一种新型油田堵水剂的制备

以自制Fe3O4磁粉、微晶纤维素与淀粉、丙烯酸,交联剂为主要原料合成了磁性高吸水性树脂。探讨了Fe3+、Fe2+加入速度对Fe3O4磁粉的影响以及Fe3O4磁粉加入对磁性高吸水性树脂的饱和磁化强度、吸水率的影响。结果表明,Fe3+、Fe2+加入速度过快,Fe3O4磁粉磁性降低。实验测得磁性高分子吸水树脂的饱和磁化强度为0.7 Am2/kg、吸水率为60 g/g,能够应用于油田堵水领域中。     

二灰稳定磁化轮道路基层在迁安市的推广应用

通过对二灰稳定磁化轮和二灰稳定碎石配合比设计中强度的比较以及用二灰稳定磁化轮做道路基层的试验,分析了二灰稳定磁化轮道路基层的经济效益和社会效益,阐述了磁化轮在工程建设中广阔的应用前景。     

饱和铁心型超导限流器满足电网重合闸条件分析

饱和铁心型超导限流器(saturated iron-coresuperconducting fault current limiter,SI-SFCL)在限流过程中独特的非线性阻抗变化特性与电网继电保护的配合是一项关键技术,尤其是限流器在完成限流后需要快速恢复,以配合电网断路器重合闸的要求。限流器的恢复过程本质上是超导磁体的重新励磁,既要在尽量短的时间内完成超导磁体的充磁,又要尽量降低快速励磁时对励磁电压、电流的要求,降低直流励磁系统的设计难度,并提高设备运行的安全性和稳定性。基于对上述超导限流器重合闸要素的分析,得出结论:SI-SFCL在电网重合闸时,直流励磁不必完全恢复至额定工作值,只要能够确保在一定交流退磁作用下,铁心的最小磁化强度处于磁化曲线的拐点处即可。用PSIM进行仿真分析,校验了该判据的合理性。     

纳米磁性Mn3O4粉末的溶剂热法合成及表征

以MnO2为主要原料,应用溶剂热法合成了纳米磁性Mn3O4粉体.研究和讨论了反应温度、填充度、溶剂种类、降温速率对产物性能的影响,得到溶剂热法制备纳米磁性Mn3O4的最佳条件.产物经XRD表征为单一相Mn3O4,经粒度分析仪及透射电镜(TEM)检测,为四方晶型,平均粒径为55nm.     

Magnetic Properties of Al-Doped Na0.7Co1-xAlxO2

Single phase polycrystalline samples Na0.7Co1-xAlxO2 (x=0, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30) were prepared by solid state reaction. The magnetic properties from 5 K to 300 K have been studied by dc and ac magnetic susceptibility measurements. Samples with lower doping quantity (x=0, 0.05, 0.10) showed paramagnetic behaviors, but those with higher doping quantity (x=0.20, 0.25, 0.30) showed spin-glass behaviors with a freezing temperature (Tf) of about 13 K.     

Review on recent advances of zinc substituted cobalt ferrite nanoparticles: Synthesis characterization and diverse applications

Researchers have taken a prodigious consideration in characterizing and synthesizing zinc substituted cobalt ferrite nanoparticles because of their substantial applications across diverse technological and industrial fields. Zinc substituted cobalt ferrite nanoparticles are a class of lenient magnetic nanomaterials, which have potentially high magnetic, optical, electrical, and dielectric properties. These properties include a high value of permeability, low power losses, permittivity, saturation magnetization, coercivity, resistivity, and other beneficial properties that make them promise candidates for applications in various fields. These ferrites are also used in biomedical areas such as MRI and cancer treatments. In electronic fields, zinc substituted cobalt ferrite nanoparticles are used to make transducers, transformers, biosensors, and sensors. Apart from these advantages, they are found in our everyday electronic and electrical appliances like LED bulb, refrigerator, mobile charger, TV, microwave oven, juicer, washing machine, mixer, iron, printer, laptop, mobile, desktop, etc. Hence, the current review reports some properties of these spinel ferrites and emphasizes the different synthesis techniques that can be used to prepare them. Afterward, the impact of dopant on the materials' properties, the characterization techniques, and the momentous application in the present era have been well discussed.     

