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磁性薄膜磁学特性电场调控的相关研究对开发新型低功耗磁信息器件具有突出意义.本文基于电场调控磁性的基本理论,以OOMMF(Object Oriented Micro-Magnetic Frame)微磁学仿真软件为工具,研究了电场对生长于PZN-PT单晶衬底上Fe_3O_4单晶薄膜磁学特性的调控.研究结果显示:无外加电场时,薄膜表现出典型的软磁特性;沿衬底[001]方向施加的外加电场可以使得薄膜矫顽力、矩形比等磁学特性发生显著改变:当外加磁场沿[100]([010])时,施加正值(负值)电场强度可以显著增大薄膜的矫顽力与矩形比,当电场强度不小于0.6 MV/m时薄膜矩形比达到1.这是因为外加电场导致薄膜产生单轴应力各向异性,使得薄膜的等效磁各向异性发生了从无外电场下的面内四重磁晶各向异性向高电场下的近似单轴磁各向异性的过渡.外加1 MV/m与-1 MV/m的电场时等效易磁化轴分别沿[100]与[010]方向.另外,外加1 MV/m(-1 MV/m)的电场强度可以使得铁磁共振的频率增大(减小)接近1 GHz. 相似文献
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Effects of notches on the order of flux-closure state formation in bi-rings by micromagnetic simulation 下载免费PDF全文
The effects of the number and the location of notches on the formation of flux-closure states in bi-rings with fields applied in the x direction (i.e., along the short axis direction of bi-rings) and y direction (i.e., along the long axis direction of bi-rings) are investigated using micromagnetic simulation. For the bi-rings with one notch and the bi-rings with two notches symmetric about y axis, the order of flux-closure state formation in each ring can be controlled. But the flux-closure state forms simultaneously in each ring for the bi-rings with two notches symmetric about x axis. For the bi-rings with two notches that are symmetric neither about x axis nor about y axis, only one ring can form a flux-closure state in the y-direction field and no flux-closure state can be found in rings in the x-direction field. Therefore, logic states can be defined by controlling the order of flux-closure state formation, which can be utilized in future logic devices. 相似文献
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采用共沉淀法和溶剂热法制备了不同尺寸的Fe_3O_4纳米粒子,通过Stber法和溶胶-凝胶法在Fe_3O_4磁核上包覆SiO_2和Ti O2壳层获得不同尺寸的Fe_3O_4@SiO_2@Ti O2复合纳米结构.采用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)和振动样品磁强计(VSM)等对其结构、形貌和磁性进行了研究.结果表明,大尺寸复合纳米粒子包覆均匀,分散性好,饱和磁化强度较大,有利于TiO_2光催化剂的磁回收与再利用. 相似文献
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采用共沉淀法和溶剂热法制备了不同尺寸的Fe3O4纳米粒子,通过Stöber法和溶胶-凝胶法在Fe3O4磁核上包覆SiO2和TiO2壳层获得不同尺寸的Fe3O4@SiO2@TiO2复合纳米结构.采用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)和振动样品磁强计(VSM)等对其结构、形貌和磁性进行了研究.结果表明,大尺寸复合纳米粒子包覆均匀,分散性好,饱和磁化强度较大,有利于TiO2光催化剂的磁回收与再利用. 相似文献
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搭建了电爆炸金属丝实验平台,在空气中电爆炸铁丝来制备纳米金属颗粒。利用电阻分压器与Rogowski线圈来测量电爆炸过程中铁丝上的负载电压与电流。将负载电压与电流之积进行时间积分来估算沉积在铁丝上的能量。使用光电探测器对电爆炸过程中产生的等离子体发光信号进行探测。对铁丝电爆炸后形成的产物使用高倍显微镜、扫描电镜(SEM)、透射电镜(TEM)、能谱分析仪(EDS)以及X射线衍射仪(XRD)进行观测,来研究其物相特性。实验结果表明:电爆炸过程中,当铁丝由液相变为气相时,其电阻急剧增加,因此电流几乎不能流过铁丝,同时铁丝上的负载电压会趋近于电容器的初始充电电压。随着能量的持续积累,等离子体在爆炸腔中形成。由于原本被阻断的电流能够从低电阻等离子体中流过,因此电压电流波形变为欠阻尼波形。电爆炸铁丝所得的产物为Fe3O4纳米颗粒,其中大部分呈规则的球形。Fe3O4纳米颗粒的粒径主要分布在30~60 nm之间,并且符合对数正态分布。 相似文献
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磁性纳米颗粒Fe3O4固定化纤维素酶的光谱学研究 总被引:1,自引:0,他引:1
以氨水作沉淀剂,用共沉淀法制备了磁性纳米颗粒Fe3O4,并以此为载体,通过碳化二亚胺的活化作用将纤维素酶固定化,通过傅里叶红外和重复多次催化实验证实纤维素酶在磁性纳米颗粒上的固定,透射电镜表征了固定化酶微粒的形貌.用DNS分光光度法测定固定化纤维素酶的活性,研究表明磁性固定化酶的催化作用的最适温度为60℃和pH值为3.94~5.50.结果表明,磁性固定化纤维素酶具有比自由酶更好的热稳定性,贮存稳定性和更广泛的pH值适用范围,为纤维素的转化和利用效率的提高提供了理论基础. 相似文献
