilarity in the ionic radius of the displaced (Fe³⁺) ion and the substituted (Cr³⁺) ion. Thermal studies indicated the autocombustion process which is an exothermic reaction between the nitrates salt solutions and the citric acid took place at about a temperature of 400 °C for Ni_0.5Zn_0.5Fe₂O₄. The M-H loops for all samples indicated a soft ferrite nature for all samples. The non-saturated hysteresis loop and high coercivity for the as prepared Ni_0.5Zn_0.5Fe₂O₄ nano particles has been attributed to the core-shell structure of the fine particles. When annealed at 1000 °C the saturation magnetization of Ni_0.5Zn_0.5Fe₂O₄ nano particles increased and attained the bulk value (70emu/gm). The specific saturation magnetization has been observed to decrease with increasing Cr³⁺ substitution and is ascribed to the reduction in the predominant A-B exchange interaction mechanism. By considering the site preferences cations a suitable distribution of the cations among the A & B-sites has been proposed for Ni_0.5Zn_0.5Cr_xFe_2?xO₄ nano particles annealed at 1000 °C and has been verified using the X-ray diffraction line intensity calculations. The FT-IR spectra of the annealed ferrite powders showed two significant absorption bands in the wave numbers around 400 cm^?1 & 580 cm^?1 and an additional shoulder at 360cm^?1. The position and width of the bands have been observed to vary with Cr³⁺ substitution. The results of IR spectra are in support of the proposed cation distribution.     

两种Ni-Zn铁氧体复合材料的烧结性能和射频磁性能*

用sol-gel法获得了两种铁氧体复合材料：以镁橄榄石为基体的Ni-Zn铁氧体复合材料和以MAS为基体的Ni-Zn铁氧体复合材料。比较了这两种复合材料的结晶性能和烧结性能。两种复合材料在射频区（100MHz-1GHz)的磁性能优于纯Ni-Zn铁氧体，这种优于纯Ni-Zn铁氧体的磁性能与复合材料的显微结构密切相关：复合材料中Ni-Zn尖晶石晶粒的尺寸较一般纯Ni-Zn铁氧体晶粒尺寸小一个数量级，晶粒间的磁相互作用较纯铁氧体晶粒间弱。     

M型钡铁氧体及其离子取代复合铁氧体制备现状

总结和详细评述了近年来M型钡铁氧体及其离子取代复合铁氧体超微粉末制备合成领域的一些最新研究进展,如溶胶-凝胶法、有机树脂法、化学共沉淀法、水热法、燃烧合成法、玻璃结晶法、微乳液法等.这些方法是当今合成超微粉末材料的重要方法.     

Optical Properties of Spin-Deposited Nanocrystalline Ni-Zn Ferrite Thin Films Processed by Sol-Gel

Nano crystalline Zn-substituted Ni ferrite films with compositions of Ni_1?xZn_xFe₂O₄ (x = 0.25, 0.50, 0.75) were synthesized by sol–gel spin coating method. The synthesized films were characterized for their structural, morphology, optical, electric, and magnetic properties using x-ray diffraction, scanning electron microscope, UV-Vis spectrometer, two probe resistivity, and vibrating sample magnetometer techniques, respectively. The corresponding results indicate that zinc content has significant effect on physical, magnetic, and optical properties of the ferrite. X-ray diffraction studies of thin films showed that the samples have pure cubic spinel phase. The crystallite size is of the nanoparticles estimated using Debey-Scherrer’s method was found to be in the range of 10.27 to 14.97 nm. The lattice parameter was found to be increased from 8.35 to 8.40 Å with increasing Zn²⁺ contents. The morphology of the thin films depicted the formation of well-developed nano-sized clusters with homogeneous and agglomerated. The optical absorption seen to be affected due to the presence of Zn in Ni-Zn ferrite thin films. Ni-Zn ferrite thin films possess small coercivity and remnant magnetization, which indicates the soft magnetic nature of the material. Electrical resistivity of the films decreases with increasing temperature, suggesting the semiconducting nature of the samples.     

