Size variation and magnetic dilution effects on the structure and magnetic properties of cobalt zinc ferrite

Nanocrystalline cobalt zinc ferrites Co_1?xZn_xFe₂O₄ (x?=?0.0, 0.2, 0.4, 0.5, 0.6, 0.8, 1.0), have been prepared by employing a precursor combustion method via decomposition of the metal carboxylato hydrazinate precursors. This synthesis technique yields nanoparticles with particle size between 12 and 15 nm as determined from transmission electron microscopy (TEM) studies. The nanoferrites were then sintered at 1000 °C for 15 h to obtain micrometer size ‘bulk’ ferrites in the range of 0.3–0.8 μm. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) Spectroscopy confirmed the formation of the mixed ferrites without any impurities. Addition of non-magnetic ion like Zn²⁺ into the crystal structure of cobalt ferrite leads to a prominent change in the size, structure and properties. The saturation magnetization values (M_S) increases upto x?=?0.4 and then decreases with further increase in Zn concentration. A maximum M_S value of 90.85 emu/g and 79.59 emu/g for x?=?0.4 was obtained for the sintered and nanoferrite sample, respectively. The lower M_S and higher coercivity (H_C) values for nanoferrites than the sintered ferrites exhibited a strong dependence on the particle size due to the cation distribution and surface effects. The Curie temperature (T_C) was found to decrease appreciably with the reduction in particle size and with increasing concentration of Zn. The room temperature Mössbauer spectra showed a transition from ferrimagnetic to a paramagnetic state with increasing zinc concentration along with superparamagnetic features which was in corroboration with VSM studies.

     

锰锌铁氧体非线性磁性能的研究

研究了偏直流磁化对锰锌铁氧体非线性磁性能的影响。研究表明：偏置直流的增加,降低了材料的磁导率,提高了截止频率,并且在一定偏置直流范围内,磁导率呈线性变化。偏置直流磁场的引入,实现了电感量的电流调节和可使用带宽的增加。并且通过对材料烧结工艺的控制,可以在比较大的范围内改变磁导率的调节速度。     

Microstructure and magnetic properties of microwave sintered M-type barium ferrite for application in LTCC devices

M-type barium ferrite material has been widely applied in microwave gyromagnetic devices, but its high sintering temperature restrains its application in chip microwave gyromagnetic devices. In our experiment, single phase barium ferrite has been fabricated at low temperature by microwave sintered (MS) method, the sintering time and temperature were significantly reduced from 22 h and 100 °C for the conventional sintering (CS) process to 2 h and 840 °C for MS process, respectively. Experiments show that MS treated barium ferrite materials possess excellent properties with a saturation magnetization of 53.6 emu/g and coercive force 623.8 Oe. In the frequency range of 1 MHz–1.8 GHz, the real and imaginary part of permeability is between 1.8–3.0 and 0–0.55, and the real and imaginary part of dielectric constant is between 2.4–2.7 and 0–0.15; respectively. Our results indicate that the microwave sintering method is a potential important technique in LTCC technology.     

Influence of copper substitution on magnetic and electrical properties of MgCuZn ferrite prepared by microwave sintering method

Polycrystalline MgCuZn ferrites with chemical formula Mg_0.50-xCu_xZn_0.50Fe₂O₄ (x = 0.00, 0.05, 0.10, 0.15, 0.20, 0.25 and 0.30) were prepared by microwave sintering method. These powders were calcined, compacted and sintered at 950 °C for 30 min. Structural, microstructural and elemental analyses were carried out using X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive X-ray spectrometry (EDS), respectively. The lattice parameter is found to increase with increasing copper content. A remarkable densification is observed with the addition of Cu ions in the ferrites. The sintered ferrite was characterized for initial permeability, dielectric constant and dielectric loss tangent and ac conductivity measurements. The temperature variation of the initial permeability of these samples was carried out from 30 °C to 200 °C. The dielectric constant, dielectric loss tangent and ac conductivity have been measured in the frequency range of 100 Hz to 1 MHz. Initial permeability and dielectric constant were found to increase and dielectric loss decreased with Cu substitution for Mg, up to x = 0.20. The ferrite powder prepared is suitable for the application in multilayer chip inductor due to its low-temperature sinterability, good magnetic properties and low loss at high frequency.     