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The electron‐density distribution and the contribution to anomalous scattering factors for Fe ions in magnetite have been analyzed by X‐ray resonant scattering at the pre‐edge of Fe K absorption. Synchrotron X‐ray experiments were carried out using a conventional four‐circle diffractometer in the right‐handed circular polarization. Difference‐Fourier synthesis was applied with a difference in structure factors measured on and off the pre‐edge (Eon = 7.1082 keV, Eoff = 7.1051 keV). Electron‐density peaks due to X‐ray resonant scattering were clearly observed for both A and B sites. The real part of the anomalous scattering factor f′ has been determined site‐independently, based on the crystal‐structure refinements, to minimize the squared residuals at the Fe K pre‐edge. The f′ values obtained at Eon and Eoff are ?7.063 and ?6.682 for the A site and ?6.971 and ?6.709 for the B site, which are significantly smaller than the values of ?6.206 and ?5.844, respectively, estimated from the Kramers–Kronig transform. The f′ values at Eon are reasonably smaller than those at Eoff. Our results using a symmetry‐based consideration suggest that the origin of the pre‐edge peak is Fe ions occupying both A and B sites, where p–d mixing is needed with hybridized electrons of Fe in both sites overlapping the neighbouring O atoms. 相似文献
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提出了一种以Fe3O4纳米颗粒和聚二甲基硅氧烷(PDMS)组成的复合材料为介质的平行板磁电容结构,并对其产生的磁电容效应的特点以及影响磁电容效应的因素进行了研究.对不同粒径的Fe3O4纳米颗粒按不同比例与PDMS混合形成的复合材料进行了测试.研究表明,与无磁场情况相比,在外磁场作用下,Fe3O4纳米颗粒/PDMS复合材料的电容值和介电损耗均发生了改变,产生了磁电容效应.由该复合材料磁电容效应所产生的电容变化量随着纳米颗粒混合浓度的增大而增大,并且当纳米颗粒粒径尺寸大于常温超顺磁临界尺寸时,材料的电容变化量随着颗粒尺寸的减小而增大. 相似文献
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Saurabh SahuRaj Kumar Dutta 《Journal of magnetism and magnetic materials》2011,323(7):980-987
A novel hybrid nanostructured material comprising superparamagnetic magnetite nanoparticles (MNPs) and pectin was synthesized by crosslinking with Ca2+ ions to form spherical calcium pectinate nanostructures, referred as MCPs, which were typically found to be 100-150 nm in size in dried condition, confirmed from transmission electron microscopy and scanning electron microscopy. The uniform size distribution was revealed from dynamic light scattering measurement. In aqueous medium the MCPs showed swelling behavior with an average size of 400 nm. A mechanism of formation of spherical MCPs is outlined constituting a MNP-pectin interface encapsulated by calcium pectinate at the periphery, by using an array of characterization techniques like zeta potential, thermogravimetry, Fourier transformed infrared and X-ray photoelectron spectroscopy. The MCPs were stable in simulated gastrointestinal fluid and ensured minimal loss of magnetic material. They exhibited superparamagnetic behavior, confirmed from zero field cooled and field cooled profiles and showed high saturation magnetization (Ms) of 46.21 emu/g at 2.5 T and 300 K. Ms decreased with increasing precursor pectin concentrations, attributed to quenching of magnetic moments by formation of a magnetic dead layer on the MNPs. 相似文献
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Microwave-assisted synthesis and magnetic property of magnetite and hematite nanoparticles 总被引:1,自引:0,他引:1
Nanoparticles of magnetite (Fe3O4) and hematite (α-Fe2O3) have been prepared by a simple microwave heating method using FeCl3, polyethylene glycol and N2H4·H2O. The amount of N2H4·H2O has an effect on the final phase of Fe3O4. The morphology of α-Fe2O3 was affected by the heating method. Crystalline α-Fe2O3 agglomerates were formed immediately at room temperature and most of these nanoparticles within agglomerates show the same
