Room-temperature multiferroic characteristics and unique vortex domain structures of h-Yb1−xInxFeO3 solid solutions

Hexagonal rare-earth ferrites (h-RFeO₃) have attracted much scientific attention due to their room-temperature multiferroicity. However, it is still a hard job to obtain h-RFeO₃ bulk materials because of the meta-stability of such hexagonal phase, and the evaluation of room-temperature ferroelectric and magnetoelectric characteristics in such materials is also a challengeable issue. In the present work, Yb_1−xIn_xFeO₃ ceramics with the stable hexagonal structure were obtained by introducing chemical pressure, where the unique ferroelectric domain structures of sixfold vortex combined with tenfold vortex with a typical size of ~400 nm were determined. Symmetry of the present system evolved from centrosymmetric orthorhombic Pbnm (x = 0–0.4) to non-centrosymmetric hexagonal P6₃cm (x = 0.5 and 0.6) with a ferroelectric polarization up to 3.2 μC/cm², and finally to centrosymmetric hexagonal P6₃/mmc (x = 0.7 and 0.8). The Curie point decreased monotonically from 723 K to a temperature below room temperature with increasing x, and the antiferromagnetic phase transition above room temperature was determined for all compositions. Meanwhile, a large linear magnetoelectric coefficient (α_ME) up to 0.96 mV/cm Oe was obtained at room temperature, and this indicated the great application potential for magnetoelectric devices.     

管道周向励磁漏磁检测磁路设计

管道周向励磁漏磁检测技术是一种新的检测方法,对于检测和定量评定轴向导向缺陷具有潜在优势。磁化器磁路设计是漏磁检测需要解决的首要问题,采用磁路计算原理研究管道磁化磁路中永磁体长度、厚度和宽度改变时,管道表面缺陷产生的漏磁场的变化情况,得到了缺陷漏磁场随永磁体长度、厚度和宽度改变时的变化规律。此规律有助于从整体上把握永磁体磁路设计,改善磁化效果,提高漏磁检测灵敏度,进而为漏磁检测磁路的设计提供依据。     

磁化对水的性质影响的研究

研究了磁化前后和磁场强度、磁化时间对蒸馏水、自来水、工业废水的红外光谱、表面张力、电导率和pH值的影响,结果表明:磁化前后的红外光谱无明显变化,水的电导率,表面张力,pH值等呈现明显的周期性变化,且变化情况与磁场强度和磁化时间有关,并发现磁化水的电导率有滞后效应。对磁化水性能变化的机理提出了初步见解。     

磁化复混肥料的磁化工艺及磁性稳定性研究

实验室条件下以粉煤灰、钢渣粉、选铁尾矿粉为磁性材料,研究了磁性材料的磁化性能、生产磁化复混肥的磁化工艺及肥料磁性的稳定性,并测定了磁化复混肥料的重金属含量。结果表明,磁化工艺以先造粒后磁化为佳;以选铁尾矿粉为磁性材料,在磁化场强为8 000 mT下磁化10 s生产的磁化复混肥料磁化效果最佳,且放置时间对肥料的磁感应强度影响弱;以三种磁性材料制成的磁化复混肥料的重金属含量均低于国家标准,使用安全。     

A study on the structural,optical, magnetization reversal and bipolar magnetic switching behavior of SmCr0.85Mn0.15O3 nanoparticles

SmCr_0.85Mn_0.15O₃ (SCMO) nanoparticles with Pnma space group have been synthesized by the sol-gel auto-combustion method with an average crystallite size of 70 nm. The structural analysis indicates a comparable unit cell volume with that of the bulk compound. The structural distortion is calculated by various factors such as cell distortion factor, octahedral distortion, dodecahedral distortion, strain and tolerance factor, which arise due to the Jahn-Teller (JT) effect and a tilting in the octahedra. The obtained distortion values suggest a larger distortion in the structure due to the nano-size effect compared with the bulk counterpart. The diffuse reflectance spectrum confirms the semiconducting nature of SCMO nanoparticles with an optical bandgap of 2.9 eV, higher than that of the bulk compound. The extinction coefficient of the SCMO nanoparticles exhibits a larger value than that of the bulk, suggesting a higher absorbing character of the nanoparticles. The temperature-dependent magnetization reveals a decrease in the Néel temperature on Mn substitution. The negative magnetization is also observed below the compensation temperature, T_comp. Moreover, a stable magnetic switching behavior is demonstrated by varying temperatures under ZFC and FC protocols. The semiconducting nature and the stable magnetic switching behavior of SCMO nanoparticles make them suitable for optoelectronic, photovoltaic, and magnetic switching applications.     

