FePt Magnetic Nanoparticles and Their Assembly for Future Magnetic Media

Magnetic nanoparticles with extremely high anisotropy such as chemically ordered $hbox{L}1_{0}$ phase FePt nanoparticles have been considered one of the best candidates for future magnetic recording media with areal density beyond 1 ${ hbox{Tbit/in}}^{2}$ for either the nanocomposite-film-type heat-assisted magnetic recording (HAMR) media or the self-organized-magnetic-array (SOMA)-type bit patterned media. However, current preparation methods via phase transformation must overcome many obstacles, including particle agglomeration, twinning, and difficulty of easy axis alignment. In this paper, the effort on and promise of the preparation of monodispersed magnetic nanoparticles with high anisotropy by a gas phase condensation method is reviewed and reported. The focus is to review recent progress on the fabrication of monodispersed highly ordered $ hbox{L}1_{0}$ phase FePt nanoparticles without phase transformation, successfully self-assembled and magnetically aligned magnetic nanoparticles for SOMA and HAMR media. The mechanisms for directly forming $hbox{L}1_{0}$ phase FePt nanoparticles during nucleation and growth processes and magnetically aligning these particles are analyzed.      

软磁铁氧体材料在电子变压器中的应用

介绍软磁铁氧本材料的种类及性能和在电子变压器中的应用，对其发展方向也进行了简要描述。     

Magnetic and Transparent Composites by Linking Liquid Crystals to Ferrite Nanoparticles through Covalent Networks

The fabrication of transparent, flexible, and optically homogeneous magnetic composites containing ferrite (Fe₃O₄) nanoparticles, liquid crystals (LCs), and siloxane backbones is reported. The transparent magnets are achieved by covalently bonding LCs to the siloxane backbones and then linking them to dopamine‐functionalized ferrite nanocrystals. They exhibit simultaneous high transparency and strong magnetic properties. A remarkable feature of these films is that the surface morphology of the LC‐attached ferrite films can be tuned by an external magnetic field, demonstrating a striped surface in the direction of the field. We show that the LC‐attached film can act as an alignment layer to orient LCs, enabling the development of LC alignment surfaces on the basis of these nanomagnet–LC polymer composites.     

Ferromagnetic Cobalt Nanoparticles and Their Immobilization on Monomolecular Films and Chemical Templates

Monodisperse Co nanoparticles (NPs), stabilized by organic coating have been synthesized, and their immobilization on a variety of self‐assembled monolayers (SAMs) bearing different terminal groups and on SAM‐based chemical templates has been studied. The NPs had an average diameter of ～10 nm and consisted of hcp cobalt covered by a thin (～1 nm) oxide film. They exhibited pronounced ferromagnetic properties with a blocking temperature above 380 K, which is unusual for the given NP size and is presumably related to the high magnetocrystalline anisotropy associated with the crystallographic perfection of the NPs. The NPs were found to attach selectively to the SAMs bearing the thiol tail group, whereas no stable immobilization to other SAMs, over the electrostatic forces, could be achieved. Finally, based on the results for the individual SAMs, high‐contrast 2D structures of the Co NPs were fabricated on SAM‐based chemical templates on both micro‐ and nanometer length scales. The templates were prepared by irradiation‐promoted exchange reaction lithography, taking an OH‐terminated aliphatic SAMs as the primary template and thiol‐bearing aromatic molecules as the substituents.     

Effects of Ethylenediamine Tetraacetic Acid on the Texture and Magnetic Properties of Barium Ferrite Films

M-type barium ferrite thin films with hexagonal platelets on sapphire were fabricated by spin-coating of precursors. Fourier-transform infrared spectra indicated that bonds between the metal and oxygen were formed at about 500°C. X-ray diffraction showed that the films had preferred c-axis orientation. Surface morphology of the film was investigated by scanning electron microscopy. Textures of the films were influenced by the amount of ethylenediamine tetraacetic acid (EDTA). The film with the least pores and the most c-axis-textured platelet hexagonal grains was obtained when the ratio of EDTA to metal ions was 1.0. At the same time, the magnetic hysteresis loops in directions parallel and perpendicular to the film plane demonstrated that the films were almost isotropic. The maximum coercive forces of 43.23 kA/m in plane and 54.70 kA/m out of plane were achieved when the ratio of the amount of EDTA to metal ions was 0.5. The highest in-plane remanence ratio was 0.32 when the ratio of EDTA to metal ions was 1.5, while the highest out-of-plane value was 0.28 in the other two cases.     

