锂铁氧体纳米晶磁性的研究

研究了颗粒平均直径由9.1—860nm范围的锂铁氧体纳米晶的磁性.它们的比饱和磁化强度σ_s随其颗粒尺寸减小而线性减小.测量了样品A(颗粒直径为D=860nm),样品B(D=11.8nm)和样品C(D=9.1nm)的比饱和磁化强度随温度的变化曲线σ(T)和穆斯堡尔谱.发现样品B和C的居里温度比样品A的低50℃.从样品C的σ(T)曲线看,样品C好像由二种磁相所构成.利用超顺磁和表面磁性讨论了样品C的特异磁性. 关键词：     

射频溅射FeTaN纳米晶软磁薄膜结构和磁性

用射频反应溅射制备了FeTaN纳米晶软磁薄膜.研究了薄膜结构和磁性与制备条件的依赖关系.研究发现,当Ta的含量较高时,在N2+Ar混合气氛中易形成沉积态薄膜的非晶结构.适当的热处理后,αFe纳米晶从中晶化生成.薄膜显示出优良的软磁特性 关键词： 纳米晶 软磁性 非晶态     

Ni-Zn铁氧体薄膜的结构和磁性

采用交替溅射方法制备了Ni_Zn铁氧体薄膜，并研究了薄膜成分和制 备条件例如热处理温度、氧分压、膜厚、衬底层等因素对Ni_Zn铁氧体薄膜的影响.实验表明沉积态薄膜为非晶态，经大气中不同温度热处理后得到了尖晶石结构，其主峰为(311)峰 .另外，通过不同条件对Ni_Zn铁氧体薄膜的研究，找到了合适的Ni_Zn铁氧体薄膜的制备条件. 关键词： 薄膜 Ni_Zn铁氧体 交替溅射     

超微晶软磁合金的磁性和结构

简要介绍了新型超微晶软磁合金Ｆｉｎｅｍｅｔ的发展现状及应用，介绍了蜚 晶态合金的晶化概念以及微昌析出对非晶态合金磁性的影响，分析了Ｆｉｎｅｍｅｔ的性能和结构的关系，并探索了Ｆｉｎｅｍｅｔ优异软磁特性的根源。     

镉取代对纳米镍铁氧体结构和磁性的影响

采用湿化学共沉淀法合成了Ni_1-xCd_xFe₂O₄ (0≤x≤0.5)的混合铁氧体,利用X射线衍射对其结构和晶相进行表征．结果表明：随着镉Cd浓度的增加晶格参数逐渐增大．扫描电子显微镜研究微观结构,TG/DTA研究了硫酸共沉淀物．揭示了在650 oC合成铁氧体同时进行分解．测量了纳米粒子的磁化强度和交流磁化率．结果表明,Ni_1-xCd_xFe₂O₄混合铁氧体的磁化率、居里温度和有效磁矩随着镉含量的增加下降。     

通过Ta，Al的添加改进纳米晶FeXN薄膜的结构和磁性

在本次工作中，制备了纳米晶FeAlN和FeTaN薄膜。虽然两种膜都展示了软磁性，但是观察到了不同的单轴各向异性。微结构的测量揭示了Ta的添加导致了N的更高溶解度，并且导致了更大的晶格膨胀和更大的压缩应力。单轴各向异性来源于N原子在a－Fe点阵中的各向异性分布。Al更容易与N发生反应，所以FeAlN膜中的a－Fe比FeTaN中的要纯，并且其应力是张应力。两种薄膜不同的各向异性可以由它们不同的微结构来解释。     

各向同性纳米结构Fe-Pt薄膜的结构和磁性

采用直流溅射和热处理技术制备了两个各向同性的纳米结构Fe-Pt永磁合金薄膜系列,并研究了它们的结构和磁性.研究表明,在富Fe双相纳米结构Fe-Pt永磁合金薄膜中,仅由硬磁的FePt相与软磁的Fe₃Pt相组成;在同一系列中,随Fe层厚度的增加,饱和磁极化强度和剩磁明显增大.由Kelly-Henkel图研究指出,在上述Fe-Pt纳米结构永磁合金薄膜中,磁相互作用主要由近邻纳米晶粒间的铁磁交换相互作用控制. 关键词： 磁性薄膜 纳米结构 矫顽力     

