Magnetic Properties of Diluted Magnetic Nanowire

A magnetic diluted nanowire with cylindrical structure described by the Ising model is investigated. Using the effective field theory with a probability distribution technique, the influence of the dilution on the phase diagrams, susceptibility and the hysteresis loops are discussed in detail. Novel features are obtained for the thermal variations of longitudinal susceptibility and longitudinal magnetization. We have investigated the magnetic reversal of the system and have found the existence of triple hysteresis loops patterns, affected by the concentration of magnetic atoms, the temperature, and the exchange interaction between the core and the surface shell.     

Tweezing of Magnetic and Non‐Magnetic Objects with Magnetic Fields

Although strong magnetic fields cannot be conveniently “focused” like light, modern microfabrication techniques enable preparation of microstructures with which the field gradients – and resulting magnetic forces – can be localized to very small dimensions. This ability provides the foundation for magnetic tweezers which in their classical variant can address magnetic targets. More recently, the so‐called negative magnetophoretic tweezers have also been developed which enable trapping and manipulations of completely nonmagnetic particles provided that they are suspended in a high‐magnetic‐susceptibility liquid. These two modes of magnetic tweezing are complimentary techniques tailorable for different types of applications. This Progress Report provides the theoretical basis for both modalities and illustrates their specific uses ranging from the manipulation of colloids in 2D and 3D, to trapping of living cells, control of cell function, experiments with single molecules, and more.     

Magnetic Properties of Chalcopyrite-Based Diluted Magnetic Semiconductors

We calculated the chemical trends of transition metal-doped chalcopyrite DMS (diluted magnetic semiconductors) by the use of KKR–CPA–LDA method. The ferromagnetism was stable in V- and Cr-doped chalcopyrite DMS. In the case of Fe and Co doping, however, the spinglass-like state was realized. On the other hand, in the cases of Mn doped I-III-VI₂ and II-IV-V₂ type DMS, the ground state was ferromagnetic and spinglass-like, respectively.     

铁硅铝磁粉芯的磁特性研究

采用球磨制粉和模压成型方法制备了铁硅铝磁粉芯,并研究了其频率特性和直流叠加特性。结果表明,在测量的频率范围内（1～500kHz）,铁硅铝磁粉芯有效磁导率基本保持不变,而品质因数随频率的增加而增大,达到峰值后缓慢下降。在相同频率下,随着粉料粒度的减小,磁粉芯的有效磁导率降低,品质因数增加。铁硅铝磁粉芯具有良好的直流叠加特性,当直流偏磁场强度为1000e时,其有效磁导率变化率小于50％,且减小磁粉粒度可改善磁粉芯的直流叠加特性。     

磁制冷材料中一级磁相变的研究进展

磁制冷技术作为21世纪的新一代制冷技术已经受到了关注。因此近年来具有一级磁相变的磁制冷材料成为全球学术界的一个研究热点,并越来越受到工业界的重视。主要介绍了磁制冷材料中的一级磁相变特点,综述了具有一级磁相变的磁制冷材料的研究进展和应用现状。最后展望了具有一级磁相变的磁制冷材料的发展趋势。     

Magnetic Nanocapsules

A brief review on recent advances in the area of the magnetic nanocapsules is given. The most applicable nanoencapsulation procedures are introduced, which include： （1） physical techniques such as arc-discharge, evaporating, etc.; （2） chemical techniques such as chemical vapor deposition, solid-state reactions, etc. The structure and magnetic properties of various nanocapsules with different core/shell structures are studied in details, for possibly applications in magnetic recording, magnetic refrigerator, magnetic fluids, superconductors and medicine.     

Magnetic Multilayers

Magnetic multilayers are artificially structured materials made of ultrathin films of two different mate-rials,alternately ferromagnetic and non-ferromagnetic.They exhibit new magnetic properties differ-ent from those of bulk materials.We review the magnetic properties of metallic magnetic multilayersand focus on interface magnetic anisotropy,giant magnetoresistance and interlayer couplings,whichare of great promise for applications to high density magnetic storage.     

磁制冷器

磁制冷是一种以磁热效应为基础的制冷方法.最早是由德国物理学家于1880年发现。早期用于制取极低的温度。近年来,室温磁制冷取得了较大的突破,已经研制出适合家用的磁制冷冰箱,同时由于它的制冷系数高和对大气的全球气候变暖影响小等优点,将成为一种很有发展前途的制冷方式。本文论述磁制冷和磁制冷冰箱的基本原理。     

