热处理工艺对尖晶石型Ni0.5Zn0.45Co0.05Fe2O4静磁性能的影响

利用溶胶凝胶法制备了尖晶石型 Ni0.5Zn0.45Co0.05Fe2O4 纳米颗粒,设置了3种热处理工艺,发现随着热处理温度的提高,热处理时间的延长,颗粒长大,静磁性能提高。当热处理温度为800℃,保温8h,材料具有比较好的静磁性能（Ms=30.241Oe,Hc=73.261 emg/g,μi=0.210）。另外,将前驱体在磁场条件下热处理,得到颗粒尺寸比同种热处理工艺未加磁场条件下的大,并且静磁性能有了比较大的提高,其比饱和磁化强度甚至比在更高热处理温度,更长热处理时间下制备的NiZnCo铁氧体大。     

Sintering Temperature Dependence of Evolving Morphologies and Magnetic Properties of Ni0.5Zn0.5Fe2O4 Synthesized via Mechanical alloying

We report on an investigation to unravel morphological and magnetic-property dependence on sintering temperature for samples of Ni_0.5Zn_0.5Fe₂O₄ synthesized via mechanical alloying. The samples were sintered at various sintering temperatures from 800?°C to 1000?°C. The morphology of the samples was studied by means of scanning electron microscopy (SEM); hysteresis and permeability measurement were carried out using a BH hysteresisgraph system and an impedance analyzer, respectively. The morphological studies show a microstructural evolution with the increase of sintering temperature. The relationship between ordered magnetism and the microstructure of the samples show that the important grain-size threshold for the appearance of significant ordered magnetism (mainly ferromagnetism) is about ??0.3???m. We found that two factors sensitively influenced the samples content of ordered magnetism, their ferrite-phase crystallinity degree and the number of grains above the critical grain size.     

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。     

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。     

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(Mn0.8Zn0.2Fe2O4)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.     

Synthesis and Magnetic Properties of Bulk Ferrites Spinels Ni0.5Zn0.5Fe2O4: Experimental an Ab-Initio Study

Polycrystalline Ni_0.5Zn_0.5Fe₂O₄ ferrites have been prepared using the solid-state reaction technique. The structure of ferrite was measured using an X-ray diffractometer (XRD). It is shown that the structure of Ni_0.5Zn_0.5Fe₂O₄ ferrites is a single spinel structure. The magnetic properties of the samples were tested at room temperature by a superconducting quantum interference device (SQUID) to determine magnetic properties versus temperature and applied magnetic field. Based on first-principles spin-density functional calculations, using the Korringa–Kohn–Rostoker method (KKR) combined with the coherent potential approximation (CPA), the ferromagnetic and half-metallic behaviors was observed with LDA (local density approximation) and LDA–SIC (local density approximation-self-interaction correction) approximation.     

Annealing Induced Enhancement in Magnetic Properties of Co0.5Zn0.5Fe2O4 Nanoparticles

In this paper, cobalt zinc ferrite (Co_0.5Zn_0.5Fe₂O₄) nanoparticles (NPs) have been prepared using chemical co-precipitation method. In order to investigate the annealing induced effects on their various physical properties, the prepared samples have been annealed at 500 °C, 650 °C and 1000 °C and then compared with as-prepared sample. X-ray diffraction (XRD) patterns of as-prepared and annealed samples at various temperatures exhibit single phase spinel structure. Enhancement in crystallinity and crystallite size is observed with the increase in annealing temperature. The annealing has also greatly influence the morphology and grain size of prepared NPs. The Co_0.5Zn_0.5Fe₂O₄ NPs have shown remarkable enhancement in magnetic moment with increase in annealing temperature. The bandgap energies of Co_0.5Zn_0.5Fe₂O₄ NPs have been measured via UV Spectrometer and observed to decrease with annealing temperature. FTIR spectra of the samples reveal the presence of both high frequency and low-frequency bands due to tetrahedral and octahedral sites, which corroborate well with the XRD results. The observed characteristics of cobalt zinc ferrite NPs as a function of annealing temperature are the rising contender for many data storage and nanodevice applications. Finally, the genotoxicity of prepared nanoferrites has been checked via comet assay.     

Magnetic Properties of Cu0.48Ni0.52Fe2O4 and Thermal Process of Precursor

The spinel Cu_0.48Ni_0.52Fe₂O₄ was synthesized by calcining Cu_0.48Ni_0.52Fe₂(C₂O₄)₃?5H₂O above 300 °C in air for 1.5 h. The precursor and its calcined products were characterized by thermogravimetry and differential scanning calorimetry, FT-IR, X-ray powder diffraction, and vibrating sample magnetometer. The result showed that magnetic properties of Cu_0.48Ni_0.52Fe₂O₄ were influenced by calcination temperature, and Cu_0.48Ni_0.52Fe₂O₄ obtained at 600 °C had a specific saturation magnetization of 40.0 emu?g^?1. The thermal process of Cu_0.48Ni_0.52Fe₂(C₂O₄)₃?5H₂O below 450 °C experienced two steps which involved, at first, the dehydration of the five crystal water molecules, then decomposition of Cu_0.48Ni_0.52Fe₂(C₂O₄)₃ into cubic Cu_0.48Ni_0.52Fe₂O₄ in air. In the DTG curve, two DTG peaks indicated that precursor experienced mass loss of two steps.     