Al-O,C元素添加对FeCo合金薄膜磁性和频率特性的影响

用磁控射频溅射法制备了FeCoAlOC薄膜,研究了Al-O和C元素的添加对FeCo合金薄膜的软磁性和高频特性的影响.随着Al,O,C元素添加量的增加,薄膜微结构发生了由多晶到纳米晶再到非晶状态的转化,软磁性得到提高;薄膜电阻率则由最初的87 μΩ·cm增至900 μΩ·cm,高频特性得到改善: 截止频率最高可达2.9 GHz,低频实部磁导率最高可到达400. 关键词： 纳米晶 非晶 软磁薄膜     

机械合金化制备纳米晶和软磁性

简述机械合金化制备纳米晶和纳米晶磁性特征,以及影响纳米晶磁性的因素。纳米晶磁性主要受尺寸因素和球磨粉末的应力影响。     

磁性薄膜的晶格结构和磁性

采用Monte-Carlo模拟方法对六边形、正方形和三角形晶格结构磁性薄膜的磁学特性及磁畴结构进行了模拟,结果表明,磁性薄膜的磁性特征及其磁相变温度和薄膜结构密切相关并存在临界膜厚,当薄膜厚度大于临界膜厚时薄膜磁性特征稳定.在低温区,不同结构磁性薄膜的磁滞回线均出现台阶现象,结果同相关实验一致.     

Microstructure and magnetic properties of Sn-substituted MnZn ferrites

Sn-substituted MnZn ferrites were prepared by conventional oxide ceramic process. The influences of Sn substitution on microstructure and magnetic properties of MnZn ferrites were investigated. The results indicated that with increase of Sn substitute concentration, the diffraction peaks shifted slightly towards the lower angles and the lattice parameter (a) increased. And at room temperature, the bulk density (d_m), initial permeability (μ_i), saturation magnetic induction (B_s) and electrical resistivity (ρ) of Sn-substituted MnZn ferrites all increased initially and then decreased with the further increase of Sn substitute concentration, while the power losses decreased first and then increased subsequently. Meanwhile, the temperature of secondary maximum peak of μ_i-T curve and the minimum losses moved to lower temperature while the Sn substitute concentration increased. When the content of Sn substitution was 0.3 mol%, at room temperature, the initial permeability, saturation magnetic induction, density and electrical resistivity reached their maxima, while the hysteresis loss (P_h), eddy current loss (P_e) and total losses (P_cv) achieved their minima. The P_h∼T and μ_i-T curves varied contrarily, and due to the contribution of extra eddy current loss (P_e,exc) that was proportional to P_h, the P_e-T curve did not agree with its classical expression. Finally, MnZn ferrite substituted with 0.3 mol% SnO₂ shows the highest initial permeability (3894) and lowest losses (303 kW/m³) at room temperature.     

Perpendicularly oriented barium ferrite thin films with low microwave loss,prepared by pulsed laser deposition

Barium ferrite(Ba M) thin films are deposited on platinum coated silicon wafers by pulsed laser deposition(PLD).The effects of deposition substrate temperature on the microstructure,magnetic and microwave properties of Ba M thin films are investigated in detail.It is found that microstructure,magnetic and microwave properties of Ba M thin film are very sensitive to deposition substrate temperature,and excellent Ba M thin film is obtained when deposition temperature is 910℃ and oxygen pressure is 300 m Torr(1 Torr = 1.3332×10~2Pa).X-ray diffraction patterns and atomic force microscopy images show that the best thin film has perpendicular orientation and hexagonal morphology,and the crystallographic alignment degree can be calculated to be 0.94.Hysteresis loops reveal that the squareness ratio(M_r/M_s) is as high as 0.93,the saturated magnetization is 4004 Gs(1 Gs = 10~4T),and the anisotropy field is 16.5 kOe(1 Oe = 79.5775 A·m~(-1)).Ferromagnetic resonance measurements reveal that the gyromagnetic ratio is 2.8 GHz/kOe,and the ferromagnetic resonance linewith is108 Oe at 50 GHz,which means that this thin film has low microwave loss.These properties make the Ba M thin films have potential applications in microwave devices.     