溶胶-凝胶法制备Ni-Zn磁性微晶玻璃陶瓷的研究

采用溶胶－凝胶方法分别制备了Ｎｉ－Ｚｎ铁氧体磁性微粉和含Ｂ－Ｓｉ玻璃的先体溶液。然后用颗粒包覆的方法将磁性微粉用此溶胶包覆起来。从而实现了同银电极共烧。材料的磁性、介电性能测试表明,随玻璃含量的增加,介电常数、介电损耗以及制备在样品上的电感均呈减小趋势;介电常数随温度的升高而增大,低频特性更为明显。ＸＲＤ分析５给出材料的主晶相为尖晶石结构。除此之外还有少量的玻璃相。     

Combustion Synthesis: Effect of Urea on the Reaction and Characteristics of Ni-Zn Ferrite Powders

The purpose of this study was to evaluate the effect of the urea content (fuel) on the reaction and the characteristics of Ni-Zn ferrite powders obtained by combustion synthesis. Several batches were prepared with different fuel contents, ranging from the stoichiometric composition between 20 and 100% (excess), while the desired molar proportion of the metal precursors was kept constant. The solutions were heated on a hot plate and then transferred to a muffle furnace preheated to 700°C, in which ignition took place. The resulting powders were characterized by XRD, BET, SEM, and sedimentation, aided by rotation measured through an optic light. The crystalline hematite (-Fe₂O₃) and Ni-Zn ferrite phases were present in all the compositions studied, and the appearance of the agglomerates varied from soft to hard with increasing urea content. The increased urea content, which promoted a longer flame time, influenced the growth and/or formation of hard agglomerates. After sintering at 1200°C/2 h using the stoichiometric composition, only the spinel structure Ni-Zn ferrite, with homogeneous microstructure, was present.     

Zn2+含量对纳米Ni-Zn铁氧体结构和磁性能的影响

采用喷射-沉淀法成功地制备了纳米晶Ni1-xZnxFe2O4(0≤x≤1.0)铁氧体粉料。通过TG-DSC,XRD,TEM等测试手段分析了其微观结构和形貌,用振动样品磁强计测量其室温下磁性能。结果表明:喷射-共沉淀法制备的粉料颗粒细小均匀、形状完整。600℃下煅烧1.5h,样品晶粒尺寸为30nm左右,平均颗粒尺寸小于100nm。随着Zn2+含量的增加,Ni-Zn铁氧体的晶胞参数逐渐增大。室温下,样品比饱和磁化强度随Zn2+含量增加而增加,当x=0.5mol时,最大比饱和磁化强度Ms为66.8A.m2.kg-1。     

铁酸镍纳米微粉的化学共沉淀法制备及磁性研究

在不同条件下用化学共沉淀法制备了NiFe2O4粉体.利用振动样品磁强计测量了样品在室温下的磁性能;利用X射线衍射确定了粉体的组成、晶粒大小和晶格常数;利用扫描电子显微镜观察了颗粒的形貌.确定了制备NiFe2O4共沉淀粉体的工艺条件.     

M-型超微钡铁氧体粉末制备技术的最新进展

介绍了颗粒磁记录介质发展现状,着重总结、分析了钡铁氧体超细粉末制备技术最新进展,包括溶胶－凝胶法、共沉淀法、微乳液法等最新合成方法。这些方法是合成粒径小于１００ｎｍ的钡铁氧体超微粉末的有效方法。     