Effect of Heat Treatments on the Structural and Magnetic Properties of La-Co Substituted Strontium Ferrite Films

A sputter-deposited strontium ferrite film with perpendicular anisotropy has been developed. The film, composed of La_0.33Sr_0.67Co_0.25Fe_11.75O₁₉, has been fabricated directly on quartz glass substrates by radio frequency magnetron sputtering with various heat treatments. The structural and magnetic property dependence of those films on heat treatments has also been studied. The optimized condition is the heat treatment of in situ heating at 400°C and post-annealing at 850°C–900°C. When post-annealing temperature exceeds 900°C, parasitic phases of γ-Fe₂O₃ and LaFeO₃ appear and gradually increase; meanwhile, the magneto plumbite phase gradually decreases. High c-axis perpendicularly oriented films with the coercivity (4148 Oe), remanence squareness ratio (0.89) and perpendicular magnetic anisotropy energy density (1.65 × 10⁶ erg/cm³) are achieved, which is attributed to the single magneto plumbite phase with compact platelet grains and almost complete (0 0 l) texture of the c-axis normal to the film plane.     

高频应用的NiZn铁氧体磁性能影响因素研究

讨论了Fe2O3、Co2O3、烧结温度对高频应用的NiZn铁氧体磁性能的影响,实验研究了Fe2O3、Co2O3和烧结温度对起始磁导率μi、饱和磁感应强度Bs、矫顽力Hc及样品密度d的影响规律.结果发现,当x(Fe2 O3)=45％～49％时,μi从11单调增加到17,材料的B.从176 mT单调增加到223 mT;当w(Co2O3)=0.4％～2.0％时,μi从20单调降低到11;烧结温度为1 040～1 120℃时,μi从12增加到19,Hc从1 543 A/m降低到926 A/m,d从4.97 g/cm3增加到了5.12 g/cm3.最后,得到性能较好的高频应用NiZn铁氧体Ni0.96 Zn0.04Fe1.88O4(添加w(Co2 O3)=0.8％,w(CuO)=3％,1 080℃下烧结),μ1=11,Bs=195 mT,Hc=1 238 A/m,d=4.82 g/cm3.     

Influence of Sn<Superscript>4+</Superscript> on Structural and DC Electrical Resistivity of Ni-Zn Ferrite Thick Films

Among the soft ferrites, Ni-Zn ferrite is one of the most versatile ceramic materials because of their important electrical and magnetic properties. These properties were improved by substituting Sn⁴⁺ in Ni-Zn ferrites with chemical composition of Ni _x Zn_1+y?x Fe_2?2y Sn _y O₄ (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0; y = 0.1, 0.2). To achieve homogenous ferrite powder at lower sintering temperature and smaller duration in nano-size form, the oxalate co-precipitation method was preferred as compared to other physical and chemical methods. Using this powder, ferrite thick films (FTFs) were prepared by the screen printing technique because of its low cost and easy use. To study structural behavior, the FTFs were characterized by different techniques. The x-ray diffraction and thermo-gravimetric and differential thermal analysis studies show the formation of cubic spinel structure and ferrite phase formation, respectively. There is no remarkable trend observed in lattice constants for the Sn⁴⁺ (y = 0.1)- and Sn⁴⁺ (y = 0.2)-substituted Ni-Zn ferrites. The bond lengths as well as ionic radii on the A-site of Ni-Zn-Sn ferrites were found to decrease with increasing nickel content. The bond length and ionic radii on the B-sites remained almost constant for Sn⁴⁺ (y = 0.1, 0.2)-substituted Ni-Zn ferrites. The energy dispersive x-ray analysis confirms the elemental analysis of FTFs. The Fourier transform infrared spectra show two major absorption bands near 400 cm^?1 and 600 cm^?1 corresponding to octahedral and tetrahedral sites, respectively, which also confirms the formation of the ferrites. The field emission scanning electron microscopy images shows that the particles are highly porous in nature and located in loosely packed agglomerates. The average particle size of the FTFs lies in the range 20–60 nm. Direct current (DC) resistivity of Ni-Zn-Sn FTFs shows the semiconductor nature. The DC resistivity of Ni-Zn-Sn_0.2FTFs is lower than Ni-Zn-Sn_0.1 FTFs. The DC resistivity is found to decrease with the increase in Ni²⁺ content up to x = 0.6. It increases thereafter for a further increase in Ni²⁺ content up to x = 1.0, and a similar trend is observed for the variations of activation energy with Ni²⁺ content.     