Mechanical and magnetic properties of nanostructured CoNiP films

The electroplating technique is especially interesting due to its low cost, high throughput and high quality of deposit. Magnetic thin films are extensively used in various electronic devices including high-density recording media and micro electromechanical (MEMS) devices. Due to these potential applications, deposition of magnetic film draws special attention and it needs a cost-effective process. Electro-deposition being cost-effective, in the present work cobalt-based magnetic films were deposited electrochemically and deposition characteristics were studied. Effect of concentration of organic additives such as urea and thiourea in the presence of sodium hypophosphite was studied. Surface characterisation was carried out using X-ray diffractometer (XRD) and scanning electron microscope (SEM). Elemental compositions of the films were studied using atomic absorption spectrometer (AAS) and showed phosphorous content was less than 1%. Samples were subjected to vibrating sample magnetometer (VSM) and studies showed that organic additive has altered magnetic properties of these films. The reason for change in magnetic properties and structural characteristics because of the additives were discussed. Mechanical properties such as residual stress, hardness and adhesion of the films were also examined and reported.     

Influences of Bi2O3 on microstructure and magnetic properties of MnZn ferrite

MnZn ferrites were prepared by conventional oxide ceramic process. The effects of Bi₂O₃ on microstructure and magnetic properties of MnZn ferrites were investigated by means of characterizing the fracture surface micrograph, composition of grain boundary, magnetic properties and density by scanning electron microscope (SEM), energy dispersive X-ray spectroscope (EDS), B-H analyzer and Archimedes method, respectively. The results indicate that Bi₂O₃ mainly segregates and concentrates in the grain boundary regions, promotes solid-state reaction and grain growth, reduces porosity and enhances density. Optimum addition of Bi₂O₃ increases the permeability and saturation magnetic induction, meanwhile ensures the well frequency stability of permeability.     

Combined effect of demagnetizing field and induced magnetic anisotropy on the magnetic properties of manganese-zinc ferrite composites

This work is devoted to the analysis of factors responsible for the high-frequency shift of the complex permeability (μ^?) dispersion region in polymer composites of manganese-zinc (MnZn) ferrite, as well as to the increase in their thermomagnetic stability. The magnetic spectra of the ferrite and its composites with polyurethane (MnZn-PU) and polyaniline (MnZn-PANI) are measured in the frequency range from 1 MHz to 3 GHz in a longitudinal magnetization field of up to 700 Ое and in the temperature interval from −20 °С to +150 °С. The approximation of the magnetic spectra by a model, which takes into account the role of domain wall motion and magnetization rotation, allows one to determine the specific contribution of resonance processes associated with domain wall motion and the natural ferromagnetic resonance to the μ^?. It is established that, at high frequencies, the μ^? of the MnZn ferrite is determined solely by magnetization rotation, which occurs in the region of natural ferromagnetic resonance when the ferrite is in the “single domain” state. In the polymer composites of the MnZn ferrite, the high-frequency permeability is also determined mainly by the magnetization rotation; however, up to high values of magnetizing fields, there is a contribution of domain wall motion, thus the “single domain” state in ferrite is not reached. The frequency and temperature dependence of μ^? in polymer composites are governed by demagnetizing field and the induced magnetic anisotropy. The contribution of the induced magnetic anisotropy is crucial for MnZn-PANI. It is attributed to the elastic stresses that arise due to the domain wall pinning by a polyaniline film adsorbed on the surface of the ferrite during in-situ polymerization.     

Structure and magnetic properties of Co-substituted NiZn ferrite thin films synthesized by the sol-gel process

Co-substituted NiZn ferrite thin films, Ni_0.5Zn_0.5Co_xFe_2−xO₄ (0≤x≤0.2), were synthesized by the sol-gel process. The structure and magnetic properties of Ni_0.5Zn_0.5Co_xFe_2−xO₄ ferrite thin films have been investigated. The diffraction peak shifted towards the lower angle and the lattice parameter increased with Co substitution. There is little influence of Co substitution on the microstructure of NiZn ferrite thin films. The saturation magnetization gradually increases with the increase in Co substitution when x≤0.10, and decreases when x>0.10. Meanwhile, the coercivity initially decreases with the increase in Co substitution when x≤0.10, and increases when x>0.10.     

The structural and magnetic powders prepared by properties of barium ferrite the sol-gel method

In this paper,M-type hexagonal barium ferrite powders are synthesized using the sol-gel method.A dried precursor heated in air is analyzed in the temperature range from 50 to 1200 C using thermo-gravimetric analysis and differential scanning calorimetry.The effects of the additives and the cacinating temperature on the magnetic properties are investigated,and the results show that single-phase barium ferrite powders can be formed.After heat-treating at 950 C for 4h with 3 wt% additive,the coercivity and saturation magnetization are found to be 440 Oe and 57.9 emu/g,respectively.