Magnetization Studies of Mercury-Cuprates and Its Precursors

The mercury-cuprates such as (Hg, Cr)/Sr-1201 and (Hg, Re)/Sr-1201 were synthesized by encapsulation-technique at 880–920 °C for 12–16 h, and characterized by power XRD, M(T) and M(H). All the precursors (Sr₂CuO₃, Cr_0.30Sr₂CuO _y or Re_0.10Sr₂CuO _y ) were found to be non-superconducting. The samples with optimal composition (Hg_0.70Cr_0.30)Sr₂CuO_4+δ [(Hg, Cr)/Sr-1201] and (Hg_0.90Re_0.10)Sr₂CuO_4+δ [(Hg, Re)/Sr-1201] are superconducting with T_c^onset ~ 58T_{\rm c}^{{\rm onset}} \sim 58 and ∼54 K, respectively. At low temperatures (below 10 K), on cooling in D.C.-magnetic field of 4 kOe, the sample (Hg, Re)/Sr-1201 shows a dramatic decrease in diamagnetic signal. Further, this effect is also faintly reflected in the M(H) curve. Such a behaviour was not observed in the (Hg, Cr)/Sr-1201 cuprates. We ascribe this effect to a field enhanced paramagnetic contribution possibly arising from mixed valent (6+, 7+ dominant) Re ions in the (Hg, Re)/Sr-1201 cuprates.     

Magnetization Studies of Mercury-Cuprates and Its Precursors

The mercury-cuprates such as (Hg, Cr)/Sr-1201 and (Hg, Re)/Sr-1201 were synthesized byencapsulation-technique at 880–920°C for 12–16 h, and characterized by power XRD,M(T) andM(H). All the precursors (Sr₂CuO₃, Cr_0.30Sr₂CuO _y or Re_0.10Sr₂CuO_y) were found to be non-superconducting. The samples with optimal composition (Hg_0.70Cr_0.30)Sr₂CuO_4+δ [(Hg, Cr)/Sr-1201] and (Hg_0.90Re_0.10)Sr₂CuO_4+δ [(Hg, Re)/Sr-1201] are superconducting withT _c ^onset ∼ 58 and ∼ 54 K, respectively. At low temperatures (below 10 K), on cooling in D.C.-magnetic field of 4 kOe, the sample (Hg, Re)/Sr-1201 shows a dramatic decrease in diamagnetic signal. Further, this effect is also faintly reflected in theM(H) curve. Such a behaviour was not observed in the (Hg, Cr)/Sr-1201 cuprates. We ascribe this effect to a field enhanced paramagnetic contribution possibly arising from mixed valent (6+, 7+ dominant) Re ions in the (Hg, Re)/Sr-1201 cuprates.     

非晶丝微磁化线圈磁电阻抗效应研究

本文研究了铁基及钴基非晶态合金丝在由微磁经线圈所产生的轴向交变磁场的作用下所呈现的磁电阻抗效应，经出了一些测试结果，结果表明，微磁化线圈两端的电压信号峰－峰值随轴向外磁场Ｈｅ的增加而单调减少，钴基非晶丝可呈现巨磁电阻抗效应，利用该效应可制成新型磁敏元件及器件。     

Magnetization in Nanocrystalline PLD Zinc Ferrite Thin Films Deposited on Fused Quartz Substrate

The nanocrystalline zinc ferrite (ZnFe₂ O ₄) thin films were grown on the fused quartz substrate using pulsed laser deposition. The effects of atmospheric conditions on structural, magnetic, and morphological properties have been systematically studied using X-ray diffraction, vibrating sample magnetometry, and atomic force microscopy. The films showed textured growth of zinc ferrite for the substrate temperatures at ≥ 600 °C irrespective of the ambient environment. Interestingly, thin films of zinc ferrite showed a magnetic hysteresis loop in contrast to the paramagnetic nature of their bulk counterpart. The value of saturation magnetization (4π M _s) increased from 130 to 360 G when the substrate temperature was increased from room temperature (RT) to 800 °C in the oxygen atmosphere. In the absence of oxygen pressure, the value of 4π M _s is observed to be 330 G for the film deposited at RT and found to increase to a value of 670 G when the film is deposited at 400 °C and the maximum value of 2580 G is observed for the film deposited at 700 °C. However, the value of 4π M _s of 800 °C dropped down to 2000 G.