包钴铁氧体型γ-Fe_2O_3磁粉穆斯堡尔效应的研究

包钴铁氧体型,γ-Fe_2O_3磁粉(简记为CoFe-γ-Fe_2O_3)是针状γ-Fe_2O_3磁粉与Co~( )和Fe~( )溶液起反应,在每个针状颗粒上包覆了一层钴铁氧体固溶体。经此种方法处理后的γ-Fe_2O_3磁粉的矫顽力及其它磁特性有较大的提高。如矫顽力由原来415Oe增加到715Oe;剩磁和矫顽力随时间及温度变化小等。我们利用穆斯堡尔效应并配合其它研究手段进行了研究,认为:CoFe-γ-Fe_2O_3磁粉矫顽力的提高,主要是由于γ-Fe_2O_3磁粉表面包覆了一层钴铁氧体固溶体,γ-Fe_2O_3与钴铁氧体固溶体之间发生磁耦合作用之故。     

包钴型γ-Fe_2O_3磁粉矫顽力的研究

包钴型γ-Fe_2O_3磁粉分为包钴γ-Fe_2O_3(简记为Co-γ-Fe_2O_3)和包钴包亚铁γ-Fe_2O_3(简记为 CoFe-γ-Fe_2O_3)两种,它们的矫顽力可比γ-Fe_2O_3磁粉的提高100至400Oe左右,本工作对这两种磁粉矫顽力增大的原因作了探讨,认为它们矫顽力增大的机制不同:CO-γ-Fe_2O_3矫顽力增大是由于表面包覆一层Co(OH)_2使表面各向异性增大,而CoFe-γ-Fe_2O_3则是由于表面包覆的是钴铁氧体,γ-Fe_2O_3与钴铁氧体之间发生耦合作用,使矫顽力增大。     

包钴型γ—Fe_2O_3磁粉矫顽力增大原因的探讨

针状γ-Fe_2O_3磁粉与Co~(++)和Fe~(++)溶液或Co(OH)_2起反应,在每颗颗粒上包上了一层Co铁氧体。经这样处理后的γ-Fe_2O_3磁粉的矫顽力可由原来的420Oe增大到770Oe左右。研究了这种磁粉的矫顽力H_c随磁粉密度以及温度的变化等,认为这种磁粉矫顽力增大的原因是由于增加了磁粉的表面各向异性所致     

包钴型r-Fe_2O_3磁粉各向异性研究

包钴型γ-Fe_2O_3磁粉的矫顽力可比原γ-Fe_2O_3磁粉提高8000—32000A/m。木文研究探讨了两种包钴型γ-Fe_2O_3磁粉(包钴γ-Fe_2O_3和包钴包亚铁γ-Fe_2O_3)的单轴各向异性的起源和矫顽力增大的机制。包钴γ-Fe_2O_3磁粉矫顽力增大是由于钴离子在γ-Fe_2O_3表面从尤取向产生表面单轴各向异性。包钴包亚铁γ-Fe_2O_3磁粉(Co~(2+)/γ-Fe_2O_3=2—16wt％)的矩形比S.R.为0.5左右,包钴包亚铁后增强的单轴各向异性和多轴磁晶各向异性使矫顽力增大。增强的单轴各向异性的起源:(1)钴离子在γ-Fe_2O_3表面从尤取向产生表面单轴各向异性;(2)表面层钴铁氧体微晶易磁化轴从尤排列显示单轴各向异性。     