Negative magnetization and exchange bias effect in Fe-doped CoCr2O4

Polycrystalline ceramics of Co(Cr_1-xFe_x)₂O₄ (0?≤?x?≤?0.12) were experimentally studied based on a series of temperature and time-dependent dc magnetic measurements using different magnetic field histories. Magnetization in field cooling process was continuously decreased for doping content x in the range of 0?≤?x?≤?0.04. Remarkable negative magnetization is observed when x reaches to 0.06 and persists up to x?=?0.1. Two-sublattice model is established and competition of the two magnetic sublattices is responsible for the phenomenon. The magnetic switching effect is realized just by changing the magnitude of the applied magnetic field and double magnetocaloric effects are obtained. These unique features under low magnetic fields show attractive for application in spintronic devices due to that the magnetic state can effectively be tuned through magnetic field or temperature. Besides, the system exhibits both positive and negative exchange bias fields which are considered to be originating from the unidirectional anisotropy of exchange coupling of antiferromagnetic/ferromagnetic phases and spin reorientation of the two sublattices magnetic moments, respectively.     

The microstructure and magnetic properties of Ca2+ ion doped GdCrO3

In this paper, the crystal structure, vacancy defect, local electron density and magnetic properties of Gd_1-xCa_xCrO₃ (0 ≤ x ≤ 0.3) polycrystalline samples were investigated systematically. The crystal structural analyses show that all the samples are orthorhombic phase and a structural distortion happens around x = 0.3. Due to the formation of Cr⁴⁺ ions, both the lattice constant and the Cr–O bond length decrease. The results of positron annihilation spectrum reveals that the vacancy defect concentration increases and the local electron structure changes with the introduction of Ca²⁺ ions. The field-cooled (FC) and zero-field cooled (ZFC) curves of Gd_1-xCa_xCrO₃ samples measured under H = 100 Oe exhibits negative magnetization characteristics due to the interaction between Gd³⁺ and Cr³⁺ ions, and the magnetism can be affected by the structural distortion.     

Ultrafast Orbital‐Oriented Control of Magnetization in Half‐Metallic La0.7Sr0.3MnO3 Films

Manipulating spins by ultrafast pulse laser provides a new avenue to switch the magnetization for spintronic applications. While the spin–orbit coupling is known to play a pivotal role in the ultrafast laser‐induced demagnetization, the effect of the anisotropic spin–orbit coupling on the transient magnetization remains an open issue. This study uncovers the role of anisotropic spin–orbit coupling in the spin dynamics in a half‐metallic La_0.7Sr_0.3MnO₃ film by ultrafast pump–probe technique. The magnetic order is found to be transiently enhanced or attenuated within the initial sub‐picosecond when the probe light is tuned to be s‐ or p‐polarized, respectively. The subsequent slow demagnetization amplitude follows the fourfold symmetry of the ${\mathrm{d}}_{x^2?y^2}$ orbitals as a function of the polarization angles of the probe light. A model based on the Elliott–Yafet spin‐flip scatterings is proposed to reveal that the transient magnetization enhancement is related to the spin‐mixed states arising from the anisotropic spin–orbit coupling. The findings provide new insights into the spin dynamics in magnetic systems with anisotropic spin–orbit coupling as well as perspectives for the ultrafast control of information process in spintronic devices.     

An Artificial Skyrmion Platform with Robust Tunability in Synthetic Antiferromagnetic Multilayers

Magnetic skyrmions are topologically nontrivial spin structures, and their existence in ferromagnetically coupled multilayers has been widely reported with a disordered arrangement. Here, a nucleation scenario of ordered skyrmions in nanostructured synthetic antiferromagnetic (SAF) multilayers is proposed and experimentally demonstrated using direct magnetization imaging, indirect magnetometer and magnetoresistance measurement, and micromagnetic simulation. Instead of relying on Dzyaloshinskii–Moriya interaction, the antiferromagnetic interlayer exchange coupling in the SAF multilayers fulfills the role of nucleation and stabilization of skyrmions. The robustness of the proposed skyrmion nucleation scenario is examined against temperature from 4.5 to 300 K and device size from 400 to 1200 nm. Interestingly, these synthetic skyrmions still behave well with a size less than 100 nm. The higher stability than generic magnetic domains can be attributed to topological protection. The results thus provide an artificial skyrmion platform to meet the functional needs of high density and designable arrangement in magnonic and spintronic applications.