SrRuO_3的制备及其结构与磁性

利用固相反应法制备了多晶SrRuO3固体。利用X射线衍射确定样品的相结构为正交畸变钙钛矿结构,空间群为Pbnm。利用最小二乘法求得晶格常数为a=0.5548nm,b=0.5551nm,c=0.7830nm。利用物理性质测量系统(PPMS)测量样品在不同偏磁场下的交流磁化率、零场冷却(ZFC)和加场冷却(FC)磁化强度随温度的变化规律,对此规律给出了合理解释。     

磁屏蔽效应对磁场除垢防垢效果的影响

在磁场除垢防垢应用中,管道材料性质的差异会导致流体介质内部的真实磁场大小与理论值存在一定偏差,即磁屏蔽现象,这会大大影响磁处理效果。因此,采用对照试验方法建立两套装置,研究螺线管缠绕段材料分别为铁管和塑料管时,磁屏蔽效应对磁处理效果的影响。试验结果表明,减小磁屏蔽效应,电子除垢仪的除垢、防垢及缓蚀效果得到了提升。     

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。     

纳米磁性流体的制备及性能分析

在磁流体制备过程中,利用x衍射仪(xRD)和透射电镜(TEM)对磁性纳米微粒的组成及粒径进行了分析,研究了磁性纳米微粒和表面活性剂对磁流体性能的影响.实验表明:Fe2 :Fe3 =1:2,反应温度为160℃,反应时间为6h,在适宜的时间加入6%的表面活性剂可以制备出性能较好的磁性流体.     

磁化技术在工业水处理中的应用

磁化技术是一门新兴的科学技术,将磁化技术应用于工业水的处理,是近年来的热门研究课题。本文在介绍了磁化分离技术的原理及分类、磁化水的性质和磁化分离特点的基础上,对近年来所研究开发的磁化处理工业水技术及其应用作了较为详细的介绍与评述。     

Hexagonal SrFe12O19 ferrite with high saturation magnetization

Hexagonal M-type ferrites with a nominal composition SrFe₁₂O₁₉ (SrM) were prepared via a ceramic route using acicular goethite (α-FeOOH) nanopowders obtained at different hydrothermal temperature as one of the starting materials, and their structural and magnetic properties were investigated. The best hydrothermal temperature of α-FeOOH used was found to be 1ower than 180?°C, and the best sintering temperature of SrM should be 1200?°C. The highest saturation magnetization of SrM reaches 76.7?emu/g, a very high value rarely found in the SrM ferrites without any substitution or dopant.     

平行磁场作用下电沉积Co-Ni-Mn-P磁性薄膜

在平行磁场作用下电沉积Co-Ni-Mn-P磁性薄膜。研究了平行磁场对电沉积过程及薄膜性能的影响。研究发现:施加平行磁场,有利于提高离子的传质速率,从而提高沉积效率。平行磁场作用下电沉积制备的Co-Ni-Mn-P磁性薄膜呈现出"枝晶状"结构,矫顽力和比饱和磁化强度更高。     

Effect of Nickel–Cobalt–Zinc Ferrite Filler on Magnetic and Thermal Properties of Thermoplastic Natural Rubber Composites

A sample of Ni_0.25Co_0.25Zn_0.5Fe₂O₄ ferrite was prepared by a double-staged sintering method in air. Thermoplastic natural rubber (TPNR) was prepared by melt blending of natural rubber (NR), liquid natural rubber (LNR), and high density polyethylene (HDPE) in an internal mixer Brabender Plasticorder PL 2000. Magnetic polymer composites were prepared from the ferrite and TPNR matrix using the same melt blending method at 135°C with mixing rate of 50 r.p.m. for 12 min. The fillers were varied from 5 to 30 weight percent. A uniform dispersion of the filler in the matrix was confirmed by thermogravimetric analysis (TGA). The density of the composites was determined using densitometer MD 200S. Magnetic properties were studied using a vibrating sample magnetometer (VSM) at room temperature (25°C). The results show that magnetization (M), saturation magnetization (M_S), remanent magnetization (M_R), initial susceptibility (χ_i) and initial permeability (μ_i) increase with increasing filler content at all compositions. The composites can be classified as soft magnetic materials as their coercivities are in the range of 30–36 Oe. The differential scanning calorimetric (DSC) results indicate that the glass transition temperature (T_g) and the melting point (T_m) of all the composites are independent of the filler content. The thermal conductivity of the composites was found to be in the range of 0.26 to 0.52 W m^?1 K^?1.     

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.     

高能球磨法制备纳米Fe3O4磁性颗粒的结构性能研究

采用高能球磨法制备Fe3 O4纳米磁性颗粒,用XRD、VSM、SEM等方法对样品进行表征并用四端法对样品的电导率进行测量,然后对样品的结构性能作定性和定量分析.结果表明:随着研磨时间增加,Fe3O4晶粒的衍射峰变宽,衍射峰强度减弱,同时有少量α-Fe2 O3生成;晶格的显微应变增加;Fe3 O4磁性颗粒的饱和磁化强度降低,矫顽力先变大后减小;对压片后样品的电导率进行测试,发现电导率降低;随着研磨时间增加,晶粒会出现团聚现象,形成粒径更大的二次颗粒,为防止该现象,研磨时间应控制在110 h左右.