Mn0.8Zn0.2Fe2O4/MgAl-LDHs复合材料的磁性能和磁热效应

采用共沉淀法将纳米锰锌铁氧体粒子(Mn_0.8Zn_0.2Fe₂O₄)与镁铝双金属氢氧化物(MgAl-LDHs)进行组装合成了磁性纳米镁铝双金属氢氧化物, 并通过TEM、FTIR、DTA、XRD、VSM等方法对其进行表征. 样品的结构分析结果表明, 复合材料具有典型的核壳结构, 镁铝双金属氢氧化物被赋予磁性后并没有改变其层状结构的典型特征. 样品的磁学性能和磁热性能测试结果表明, 铁氧体的含量对复合材料的磁性能和磁热效应起着决定性作用; MgAl-LDHs对铁氧体粒子没有显著的磁屏蔽效应, 复合材料的饱和磁化强度与铁氧体的含量呈正线性相关, 而复合材料的矫顽力随MgAl-LDHs含量的增加呈现先减小后增大的趋势, 但整体变化幅度很小, 同时MgAl-LDHs对铁氧体粒子磁热效应的影响也极小.     

尖晶石型Ni0.8Zn0.2Fe2O4纳米晶体的制备及电磁性能研究

以金属离子的柠檬酸盐为前驱体，通过sol-gel自燃烧的合成方法制备了镍锌铁氧体（Ni0．8Zn0．2Fe2O4）纳米晶体。采用FT-IR、DSC-TG、XRD、TEM波导等方法对产物以及产物的电磁性能进行了表征。结果表明，在前驱体中，金属离子与柠檬酸以络合物的形式存在，凝胶在220℃完成自燃烧反应，随着热处理温度的升高，粉体的粒径逐渐增大，纳米晶体在8-12GHz的测试条件下具有介电损耗与磁损耗，随着涂层厚度的增加，混合媒质的微波反射率逐渐增加，反射率吸收峰随着厚度的增加向低频移动。     

脉冲激光沉积制备外延Ni_(0.8)Zn_(0.2)Fe_2O_4薄膜的应变与磁性能研究

用脉冲激光沉积设备,分别在SrTiO3(001)(STO)和MgO(001)基片上外延生长了单层Ni0.8Zn0.2Fe2O4(NZF)薄膜。经X射线衍射分析,在STO和MgO基片上制备的NZF薄膜均为单一c取向的外延薄膜,由PHI扫描可知薄膜均为四重对称结构。由NZF薄膜的倒易空间图可以计算得到在STO和MgO基片上应变分别为0.0704和-0.0124。分别对不同基片上的NZF薄膜进行磁强计测量可得,在STO基片上沉积的NZF薄膜的面内和面外饱和磁化强度分别为269.6和224.78 emu/cm3,面内和面外的矫顽场分别为2.68×104和4.78×104A/m,在MgO基片上沉积的NZF薄膜的面内和面外饱和磁化强度分别为219.11和180.75 emu/cm3,面内和面外的矫顽场分别为3.46×104和5.32×104A/m。     

Magnetic and dielectric properties of Ni0.8Zn0.2Fe2O4/HDPE composites for high-frequency application

A low loss high-frequency magnetic composite with Ni_0.8Zn_0.2Fe₂O₄ (NZO) ultrafine particles embedded in a high density polyethylene (HDPE) matrix was fabricated by using a simple low-temperature hot-pressing technique. The magnetic and dielectric properties of the as-prepared composites were investigated in details. The results indicate that as the volume of the ceramic fillers increase, the permittivity, permeability, dielectric and magnetic loss of the composite all increase. The cut-off frequencies of the composites are all above 1 GHz. Because of the low resistivity of NZO, the dielectric losses of the composites are big and decrease with frequency below 100 MHz. Good frequency stabilities of the permittivities and permeabilities, and low dielectric and magnetic losses within the measurement range have been observed. For the composite containing 30 vol% NZO, the permittivity, dielectric loss, permeability and magnetic loss are 3.7, 0.0025, 2.2 and 0.002 at 100 MHz, respectively.     