CNTs-TiO2复合薄膜的场发射及其在电离规中的应用

介绍一种制备碳纳米管（CNTs）薄膜的方法—擦涂法。利用这种方法制备了CNTs薄膜以及CNTs-TiO2复合薄膜,对其场发射性能进行了研究,发现CNTs＋（7%～10%（质量比））TiO2复合薄膜的场发射性能与纯CNTs薄膜相比有较大改善,开启电场由2.5V/μm降低到1.3V/μm,阈值电场由4V/μm降低到3.1V/μm,场发射的均匀性与稳定性也有显著的提高。利用CNTs＋7%TiO2薄膜样品作为电离真空规的冷阴极,实现了在2×10-2～3×10-5 Pa范围内的近似线性响应,灵敏度约为3.36Pa-1。这种电离真空规具有体积小、低能耗的特点。     

Robust Ferrimagnetism and Switchable Magnetic Anisotropy in High-Entropy Ferrite Film

Ferrimagnetic insulator materials are the enabling technology for the development of next-generation magnetic devices with low power consumption, high operation speed, and high miniaturization capability. To achieve a high-density memory device, a combined realization of robust saturation magnetization (M_s), controllable magnetic anisotropy, and high resistivity (ρ) are highly demanded. Despite significant efforts that have been made recently, simultaneously achieving significant enhancements in these properties in a soft magnetic insulator material still remains a great challenge, severely limiting their practical application. Herein, a high-entropy strategy in an ultra-thin spinel ferrite (CrMnFeCoNi)₃O₄ film is reported that exhibits concurrently a superior saturation magnetization (M_S = 1198 emu cm⁻³), low coercivity (H_C = 90 Oe), and excellent resistivity (ρ = 1233 Ω cm), as well as switchable magnetic anisotropy. The comprehensive lattice probing and microstructure analysis studies reveal that such desirable ferromagnetic properties originate from the high-quality structurally ordered but compositionally disordered single-crystal epitaxial structure. The switchable magnetic anisotropy demonstrated in the high-entropy ferrite film can be attributed to the new antiferromagnetic rock-salt phase. This work unveils the critical benefits of the high-entropy strategy for magnetic oxide thin films, which opens up new opportunities for the development of high-performance magnetic materials.     

Quantitative Magneto-Optical Imaging for Superconducting Thick Films and Tapes

Practical superconducting thick films and tapes, manufactured in an industrial process, have microscopic inhomogeneities. Quantitative magneto-optical imaging (MOI) is one of the most desirable techniques and provides both local and global information on defects, flux pinning, critical current density J _c, and current distribution. We present, herein, a comparative magneto-optical imaging study of the flux profile in YBa₂Cu₃O_7−δ (YBCO) thick films prepared in two different processes, the laboratory versus the industrial scalable process. The remarkably different flux propagation patterns are the manifestation of their different defect landscapes within these films. A method of determining J _c near zero applied field is also given for locally nonuniform superconducting films, using the quantitative MOI technique.     

氮掺杂SiC厚膜的制备及其热电特性

以Si C超细粉为原料,采用热等离子体PVD(TPPVD)法快速制备了Si C膜,最大沉积速度达到1 38nm /s.为了降低Si C膜的电阻率,提高其热电性能,采用向等离子体中通入N2 的方法对Si C膜进行了掺杂.用扫描电子显微镜、X射线衍射和X射线光电子谱对薄膜的形貌和结构进行了观察和分析.实验测定了Si C膜掺杂前后的热电性能并与Si C烧结体的结果进行比较.实验结果表明:向等离子体中导入N2 是对Si C膜进行掺杂的有效方法,但同时也显著影响Si C膜的形貌、成分和沉积速度.未进行氮掺杂和经过氮掺杂后的Si C薄膜的(S2 /ρ)值在973K时分别达到1 6 0 μW/(m·K2 )和1 0 0 0     

Hybrids of Magnetic Nanoparticles with Double‐Hydrophilic Core/Shell Cylindrical Polymer Brushes and Their Alignment in a Magnetic Field