微波烧结Mn-Zn 铁氧体的微观结构演变特征

以传统氧化物法合成的Mn-Zn铁氧体前驱体和外购前驱体为实验原料,经压制成形后用频率为2.45 GHz的微波在1 200~1 400℃烧结制备Mn-Zn铁氧体软磁材料.对烧结过程样品的微观结构和形貌进行了研究,并探究了烧结过程致密化特性及微波加热温度对Mn-Zn铁氧体密度的影响.研究表明:微波烧结的Mn-Zn铁氧体具有典型的尖晶石结构,样品主体相为Mn0.4Zn0.6Fe2O4;用SEM观察样品形貌,发现在1 350~1 400℃烧结的样品结晶状况良好,晶界平直,烧结组织均匀;微波烧结温度对密度有较大影响,在1 200~1 400℃,随着烧结温度升高样品密度增高,密度为4.80~5.28 g/cm3,在1 400℃烧结样品比较致密.微波烧结可以实现样品的快速致密.     

The effects of magnetic quenching on glassy barium ferrite

Barium ferrite (BaFe₁₂O₁₉) prepared by solution evaporation techniques from ethylene glycol/citric acid or ethylene glycol/pyridine-1-oxide solutions is initially obtained in a glassy form. Although visual observations on samples heated to 1250° C showed that transparency was maintained in thin sections, X-ray powder diffraction studies showed the development of ordered regions of BaFe₁₂O₁₉. Prolonged heating at 1250° C resulted in a loss of visual transparency. Samples of partially amorphous material cooled rapidly in a weak magnetic field were found to have a magnetization considerably higher than samples cooled in the absence of a field. Samples rendered polycrystalline by heating for extended periods at 1250° C showed a lower magnetization on magnetic quenching.     

BaMnZnCoTi-W型铁氧体微波吸收剂的制备和特性研究

对用Ｃｏ２＋、Ｔｉ４＋部分置换Ｆｅ３＋的Ｂａ（ＭｎＺｎ）ａＣｏｂＦｅ１６－ｙＣｏ２＋０．５ｙＴｉ４＋０．５ｙＯ２７－Ｗ型平面六角晶系微波铁氧体吸收剂的制备和特性进行了研究,并对其复介电常数的实部ε′和虚部ε″、磁导率的实部μ′和虚部μ″、损耗随微波频率、Ｃｏ２＋、Ｔｉ４＋含量、涂层厚度的变化作了测试和分析,发现当ｙ＝１．０时铁氧体的吸收性能最佳,其最佳厚度为１．４０ｍｍ,吸收衰减最大达２７．５ｄＢ。     

锰锌铁氧体纳米粒子的制备和磁性能研究

以金属离子的硫酸盐溶液和氨水溶液为原料,采用水热法制备了粒径为6～16nm的锰锌铁氧体纳米粒子.采用XRD、TEM、TGA和VSM等方法对产物以及产物的磁性能进行了表征.结果表明,锰锌铁氧体(Mn1-xZnxFe2O4)的居里温度随着锌的相对含量x的增加而单调的降低.锰锌铁氧体的磁化强度先随着锌的相对含量x的增加而增大,当锌的相对含量＞0.6时,磁化强度随着锌的相对含量x的增加而减小.测量了锰锌铁氧体磁流体的饱和磁化强度,计算了锰锌铁氧体(Mn0.4Zn0.6Fe2O4)纳米粒子的磁矩,其值为1.01×10-19A·m2.     

钴铁氧体纳米粒子制备及其镧掺杂的磁性能研究

为了制备性能良好的钴铁氧体及改善其磁性能,通过改进的溶胶凝胶自蔓延燃烧法成功地制备了钴铁氧体(CoFe2O4)及掺镧(La)钴铁氧体纳米粒子.采用X射线衍射(XRD),透射电镜(TEM)、能谱分析(EDS)、振动样品磁场计(VSM)对所得粒子进行了结构、形貌、成分及磁性能表征.测试结果表明,利用改进的溶胶凝胶法制得钴铁氧体粒度均匀,且成相温度较低,500℃煅烧1h时平均粒径12nm左右;通过掺杂稀土镧元素对所得铁氧体的相结构有较强的影响,所得掺镧钴铁氧体与目标产物一致;所得钴铁氧体具有较高的矫顽力(737.33Oe),并且通过稀土元素镧的掺杂提高了钴铁氧体的矫顽力.     