Synthesis, Structural and Magnetic Properties of Polypyrrole Coated Ni0.2Ca0.8Fe2O4 Nanocomposite

The nanoparticles of spinel ferrites having composition Ni_0.2Ca_0.8Fe₂O₄ were synthesized by an advanced sol-gel method and subsequently coated with intrinsically conducting polypyrrole (PPy) by chemical oxidative polymerization of the corresponding monomer (pyrrole) using ammonium peroxodisulphate as oxidant. The X-ray diffraction and TEM measurements were obtained to understand the crystalline structure, size and morphology of evolution of the samples. The dc electrical investigation revealed that at room temperature the surface conductivity increased from 2.8×10^?5 S?cm^?1 to 1.5×10^?3 S?cm^?1 on polymerization. M?ssbauer investigations revealed that the polymerization causes migration of Fe³⁺ ions from A to B site, resulting to the enhancement of the observed hyperfine field. In agreement with this, the dc magnetization measurements performed on VSM revealed an enhancement in saturation magnetization in the M?CH curves on polymerization. The value of blocking temperature (T _B) is found to have credibly increased from 110 K to 130 K, which confirms the increase in crystallite size after polymerization.     

Electrical and magnetic properties of Ni0.8Zn0.2Fe2O4/silica composite prepared by sol-gel method

Ultrafine Ni_0.8Zn_0.2Fe₂O₄ particles dispersed in silica (SiO₂) matrix are produced by sol-gel method. The powders were subjected to X-ray diffraction to confirm the formation of crystalline phases. The physical properties such as bulk density, true density, % of porosity and % of linear shrinkage were studied. The magnetic permeability as the function of frequency from 1 kHz to 13 MHz and temperatures from room temperature to 300°C were studied for samples sintered at temperature 1250°C. The AC electrical resistivity as the function of frequency and DC electrical resistivity as the function of temperature were studied. The AC-resistivity of the order of 10⁵ cm and DC-resistivity 10⁸ cm were obtained at room temperature. Microstructural features of sintered samples show the presence of ferrite grains of 1–2 m size.     

Effect of Sintering on Magnetic Properties of Ni0.55Zn0.45Fe2O4

Bulk Ni_0.55Zn_0.45Fe₂O₄ samples were obtained by sintering their nanopowder at 1100 ^°C, 1200 ^°C, and 1300 ^°C. Improvement in crystallinity on sintering was identified from increase in intensity of the XRD peaks and grain development in SEM micrographs. Saturation magnetization increased from 81.7 emu/g to 85.3 emu/g as the sintering temperature increased from 1100 ^°C to 1300 ^°C. Initial permeability increases whereas the relative loss factor, resonance frequency, and DC resistivity decreases with increasing the sintering temperature. Curie temperatures obtained from low field AC normalized susceptibility and permeability measurements are in good agreement. The DC resistivity of the samples in the present case is two orders higher than the reported values of samples prepared using conventional ceramic method.     

活性炭负载Co0.8Zn0.2Fe2O4铁氧体的制备及电磁性能研究

采用溶胶-凝胶法制备活性炭负载纳米钴锌铁氧体复合吸波材料研究。以柠檬酸为络合剂制备Co0.8Zn0.2Fe2O4铁氧体溶胶,加入活性炭于溶胶中,经浓缩制得活性炭/钴锌铁氧体凝胶,再经过低温煅烧,制备出形态和结构理想的活性炭负载钴锌铁氧体复合材料;详细地考察烧结温度、煅烧时间及活性炭与铁氧体的配比等工艺参数对复合材料的形态和结构的影响;分别采用X射线衍射(XRD)、扫描电镜(SEM)和能量散射X射线荧光光谱(EDX)对制备出的复合材料进行形貌、结构及组成表征分析。采用波导法在8.2～12.4GHz波段对活性炭负载纳米钴锌铁氧体复合材料进行电磁参数测试分析,结果表明所制备活性炭负载纳米钴锌铁氧体复合材料具有较高的电、磁损耗角正切值,其吸波性能较好。