机器油液中磨粒铁磁性甄别及检测系统研究

针对油液磨粒分析中磨粒铁磁性甄别的要求,设计了磨粒分离传感器和视觉检测系统。对磨粒在流场和磁场中受力进行了分析,提出了根据总流道和非铁磁性磨粒流动的检测信息,对铁磁性磨粒间接检测的方法。运用DPIV的方法对观测点的流场进行检测,解决了根据单幅图像准确计算磨粒的污染度的问题。最后,对系统的检测性能进行了实验验证。     

基于磁阻传感器的铁磁体探测系统设计

简要介绍了铁磁体在地磁场中的模型,针对磁异信号的检测,设计了一种基于各项异性磁阻传感器的三轴测试系统。硬件电路主要包括：磁阻传感器、置位／复位电路、信号调理电路、A／D转换电路及控制电路。该系统由Honeywell公司HMC1001和1002组成三轴测量传感器,利用FPGA作为控制器实现对磁异信号的采集。试验结果表明,系统能够对移动目标铁磁体进行有效检测,并可达到较高的检测精度。     

纳米材料铁磁性研究

在分子场理论中,假定一个系统由一个单态的基态和一个三重态的激发态组成,该系统中激发态的能量比基态高Δ。通过理论计算得到该系统的磁矩公式。并且在紧束缚模型框架下,得到铁磁纳米材料的磁化率解析解。     

Chemically Exfoliated VSe2 Monolayers with Room‐Temperature Ferromagnetism

Among van der Waals layered ferromagnets, monolayer vanadium diselenide (VSe₂) stands out due to its robust ferromagnetism. However, the exfoliation of monolayer VSe₂ is challenging, not least because the monolayer flake is extremely unstable in air. Using an electrochemical exfoliation approach with organic cations as the intercalants, monolayer 1T‐VSe₂ flakes are successfully obtained from the bulk crystal at high yield. Thiol molecules are further introduced onto the VSe₂ surface to passivate the exfoliated flakes, which improves the air stability of the flakes for subsequent characterizations. Room‐temperature ferromagnetism is confirmed on the exfoliated 2D VSe₂ flakes using a superconducting quantum interference device (SQUID), X‐ray magnetic circular dichroism (XMCD), and magnetic force microscopy (MFM), where the monolayer flake displays the strongest ferromagnetic properties. Se vacancies, which can be ubiquitous in such materials, also contribute to the ferromagnetism of VSe₂, although density functional theory (DFT) calculations show that such effect can be minimized by physisorbed oxygen molecules or covalently bound thiol molecules.     

溶胶-凝胶法制备的Zn_(1-x)Co_xO晶体粉末的结构和磁性行为

利用溶胶凝胶法制备了Zn_(1-x)Co_xO(x=0.01-0.05,原子分数)纳米晶体粉末,利用XRD,TEM和SEM对其结构、结晶状态、形貌和成分进行了表征和分析.结果表明,所有样品均由尺寸约为100 nm的晶体颗粒组成,Zn_(1-x)Co_xO的晶格常数均比未掺杂的ZnO晶格常数小,且保持了单一纤锌矿ZnO结构,实际掺杂浓度与名义掺杂浓度基本匹配.振动样品磁强计测试结果显示,所有样品都具有室温铁磁性.结合微结构,确定该铁磁性为材料的本征属性,并推断O空位是铁磁交换作用的媒介,晶粒度的大小也影响了样品的磁性行为.     

Effect of the nanostructure on room temperature ferromagnetism and resistivity of undoped ZnO thin films grown by chemical vapor deposition

Undoped zinc oxide thin films having various types of morphology and nanostructure were deposited by metal organic chemical vapor deposition (MOCVD) on single-crystalline substrates. Water-assisted MOCVD process at low temperatures (300-500 °C) was applied along with conventional MOCVD in oxygen-containing atmosphere at 500 and 600 °C. The strong correlation between room-temperature ferromagnetism of the films, their electrical properties and morphology at nano-scale was demonstrated.     

Mechanism-based tuning of room-temperature ferromagnetism in Mn-doped β-Ga2O3 by annealing atmosphere

Mn-doped β-Ga₂O₃ (GMO) films with room-temperature ferromagnetism (RTFM) are synthesized by polymer-assisted deposition, and the effects of annealing atmosphere (air or pure O₂ gas) on their structures and physical properties are investigated. The characterizations show that the concentrations of vacancy defects and Mn dopants in various valence states and lattice constants of the samples are all modulated by the annealing atmosphere. Notably, the samples annealed in air (GMO–air) exhibit a saturation magnetization as strong as 170% times that of the samples annealed in pure O₂ gas (GMO–O₂), which can be quantitatively explained by oxygen vacancy (V_O)-controlled ferromagnetism due to bound magnetic polarons established between delocalized hydrogenic electrons of V_Os and local magnetic moments of Mn²⁺, Mn³⁺, and Mn⁴⁺ ions in the samples. Our results provide insights into mechanism-based tuning of RTFM in Ga₂O₃ and may be useful for design, fabrication, and application of related spintronic materials.     

γ-irradiation hardness investigations of (PANI)1−x(Bi2Te3)x composites for thermistor applications

The (PANI)_1−x(Bi₂Te₃)_x composites were successfully synthesized. These composites have a simple physical combination of intrinsic conducting polymer and nanocrystal topological insulator materials which are promising new materials for unusual applications. The influence of γ-irradiation (100 kGy doses) on the performance of the (PANI)_1−x(Bi₂Te₃)_x composites was described by atypical techniques to assess the radiation hardness of the samples. X-ray diffraction and Raman spectroscopy measurements show the semi-crystalline phases, the other structural parameters, and the phonon modes. The compositional analysis and the morphological properties were investigated by energy-dispersive X-ray, while transmission electron microscopy imaging confirmed the morphology of the dopants of Bi₂Te₃ nanoparticles into the polyaniline (PANI) matrix, which shows the accumulation of the particles. Thermogravimetric analysis figured out the degradation behavior of the compositions. The representative electron spin resonance (ESR) signal exhibits a narrow single-line ESR spectrum for PANI/Bi₂Te₃ nanoparticle concentrations. (PANI)_1−x(Bi₂Te₃)_x illustrates unexpected ferromagnetic behavior that confirms the magnetic performance of the samples without introducing any magnetic dopants. The obtained materials showed promising performance for using such hybrid materials as a positive temperature coefficient thermistor.     

Electromagnetic Functionalization of Wide‐Bandgap Dielectric Oxides by Boron Interstitial Doping

A surge in interest of oxide‐based materials is testimony for their potential utility in a wide array of device applications and offers a fascinating landscape for tuning the functional properties through a variety of physical and chemical parameters. In particular, selective electronic/defect doping has been demonstrated to be vital in tailoring novel functionalities, not existing in the bulk host oxides. Here, an extraordinary interstitial doping effect is demonstrated centered around a light element, boron (B). The host matrix is a novel composite system, made from discrete bulk LaAlO₃:LaBO₃ compounds. The findings show a spontaneous ordering of the interstitial B cations within the host LaAlO₃ lattices, and subsequent spin‐polarized charge injection into the neighboring cations. This leads to a series of remarkable cation‐dominated electrical switching and high‐temperature ferromagnetism. Hence, the induced interstitial doping serves to transform a nonmagnetic insulating bulk oxide into a ferromagnetic ionic–electronic conductor. This unique interstitial B doping effect upon its control is proposed to be as a general route for extracting/modifying multifunctional properties in bulk oxides utilized in energy and spin‐based applications.