双钙钛矿化合物Sr_2FeMoO_6的制备及其电磁特性研究

采用溶胶一凝胶法在不同烧结温度下制备了双钙钛矿结构化合物Sr_2FeMoO_6,研究了烧结温度对样品B位阳离子的有序度和饱和磁化强度的影响,测量了样品电阻率随温度变化的曲线.X射线衍射实验表明,所有样品中无杂相产生,晶体结构均为四方结构.样品的有序度随烧结温度的升高而增大,而有序度越高的样品饱和磁化强度也越大;样品在30000Oe磁场下的导电行为呈现出由半导体导电行为(低温区T≈10～80K)向金属导电行为(高温区了T≈80～300K)的转变.     

Structure and magnetic properties of columnar Fe-N thin films deposited by direct current magnetron sputtering

Columnar Fe-N thin films with thickness ranging from 30 to 150 nm were deposited by direct current magnetron sputtering using an Ar/N2 gas mixture (V(N2)/V(N2+Ar)=5%) on corning glass substrates. The structure, surface morphology and magnetic properties were investigated using X-ray diffractometry(XRD), scanning electron microscopy, atomic force microscopy, transmission electron microscopy(TEM) and superconducting quantum interference magnetometry. XRD investigation shows that Fe-N films exhibit amorphous-like structures; however, TEM measurements indicate the synthesis of mixture phases of α-Fe+ζ-Fe2N+ε-Fe3N in these films. The magnetic anisotropy and coercivity of Fe-N thin films exhibit strong dependence on the film growth behavior and surface morphology. With increasing the height of Fe-N films with column structures, the coercivity increases from 7.96 kA/m to 22.28 kA/m in the direction parallel to the film surface. In perpendicular direction the coercivity only increases slightly from 39.79 kA/m to 43.77 kA/m. However, the values of anisotropy field increase from 0.79×106 to 1.44×106 A/m, which is mainly attributed to the shape anisotropy of elongated columns due to the fact that the difference of magneto-crystalline anisotropy among these Fe-N films is small. The saturation magnetizations of Fe-N films vary with increasing film thickness from 23.5 to 85.1 A-m2/kg.     

Magnetization arrangement of hard magnetic phases and mechanism of magnetization and reversal magnetization of nano-composite magnets

During the process of directional solidification, laser remelting/solidification in the layer on sintered magnets, die-upsetting of cast magnets, or die-upsetting of nano-composites, the arrangements of the easy-magnetization-axes of the hard magnetic phases (Nd₂Fe₁₄B, SmCo₅ or Sm₂Co₁₇ type) in their designed directions have been studied. In Fe-Pt nano-composite magnets, attempts have been taken to promote phase transformation from disordered, soft magnetic A1 to ordered, hard magnetic L1₀ FePt phase at reduced temperatures. The dependence of the magnetization and reversal magnetization processes on the microstructures, involving the morphology and three critical sizes of particles of the FePt nano-composite magnets, are summarized. With the decrease of the nominal thickness of the anisotropic FePt film epitaxially grown on the single crystal MgO (001) substrate, the reversal magnetization process firstly changes from full domain wall displacement to partial magnetic wall pinning related to the morphology change, where the coercive force increases abruptly. The reversal magnetization process secondly changes from magnetic wall pinning to incoherent magnetization rotation associated with the particles being below the first critical size at which multi-domain particles turn into single domain ones, where the coercive force is still increased. And the reversal magnetization mode thirdly changes from incoherent to coherent rotation referred to the second critical size, where the increase of the coercive force keeps on. However, when the particle size decreases to approach the third critical size where the particles turn into the supperparamagnetic state, the coercive force begins to decrease due to the interplay of the size effect and the incomplete ordering induced by the size effect. Meanwhile, due to the size effect, Curie temperature of the ultra-small FePt particles reduces.     

Hysteresis analysis of Co-Ti substituted M-type Ba-Sr hexagonal ferrite

The magnetic, crystallographic properties and grain morphology of synthesized Ba_0.5Sr_0.5Co_xTi_xFe_{(12 − 2x)}O₁₉ ferrite have been investigated by XRD, SEM and VSM. XRD and SEM confirm M-type hexagonal crystal structure. X-ray diffraction indicates expansion of hexagonal unit cell with substitution of Co²⁺ and Ti⁴⁺ ions. The microstructure governs increase in density and intergrain connectivity with substitution. The preferential site occupancy of substituted Co²⁺ and Ti⁴⁺ ions results in rapid decline of anisotropy field, hysteresis loops also revealed same effect of substitution. Coercivity and remanence magnetization can be easily controlled by varying substitution while maintaining high saturation magnetization, making it useful for recording media.     