orientation along [110] direction. After microwave heating, ellipsoidal α-Fe2O3 nanoparticles were formed following an oriented attachment mechanism. Both Fe3O4 and α-Fe2O3 nanoparticles exhibit a small hysteresis loop at room temperature. 相似文献
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Magnetic iron oxide nanoparticles: Synthesis and surface coating techniques for biomedical applications 下载免费PDF全文
Iron oxide nanoparticles are the most popular magnetic nanoparticles used in biomedical applications due to their low cost, low toxicity, and unique magnetic property. Magnetic iron oxide nanoparticles, including magnetite (Fe304) and maghemite (γ-Fe203), usually exhibit a superparamagnetic property as their size goes smaller than 20 nm, which are often denoted as superparamagnetic iron oxide nanoparticles (SPIONs) and utilized for drug delivery, diagnosis, therapy, and etc. This review article gives a brief introduction on magnetic iron oxide nanoparticles in terms of their fundamentals of magnetism, magnetic resonance imaging (MRI), and drug delivery, as well as the synthesis approaches, surface coating, and application examples from recent key literatures. Because the quality and surface chemistry play important roles in biomedical applications, our review focuses on the synthesis approaches and surface modifications of iron oxide nanopar- ticles. We aim to provide a detailed introduction to readers who are new to this field, helping them to choose suitable synthesis methods and to optimize the surface chemistry of iron oxide nanoparticles for their interests. 相似文献
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《Current Applied Physics》2014,14(5):798-804
The article presents results of a study of TEMPO-labeled polymer coated superparamagnetic iron(II,III) oxide nanoparticles using both Electron Paramagnetic Resonance (EPR) spectroscopy and Electron Paramagnetic Resonance imaging technique (EPRI). The X-band (9.4 GHz) EPR spectroscopy was used to investigate the behavior of TEMPO-labeled polymer coated magnetite nanoparticles in different conditions (temperature and orientation in magnetic field). The broad line, which comes from the core of Fe3O4 nanoparticles, shows anisotropy. This signal broadens with decreasing temperature, its intensity increases with increasing temperature and the g factor decreases with increasing temperature. The shape of the signal from nitroxide radical strongly depends on temperature. When temperature is higher than 200 K, a narrow triplet appears, but when it is lower than 200 K the signal consists of broad asymmetric lines. Analysis of the signal allowed characterization of the motion of the spin label attached to nanoparticles. Values of anisotropy parameter ɛ and rotational correlation time τc were calculated for TEMPO in the fast rotation regime.The ability of TEMPO-labeled PEG coated magnetite nanoparticles to diffuse within the hydrogel medium was also investigated. The EPR imaging of nanoparticles diffusion in hydrogel was made at room temperature using an EPR L-band (1 GHz) spectrometer. EPRI has been proved effective for evaluation of changes in the spatial distribution of nanoparticles in the sample. 相似文献