金属离子掺杂对CuO基纳米复合材料的交换偏置调控

为了研究反铁磁基体中掺杂的金属离子对交换偏置效应的影响, 本文采用非均相沉淀法制备了纳米复合材料. X射线衍射图(XRD)和场发射扫描电子显微镜(SEM) 照片清晰表明CuO纳米复合样品具有统一的颗粒尺寸, 约为80 nm. 通过体系中掺杂磁性金属离子Ni和Fe, 实现了亚铁磁MFe₂O₄ (M=Cu, Ni)晶粒镶嵌在反铁磁(AFM) CuO 基体中. 在CuO基体中加入少量的Ni能改变两相交界面的磁无序从而生成类自旋玻璃相, 相应提高对铁磁相磁矩的钉扎作用. 同时, 场冷过程中反铁磁相内形成磁畴, 冻结在原始状态或磁场方向上, 畴壁也起到钉扎铁磁自旋的作用, 进而提高交换偏置效应. 随后加入的Ni 会生成各向异性能较大的NiO, 也能够提高交换偏置场. 在带场冷却下, 所有样品均发生垂直交换偏置, 也证明了样品在场冷过程中形成了自旋玻璃相, 正是由于亚铁磁与自旋玻璃相界面上的磁交换耦合, 才导致回线在整个测量范围内发生了向上偏移. 零场冷却和场冷却(ZFC/FC)情况下磁化强度与温度变化曲线(M-T)说明在这些复合材料中的交换偏置效应是由于存在亚铁磁颗粒和类自旋玻璃相界面处的交换耦合作用. 研究发现随着持续掺杂Ni离子, 交换偏置场先缓慢增加后又急剧增加, 生成各向异性能高的反铁磁相NiO 和反铁磁相内的畴态组织是这一结果的原因.     

Co处理的γ-Fe_2O_3薄膜的界面研究

本文中对CoO与Fe_2O_3的界面进行了研究,结果表明,简单的CoO-γ-Fe_2O_3界面对于磁性能基本无影响。分析表明,“复杂的扩散界面”不大可能象以往认为的那样是矫顽力增长的主要原因。矫顽力的增长可能是由掺Co造成的一种体效应而不是界面效应。     

Cr/Ru/PtCo/Ru/PtCo/Ru介质中底层Ru厚度对磁记录特性影响的研究

讨论了Cr/Ru（1）/PtCo（稳定层）/Ru（2）/PtCo（记录层）/Ru（3） 结构的矫顽力Hc_c与层间反铁磁耦合交换场Hex_ex随Ru（1）与Ru（2）厚度变 化的规律.研究发现 ，样品的矫顽力及交换场随Ru（1）厚度增加而增大， 这可能是由Ru（1）hcp结构引起的. 矫顽力及交换场在Ru（2）厚度为08nm处有峰值. 关键词： 磁记录 反铁磁耦合     

FeMn掺杂AlN薄膜的制备及其特性研究

采用直流磁控共溅射技术, 以Ar与N₂为源气体, 硅片为衬底成功地制备了Fe, Mn掺杂AlN薄膜. 利用X射线衍射和拉曼光谱研究了工作电流、靶基距离等工艺参数的改变对薄膜结构的影响. 利用扫描电子显微镜和能谱分析仪对薄膜的表面形貌和组成成分进行了分析. 利用振动样品磁强计在室温下对Fe, Mn掺杂AlN薄膜进行了磁性表征. Mn掺杂AlN薄膜表现出顺磁性的原因可能是由于Mn掺杂浓度较高, 在沉积过程部分Mn以团簇的形式存在, 反铁磁性的Mn团簇减弱了体系的铁磁交换作用. Fe掺杂AlN薄膜表现出室温铁磁性, 这可能是AlFeN三元化合物作用的结果. 随着Fe 掺杂AlN薄膜中Fe原子浓度从6.81%增加到16.17%, 其饱和磁化强度M_s由0.27 emu·cm^-3逐渐下降到0.20 emu·cm^-3, 而矫顽力H_c则由57 Oe增大到115 Oe (1 Oe=79.5775 A/m), 这一现象与Fe离子间距离的缩短及反铁磁耦合作用增强有关. 关键词： 直流磁控共溅射 氮化铝薄膜 结构 磁性     

γ-Fe_2O_3中的氢含量

利用热中子透射法测定γ-Fe_2O_3的氢含量。利用差热分析、磁分析以及穆斯堡尔效应研究γ-Fe_2O_3的相变,实验结果表明在γ-Fe_2O_3结构中确实含有一定量的氢,当γ-Fe_2O_3结构中的阳离子空位被H~(1 ),Co~(2 ),Si~(4 ),P~(5 )等离子占据时,将有利于γ-Fe_2O_3晶体结构的稳定,从而使γ-Fe_2O_3转变为α-Fe_2O_3的相变温度有所提高。     