SQUID-Detected Magnetic Resonance Imaging in Microtesla Magnetic Fields

We describe studies of nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI) of liquid samples at room temperature in microtesla magnetic fields. The nuclear spins are prepolarized in a strong transient field. The magnetic signals generated by the precessing spins, which range in frequency from tens of Hz to several kHz, are detected by a low-transition temperature dc SQUID (Superconducting QUantum Interference Device) coupled to an untuned, superconducting flux transformer configured as an axial gradiometer. The combination of prepolarization and frequency-independent detector sensitivity results in a high signal-to-noise ratio and high spectral resolution (～1 Hz) even in grossly inhomogeneous magnetic fields. In the NMR experiments, the high spectral resolution enables us to detect the 10-Hz splitting of the spectrum of protons due to their scalar coupling to a ³¹P nucleus. Furthermore, the broadband detection scheme combined with a non-resonant field-reversal spin echo allows the simultaneous observation of signals from protons and ³¹P nuclei, even though their NMR resonance frequencies differ by a factor of 2.5. We extend our methodology to MRI in microtesla fields, where the high spectral resolution translates into high spatial resolution. We demonstrate two-dimensional images of a mineral oil phantom and slices of peppers, with a spatial resolution of about 1 mm. We also image an intact pepper using slice selection, again with 1-mm resolution. In further experiments we demonstrate T₁-contrast imaging of a water phantom, some parts of which were doped with a paramagnetic salt to reduce the longitudinal relaxation time T₁. Possible applications of this MRI technique include screening for tumors and integration with existing multichannel SQUID systems for brain imaging.     

基于SQUID的磁纳米粒子磁特性测量研究

基于超导量子干涉器件(SQUID)的高灵敏磁通电压转换特性,将探测磁纳米粒子磁特性的线圈的微弱磁信号转换成电压信号输出。设计了包含激励源模块,信号测量模块,人机交互模块的测量系统,并采用标定线圈完成了测量系统的标定,实测数据表明,该系统可用于对磁纳米粒子磁特性的测量,为后续研究适用于生物体内温度测量的方法提供了支持。     

磁编码器多极磁鼓材料的研究

通过分析磁编码器磁鼓的结构和制作工艺，研究采用粘结磁性材料做磁编码器用磁鼓材料。粘结磁体采用硅烷为偶联剂，环氧树脂为粘合剂。研究了不同组份的配方对磁鼓材料的影响。制备出了Ｂｒ＝１２７７Ｇｓ，Ｈｃ＝１０７９Ｏｅ，（ＢＨ）ｍａｘ＝０．５３ＭＧＯｅ的磁鼓材料。     

热疗用磁性材料研究进展

在介绍热疗用磁性材料研究概况的基础上,对其研究进展进行了详细综述,重点介绍了Fe3O4和γ-Fe2O3两类材料的制备方法、产热能力研究以及动物实验等方面的内容,最后对热疗用磁性材料的发展前景进行了展望.     

磁旋转编码器多极磁鼓的研制

在分析磁骗码器的原理和结构的基础上，采用粘结磁体作磁编码器多极磁鼓记录介质材料，运用体成型工艺，研制出了多种型号的磁鼓。同时对磁鼓进行了充磁和气隙磁性能分析。     

磁悬浮运动平台的磁场分析及优化设计

研制了一种新型磁悬浮平台,该平台定子采用无铁心式的克莱姆绕组,消除了固有齿槽效应,动子采用Halbach 磁阵列结构方式,由于平台输出推力与悬浮的稳定性主要与其气隙磁场的分布情况有直接关系,因此提高气隙磁场的正弦分布是改善其工作特性的难点和重点. 为了改善气隙磁场的分布问题,提出了一个优化磁场分布的目标函数,并采用步长加速法对平台磁场进行了优化设计,大大降低了磁场谐波分量,改善了气隙磁场分布状态. 将优化结果运用到实际的平台中,对该运动平台进行了阶跃响应实验,实验结果表明满足平台需要达到纳米级精度的要求.     

磁性Fe3O4纳米颗粒的制备和磁性研究

讨论了一种制备磁性Fe3O4纳米颗粒的新方法，利用自行设计的反应容器，引入磁场和电场的相互作用，制得颗粒大小比较均一、分散性较好的Fe3O4纳米颗粒。通过改变反应时间、磁铁高度，得到了平均粒径为5～10nm的Fe3O4纳米颗粒，并对其进行磁特性测量。     

Comparison of Magnetic Field Analysis Methods Considering Magnetic Anisotropy

The magnetic field analysis results on grain-oriented silicon steel sheet and nongrain-oriented silicon steel sheet by the isotropic method, the two-axis isotropic method, the two-axis anisotropic method, the $varphi$ anisotropic method, and the $theta_{rm HB}$ anisotropic method, which are 2-D magnetic analysis methods, are compared. In analyzing the magnetic field in the isotropic material, the isotropic method is more appropriate than the two-axis isotropic method. For the anisotropic material in which the magnetic flux density is much less than saturation magnetic flux density, the two-axis anisotropic method is more preferable than the $varphi$ anisotropic method, because the result of the two-axis anisotropic method is similar to that of the $theta_{rm HB}$ anisotropic method. However, for the analysis in high magnetic flux density near the saturation magnetic flux density, the $varphi$ anisotropic method is more suitable than the two-axis anisotropic method.