Trends of Parallel Microstructure and Magnetic Properties Evolution in Co0.5Zn0.5Fe2O4

The present paper reports on an effort to expose and scientifically explain the microstructure–magnetic properties relationship as they evolve with increasing sintering temperature. Mechanical alloying was used to prepare cobalt–zinc ferrite nanoparticles with sintering temperature from 800 to 1,350 °C with 50 °C increment. The microstructure of the samples was observed using a field emission scanning electron microscope, and the magnetic parameters, such as the real permeability and loss factor, were measured at room temperature in the frequency range from 10 MHz to 1.0 GHz using an Agilent 4291B impedance/material analyzer. The B–H hysteresis of the samples was investigated using a MATS-2010SD Static Hysteresisgraph. From the results, the real permeability and loss factor were observed to increase up to 1,250 °C. These increases corresponded to increases in grain size and are mainly due to easier domain wall movement. However, due to zinc loss, \(\mu ^{\prime }\) and \(\mu ^{\prime \prime }\) as well as the saturation induction decreased from 1,300 to 1,350 °C. The coercivity increased up to 850 °C and decreased with increasing temperature. This increasing-to-decreasing coercivity trend corresponded well with the single- to multi-domain grain size transition marked by critical grain size at about 0.13 μm.     

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.     

Ce取代对纳米晶Ni0．5Zn0．5Fe2O4电磁性能的影响

以丙烯酰胺为聚合单体,N,N-亚甲基双丙烯酰胺为网络剂,采用聚丙烯酰胺凝胶法制备了尖晶石型Ni0.5Zn0.5CexFe2-xO4(x=0, 0.05)纳米晶.采用X射线,FT-IR,TEM和波导等方法对产物进行了表征.X射线结果表明,当煅烧温度为600℃时,形成纯相的尖晶石型Ni0.5Zn0.5CexFe2-xO4(x=0,0.05);由透射电镜照片可知Ni0.5Zn0.5Fe2O4平均粒径约为30nm;纳米晶体在8.2～12.4GHz的测试频率范围内具有介电损耗(ε")和磁损耗(μ"),Ni0.5Zn0.5Ceo.05Fe1.95O4的ε" 和μ"均高于Ni0.5Zn0.5Fe2O4,Ni0.5Zn0.5Ce0.05Fe1.95O4的ε"和μ"的最大值分别为0.93和0.15.     

Magnetic Phase-Transition Dependence on Nano-to-Micron Grain-Size Microstructural Changes of Mechanically Alloyed and Sintered Ni0.6Zn0.4Fe2 O 4

The microstructure evolution in several polycrystalline Ni_0.6Zn_0.4Fe₂O₄ samples as a result of a sintering scheme was studied in detail, in parallel with the changes in their magnetic properties. The Ni_0.6Zn_0.4Fe₂O₄ toroidal sample was prepared via mechanical alloying and subsequent molding; the sample with nanometer-sized compacted powder was repeatedly sintered from 600 to 1200 °C with an increment of 25 °C. An integrated analysis of phase, microstructural and hysteresis data pointed to existence of three distinct shape-differentiated groups of B–H hysteresis loops which belong to samples with weak, moderate and strong magnetism (Idza in Mater. Res. Bull. 47:1345–1352, 2012), respectively. The real permeability, μ′, and loss factor, μ″, increased with grain size which increased due to increase in sintering temperature and these two magnetic properties also seem to belong to three value-differentiated groups corresponding to the same temperature ranges found for the B–H groupings. These groupings are tentatively explained using Snoek’s Law.     

Influence of Electric Poling on Pb0.9Bi0.1Fe0.55Nb0.45O3 Multiferroic

This paper analyzes the influence of electric poling on structure, magnetism, and ferroelectricity by temperature-dependent Raman scattering (180 K–500 K), magnetic susceptibility, and ferroelectric measurements on Pb_0.9Bi_0.1Fe_0.55Nb_0.45O₃ (PBFNO) multiferroic. X-ray diffraction (XRD) has confirmed the monoclinic structure for PBFNO sample before and after poling. Rietveld refined XRD for poled and unpoled sample shows the influence of electric poling on Fe-O1, Fe-O2, Nb–O, and Bi-O modes with small variation in the lattice parameters. The unpoled PBFNO exhibits broad and overlapping 10 active modes at room temperature (100 to 1300 cm^?1) at 147, 212, 255, 431, 479, 561, 700, 795, 835, and 1112 cm^?1. In case of a poled sample, Pb–O and Nb–O-Nb modes become more active compared to the unpoled sample. Changes observed in the temperature-dependent magnetic measurements, i.e., ZFC/FC and M-H loop, evidence the poling effects on Fe–O and Nb–O active modes. By poling the improvement in ferroelectric domain, ordering occurs, and it is confirmed by P-E loops. The consequences of numerous investigations on electric poling of PBFNO will provide the foundation for future device development and design.

     

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.     

Magnetic and optical properties of MgAl2O4-(Ni0.5Zn0.5)Fe2O4 thin films prepared by pulsed laser deposition

Thin films composed of MgAl₂O₄ and (Ni_0.5Zn_0.5)Fe₂O₄ ([MA(100-x)-NZFx] films) were grown on fused SiO₂ substrates by pulsed laser deposition. X-ray diffraction measurements revealed that the films were polycrystalline, and that their lattice constant varied linearly with composition, indicating the formation of a solid solution. The film with x=60 was paramagnetic and those with x ≥ 70 were ferromagnetic. The films had a transparency above 75% in the visible range, but the transparency decreased with the x value. The optical band gaps were 2.95, 2.55, 2.30 and 1.89 eV for x=20, 40, 60, 80 and 100, respectively. The Faraday rotation angle increased with x in the visible range, and the film with x=70 exhibited a value of 2000 degrees cm^-1 at 570 nm, which is comparable to the rotation angle of Y₃Fe₅O₁₂. Owing to their high transparency, which extends into the visible range, the [MA(100-x)-NZFx] films can be used in novel magneto-optical devices.