壳聚糖磁性微球的制备和工艺参数的优化

采用悬浮交联法制取壳聚糖磁性微球,优化了制备工艺。考察了交联剂的种类和用量、反应体系的pH值、壳聚糖与磁核加入量的比值以及搅拌速度等因素对磁球性能的影响。结果表明,戊二醛做交联剂交联强度较大,与甲醛相比,更有利于壳聚糖交联反应生成球形的壳聚糖磁球;反应体系的pH值4.4～6.7为宜;壳聚糖与磁核微粒的加入量的比值为1∶1时最佳;搅拌速度为1400～1600r/min时反应生成的磁性微球粒度较小、粒径较均匀,成球性好。     

退火温度对Fe_(52)Co_(26)Nb_6B_(15)Cu_1合金纳米晶软磁特性及微波磁谱的影响

采用熔体快淬法制备了Fe52Co26Nb6B15Cu1合金非晶薄带,使用非晶晶化法在480、500、550、600、650℃对其进行等温退火处理,后采用机械球磨法将其球磨得到Fe52Co26Nb6B15Cu1合金微细磁粉。结合X射线衍射分析、振动样品磁强计等测试技术研究热处理温度对Fe52Co26Nb6B15Cu1合金纳米晶的微结构及软磁相关性能的影响。在此基础上使用矢量网络分析仪测试并分析了热处理温度对该纳米晶复合材料在500 MHz~18 GHz磁谱的影响。结果表明,通过控制热处理温度可以有效的调控Fe52Co26Nb6B15Cu1合金样品的微结构与软磁性能,进而在较大范围内调整样品的复数磁导率(μ′(2.0~4.2),μ″(1.0~2.5))。     

Ni_（50）Mn_（25＋x）Ga_（25-x）Tb_（0.5）（x=0,1.5,3,4.5,6）合金马氏体相变与磁性能

研究了Ni50Mn25＋xGa25-xTb0.5（x=0,1.5,3,4.5,6）磁性记忆合金马氏体相变行为、饱和磁化强度和磁感生应变。结果表明,随着Mn含量的增加、Ga含量的降低,合金的马氏体相变温度从202 K升高到416 K,饱和磁化强度从700 mT降低到400 mT,最大磁感生应变达到1870ppm。     

Structural transition and magnetic properties of evaporated Fe/Gd multilayers

Fe/Gd multilayers were prepared by alternate vapor deposition of pure Fe and Gd at a rate of 0.01-0.03 nm/s in an ultra-high-vacuum electron-gun evaporation system.The effects of the constituent metal layer thickness on the microstructures and magnetic properties of the films were investigated by low angle X-ray diffraction,transmission electron microscopy,and vibrating sample magnetometer.The experimental results show that a transition from the polycrystalline to amorphous state in the Fe layers occurs with the decrease of Fe layer thickness in the Fe/Gd multilayers.The saturation magnetization of the muitilayers reduces significantly with decreasing Fe layer thickness and increasing Gd layer thickness.A superparamagnetic behavior at room temperature is observed for the [Fe(0.6 nm)/Gd(4.0 nm)]15 multilayer due to the formation of discontinuous Fe layers.     

磁性石墨烯的制备初探

目的制备磁性石墨烯,实现其定向排列,为进一步制备性能良好的热界面材料提供定向导热相。方法采用聚合物包覆和层层组装技术,在石墨烯表面均匀包覆带负电荷的聚磺苯乙烯(PSS)聚电解质层,然后在静电力作用下包覆一层带正电荷的聚二烯丙基二甲基氯化铵(PDDA)聚电解质。最后,借助静电力使带负电荷的磁性Fe3O4纳米粒子在附着有PDDA层的石墨烯表面形成均匀的致密覆盖层,得到磁性石墨烯,并在外磁场作用下使磁性石墨烯进行定向排列。结果采用聚电解质层层组装技术可有效地对石墨烯进行磁性化处理;粉状石墨烯比片状石墨烯定向排列效果明显;以片状石墨烯为原材料的实验条件下,加入聚电解PSS、PDDA的量越多,磁性化效果更佳。结论通过聚电解质层层组装技术可有效地对石墨烯进行磁性化处理,并在磁场作用下实现定向排列。     

磁性多层膜研究进展:理论和实验

详细叙述了磁性多层膜研究的理论和实验进展，在不同的磁性多层膜材料中，大量实验事实证明和理论预示磁性多层膜具有独特的物理性质，如维度磁性、界面各向异性、耦合作用、巨磁阻、层间交换作用振荡和磁性量子隧道效应等等，因而，磁性多层膜是理论研究和技术应用的重要课题。