Ni81Fe19/Cr82Al18双层膜中的交换偏置

研究了直流磁控溅射法制备的Ni₈₁Fe₁₉/Cr₈₂Al₁₈双层膜中的交换耦合.样品的室温矫顽力与1/t^{3/2_FM(t_FM为铁磁层厚度）近似成正比例关系,从而表明在Ni₈₁Fe₁₉/Cr₈₂Al₁₈中交换耦合为铁磁/反铁磁界面的随机相互作用.另外还讨论了反铁磁层厚度对交换偏置的影响. 关键词：}     

高温高压方法合成碳包覆γ-Fe_2O_3纳米棒及其磁学性能

采用高温高压(HPHT)方法,以水热法制备的聚乙烯醇包覆FeOOH纳米棒为前驱体,合成了碳包覆γ-Fe2O3纳米棒.通过使用多种表征方法,研究了HPHT过程中合成温度对样品结构和形貌的影响,并对样品的生长机理进行了探讨.利用振动样品磁强计测量了样品的室温磁学性质.实验结果表明,反应温度为400?C,压强为1 GPa条件下制备的碳包覆γ-Fe2O3纳米棒具有较高的长径比(直径约为20 nm,长度约为150 nm),矫顽力可达到330 Oe(1 Oe=79.5775 A/m).该方法为制备具有核壳结构的一维纳米材料提供了新思路.     

First-principles Study on the Magnetic,Half-metal and Thermoelectric Transport Properties of Inorganic-Organic Hybrid Compounds [C4N2H12][Fe4Ⅲ(HPO3)2(C2O4)3]

The electronic structure, magnetic and half-metal properties of inorganic-organic hybrid compound [C₄N₂H₁₂][Fe₄^Ⅲ(HPO₃)₂(C₂O₄)₃] are investigated by using the full-potential linearized augmented plane wave (FPLAPW) method within density-functional theory (DFT) calculations. The density of states (DOS), the total energy of the cell and the spontaneous magnetic moment of [C₄N₂H₁₂][Fe₄^Ⅱ(HPO₃)₂(C₂O₄)₃] are calculated. The calculation results reveal that the low-temperature phase of [C₄N₂H₁₂][Fe₄^Ⅲ(HPO₃)₂(C₂O₄)₃] exhibits a stable ferromagnetic (FM) ground state, and we find that this organic compound is a half-metal in FM state. In addition, we have calculated antiferromagnetically coupled interactions, revealing the existence of antiferromagnetic (AFM), which is in agreement with the experiment. We have also found that [C₄N₂H₁₂][Fe₄^Ⅲ(HPO₃)₂(C₂O₄)₃] is a semiconductor in the AFM state with a band gap of about 0.40 eV. Subsequently, the transport properties for potential thermoelectric applications have been studied in detail based on the Boltzmann transport theory.     

包钴铁氧体型γ-Fe2O3磁粉穆斯堡尔效应的研究

包钴铁氧体型,γ-Fe₂O₃磁粉(简记为CoFe-γ-Fe₂O₃)是针状γ-Fe₂O₃磁粉与Co⁺⁺和Fe⁺⁺溶液起反应,在每个针状颗粒上包覆了一层钴铁氧体固溶体。经此种方法处理后的γ-Fe₂O₃磁粉的矫顽力及其它磁特性有较大的提高。如矫顽力由原来415Oe增加到715Oe;剩磁和矫顽力随时间及温度变化小等。我们利用穆斯堡尔效应并配合其它研究手段进行了研究,认为:CoFe-γ-Fe₂O₃磁粉矫顽力的提高,主要是由于γ-Fe₂O₃磁粉表面包覆了一层钴铁氧体固溶体,γ-Fe₂O₃与钴铁氧体固溶体之间发生磁耦合作用之故。 关键词：     

Surface termination, composition and reconstruction of Fe3O4(001) and γ-Fe2O3(001)