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Fe3O4是一种重要的磁性材料.由于其独特的光、电、磁、热等性能而备受关注.在本文中,我们采用水热溶剂热法合成了Fe3O4磁性纳米粒子.利用X-射线衍射仪(XRD)、场发射扫描电子显微镜(FESEM)和振动样品磁强计(VSM)对产物的结构、形貌及磁性能进行了研究.结果表明,通过前驱物的适当选择,可以实现Fe3O4纳米粒... 相似文献
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Mehmet Gokhan Caglayan Hilal Torul Feyyaz Onur Ugur Tamer 《Journal of Raman spectroscopy : JRS》2015,46(9):802-806
In this paper, we proposed two sensitive surface‐enhanced Raman spectroscopy assays for the determination of modafinil in urine matrix. In the first assay, modafinil was extracted by solid phase extraction and determined after sandwiching with silver nanoparticles. In the second assay, modafinil was extracted by non‐specific interaction with magnetic gold nanoparticles and determined by sandwiching with magnetic gold and silver nanoparticles. The non‐specific magnetic extraction does not require any analyte specific agent like antibody, aptamer, or molecularly imprinted polymer, therefore, the cost and complexity of the assay is very low. Both assays are capable for application to urine samples with the detection limits under the minimum required performance limit of modafinil. The assays were validated in terms of accuracy, precision, detection limits, and ranges. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
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Marchegiani G Imperatori P Mari A Pilloni L Chiolerio A Allia P Tiberto P Suber L 《Ultrasonics sonochemistry》2012,19(4):877-882
Hydrophilic magnetite nanoparticles in the size range 30-10 nm are easily and rapidly prepared under ultrasonic irradiation of Fe(OH)2 in di- and tri-ethylene glycol/water solution with volume ratio varying between 7:3 and 3:7.Structural (XRD) and morphological (SEM) characterization reveal good crystalline and homogeneous particles whereas, when solvothermally prepared, the particles are inhomogeneous and aggregated. The sonochemically prepared particles are versatile, i.e. well suited to covalently bind molecules because of the free glycol hydroxylic groups on their surface or exchange the diethylene or triethylene glycol ligand. They can be easily transferred in hydrophobic solvents too.Room-temperature magnetic hysteresis properties measured by means of Vibrating Sample Magnetometer (VSM) display a nearly superparamagnetic character.The sonochemical preparation is easily scalable to meet industrial demand. 相似文献
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基于微磁学模拟方法研究末端形状对NiFe纳米薄膜的磁反转和自旋波本征动力学特性的调制及磁反转与自旋波模式软化间的内在联系.纳米薄膜微磁结构的相变总是伴随着某种自旋波模式的软化,软化自旋波模式空间分布预示微磁结构相变的路径.存在一临界裁剪度(h0).当裁剪度h<h0时,磁振荡局域于末端边缘的EM自旋波软化诱导磁反转从磁体末端边缘磁矩失稳开始,边缘失稳区域向中央扩展形成反转畴,最后反转畴逐渐移出膜面外而实现反转.当h≥h0时,形状各向异性导致边缘局域化模式自旋波被抑制,反转场附近一致模式自旋波的软化诱导磁体一致反转. 相似文献
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We simulated the asymmetrical growth of cube-shaped nanoparticles by applying the Monte Carlo method.The influence of the specific mechanisms on the crystal growth of nanoparticles has been phenomenologically described by efficient growth possibilities along different directions(or crystal faces).The roles of the thermodynamic and kinetic factors have been evaluated in three phenomenological models.The simulation results would benefit the understanding about the cause and manner of the asymmetrical growth of nanoparticles. 相似文献