The role of aggregation of ferrite nanoparticles on their magnetic properties

We have studied the magnetic properties of aggregates of Mn0.5Zn0.5Gd(x)Fe(2-x)O4 ferrite nanoparticles, with x = 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.18, 0.20. The scanning electron microscopy micrographs show significant aggregation of the nanoparticles in all samples. Zero field cooled and field cooled magnetization measurements were conducted on all samples from 400 K down to 5 K. Most zero field cooled curves were found to exhibit the usual behavior but with wide peaked regions. For some x values, the field cooled magnetization was found to increase slowly with decreasing temperature, and becomes nearly constant at low temperatures. The measurements of magnetization versus applied magnetic field were conducted on all samples at 5 K and 305 K in the field range from -15000 to 15000 Oe. At 305 K the magnetization for all samples was observed to saturate, while at 5 K the magnetization did not reach saturation for some values of x. The saturation magnetization values were suggested to be proportional to the size of particles. These results were discussed and suggested to be due to the inter-particle dipolar and exchange interactions between the particles in the aggregates, the large particle size distribution and the surface magnetization effects.     

Effect of proton irradiation on the magnetic properties of manganese ferrite

Cubic-spinel MnFe2O4 magnetic nanoparticles (NPs) were prepared, with an average particle size of about 4 nm determined from a high-resolution transmission electron microscope. When the NPs were proton-irradiated, the lattice constants decreased with increasing proton irradiation. Before the proton irradiation, the NPs exhibited 36.2 +/- 0.1 emu/g magnetization (M(S)) and 11.1 +/- 0.1 Oe coercivity (H(C)). After the irradiation of the samples with 5 and 10 pC/microm2 doses, the M(S) changed to 35.6 and 35.1 +/- 0.1 emu/g, and the H(C) to 11.3 and 12.9 +/- 0.1 Oe, respectively. The room-temperature M?ssbauer spectra of the NPs showed superparamagnetic characteristics, with the single-absorption line of two sites and a large relaxation frequency. During the proton irradiation, the relaxation frequency decreased to 156.02 and 134.29 +/- 0.01 Gamma/? from the unirradiated sample's 164.02 +/- 0.01 Gamma/?. It is suggested that the proton irradiation induced the increase in the anisotropy energy of the MnFe2O4 NPs. Moreover, from the external-field-induced M?ssbauer spectra at 4.2 K, an increase in the canted angle of the hyperfine field between sites A (tetrahedral) and B (octahedral) was observed with proton irradiation.     

纳米晶MnFe2O4的水热法合成及其磁性能

采用水热法制备了软磁材料MnFezO4纳米晶,借助XRD、IR、SEM和VSM对产物进行了表征,着重研究了水热条件如温度和时间等对MnFe2O4纳米晶的形成及其结构和磁性能的影响。结果表明水热温度较低时的产物晶化度和纯度低,表现出较差的磁性能,温度为120℃的产物其饱和磁化强度为15．34emu／g,剩磁比为0．08,矫顽力为8lOe,而在200℃下水热产物饱和磁化强度为51．49emu／g,剩磁比达到0．14,矫顽力为121Oe。     

平面Z-型软磁铁氧体频率特性的研究

研究分析了Co2Z材料显微结构与磁性能的关系,在普通铁氧体工艺中引入预磁化处理方法,并适当控制二次再结晶现象,成功地研制出高性能的Co2Z型宽频材料,Z-型铁氧体材料的共振频率可达1.8GHz以上,截止频率在1GHz附近,起始磁导率在8-13之间,介电常数相对较低(ε'<30)。     

Static magnetic properties of Co and Ru substituted Ba-Sr ferrite

M-type hexagonal ferrite powders, Ba_0.5Sr_0.5Co_xRu_xFe_(12−2x)O₁₉ (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2) have been synthesized by conventional ceramic method. Magnetic properties have been investigated as a function of substitution of Co and Ru ions at applied external field of 10 kOe. XRD and SEM revealed hexagonal structure for these ferrites. The Co and Ru ions substitution cause increase in saturation magnetization and rapid decrease in magnetocrystalline anisotropy at lower substitution. The magnetic parameters variation has been explained by taking into account preferential site occupancy of sublattice sites by substituted ions. Curie temperature decreases with substitution due to weakening of superexchange interaction. The obtained hysteresis parameters suggest that the proposed materials cannot be used for recording applications.