The synthesis of double‐hydrophilic core/shell cylindrical polymer brushes (CPBs), their hybrids with magnetite nanoparticles, and the directed alignment of these magnetic hybrid cylinders by a magnetic field are demonstrated. Consecutive grafting from a polyinitiator poly(2‐(2‐bromoisobutyryloxy)ethyl methacrylate) (PBIEM) of tert‐butyl methacrylate (tBMA) and oligo(ethylene glycol) methacrylate (OEGMA) using atom‐transfer radical polymerization (ATRP) and further de‐protection yields core/shell CPBs with poly(methacrylic acid) (PMAA) as the core and POEGMA as the shell, which is evidenced by ¹H NMR, gel permeation chromatography (GPC), and dynamic and static light scattering (DLS and SLS). The resulting core/shell brush is well soluble in water and shows a pH responsiveness because of its weak polyelectrolyte core. Pearl‐necklace structures are observed by cryogenic transmission electron microscopy (cryo‐TEM) at pH 4, while at pH 7, these structures disappear owing to the ionization of the core. A similar morphology is also found for the polychelate of the core/shell CPBs with Fe³⁺ ions. Superparamagnetic magnetite nanoparticles have also been prepared and introduced into the core of the brushes. The hybrid material retains the superparamagnetic property of the magnetite nanoparticles, which is verified by superconducting quantum interference device (SQUID) magnetization measurements. Large‐scale alignment of the hybrid cylinders in relatively low magnetic fields (40–300 mT) can easily be performed when deposited on a surface. which is clearly revealed by the atomic force microscopy (AFM) and TEM measurements.     

氮掺杂SiC厚膜的制备及其热电特性

以SiC超细粉为原料,采用热等离子体PVD(TPPVD)法快速制备了SiC膜,最大沉积速度达到138nm/s.为了降低SiC膜的电阻率,提高其热电性能,采用向等离子体中通入N2的方法对SiC膜进行了掺杂.用扫描电子显微镜、X射线衍射和X射线光电子谱对薄膜的形貌和结构进行了观察和分析.实验测定了SiC膜掺杂前后的热电性能并与SiC烧结体的结果进行比较.实验结果表明:向等离子体中导入N2是对SiC膜进行掺杂的有效方法,但同时也显著影响SiC膜的形貌、成分和沉积速度.未进行氮掺杂和经过氮掺杂后的SiC薄膜的(S2/ρ)值在973K时分别达到160μW/(m·K2)和1000μW/(m·K2),是SiC烧结体的5.3倍和33倍.     

LB膜及其应用

本文介绍一种新型超薄有机膜的制备技术以及该薄膜在光电器件方面的应用。报导了光敏管的制作工艺和其主要特性。     

朗谬尔（LB）热电薄膜及其在热电器件方面的应用

LB膜是一种由有机高分子定向排列组成的单分子层或多分子层薄膜材料。通过沉积两种不同种分子的交替层,可以形成非中心对称结构的热电性LB膜,是制作红外检测系统用热电元件的新型有机薄膜材料。本文主要叙述LB膜的制法、热电性膜的制法、热电性LB膜的进展概况及其在热电器件方面的应用和性能评价。     

Scattering Properties of Cylindrical Ferrite Posts and Their Applications

The scattering field of a ferrite post and a cylindrical ferrite post containing conducting post illuminated by a plane wave is analyzed. The special interest is the scattering property of the ferrite posts, which is resonating at certain modes such as TM₁₁ mode. We hope to know the speciality it shows and find its applications. It is found that the scattering field pattern of a resonating ferrite post is similar to the rotation of the scattering field pattern of a dielectric cylindrical post, which has the same dimension as ferrite. The scattering properties of the ferrite may give us some inspirations to explore its applications in microwave components. This property is utilized to explain the mechanism of the operation of the circulators. It also may be used in microstrip patch antenna, coupler and filter to control their properties. Other applications may be possible too. Some calculation results are presented.     

高分子磁性材料的频率、温度特性及应用

以二茂铁为原料合成的高分子磁性材料(OPM),其磁参数(μ',μ")基本不随使用频率及温度而变化,用它制作的电感、电容的电感量与电容量几乎与温度变化无关。比较了用OPM及NiZn—10制作的分路器及宽带变压器的性能,结果表明,在500~1 000 MHz频段,前者较后者的磁损耗约小1.0dB,而宽带放大器在200~300MHz的增益,前者较后者高5.0dB以上。