We address a current controversy concerning the nature of the surfaces of Fe₃O₄(001) and γ-Fe₂O₃(001) grown on MgO(001) by molecular beam epitaxy. Despite recent claims to the contrary, we show that γ-Fe₂O₃(001) unambiguously exhibits a (1×1) surface net, in contrast to Fe₃O₄(001), which assumes a R45 reconstruction. In addition, we present high-energy-resolution Fe 2p and O 1s core-level photoelectron spectra obtained at both normal and grazing emission for γ-Fe₂O₃(001) and Fe₃O₄(001). These spectra show that the Fe₃O₄(001) surface has a higher Fe(III)/Fe(II) ratio than the bulk, and that the asymmetry in the O 1s line shape for Fe₃O₄(001) is due to final state effects rather than the presence of a surface oxygen or hydroxyl species.     

超细颗粒γ-Fe2O3微粉包钴前后的各向异性

本工作利用穆斯堡尔谱并配合其它研究手段,测量了超细γ-Fe₂O₃微粉在包钴和不包钴两种情况下的各向异性常数K;观察到前者比后者的各向异性常数K增加30％左右。对普通针状包钴型γ-Fe₂O₃磁粉矫顽力增大的原因提供了进一步的说明。 关键词：     

Fe3O4纳米粒子对P3HT:PCBM电池的影响

为了提高太阳能电池的性能,研究磁性纳米粒子在外加磁场的作用下对聚合物太阳能电池有源层P3HT:PCBM成膜及太阳能电池性能的影响。本文采用热分解法制备了磁性Fe₃O₄纳米粒子,将不同质量分数的Fe₃O₄纳米粒子掺入到P3HT:PCBM溶液中,旋涂后在外加磁场的作用下自组成膜。通过TEM、XRD对制备的Fe₃O₄纳米粒子进行表征,并利用偏光显微镜、原子力显微镜对成膜质量进行探究。结果表明,采用热分解法制备的Fe₃O₄纳米粒子直径在10 nm左右,在外加磁场作用下,Fe₃O₄纳米粒子对成膜有一定的调控作用。当Fe₃O₄纳米粒子掺杂质量分数为1%时,太阳能电池器件的开路电压增加3.77%,短路电流增加24.93%,光电转换效率提高7.82%。     

Magnetic properties of aerosol synthesized iron oxide particles

Fine iron oxide particles have been prepared by an aerosol technique. The particles are spherical with a mean size of 0.1 μm. Heat treatment in air or nitrogen at various temperatures for various times leads to a variety of phase mixtures of -Fe₂O₃, γ-Fe₂O₃ and Fe₃O₄. The magnetic properties of these various samples are presented.     

The thermal spreading of antimony oxides onto Fe2O3

The uniform antimony-rich surface layer on Fe₂O₃ was carried out via thermal spreading of Sb₂O₃ and Sb₂O₄. TG–DTA results indicate that the oxidation temperature of Sb₂O₃ was decreased ca. 100 K due to thermal spreading effect. Although Sb₂O₄ is almost catalytically inert for oxidation of isobutane and Fe₂O₃ is a typical non-selective catalyst for this reaction, the formation of antimony-rich layer suppresses the combustion reactions and favors the partial oxidation reactions. When Sb₂O₄ instead of Sb₂O₃ was used as antimony resource, the enrichment of antimony on Fe₂O₃ surface was much lower. However, the reaction atmosphere of isobutane oxidation enhances antimony spreading over Fe₂O₃ surface. According to Mars–Van Krevelen mechanism, some Sb₂O₄ in catalysts could be intermediately reduced into Sb₂O₃ during reaction of isobutene oxidation, which thermal spreading is much easier. As shown by Raman results, the Sb₂O₄ that has been spread on Fe₂O₃ surface is probably amorphous.     

Magnetoresistance of Fe3O4/Au/Fe3O4 and Fe3O4/Au/Fe spin-valve structures

A detailed study of the in-plane magnetotransport properties of spin valves with one and two Fe₃O₄ electrodes is presented. Fe₃O₄/Au/Fe₃O₄ spin valves exhibit a clear anisotropic magnetoresistance in small magnetic fields but no giant magnetoresistance (GMR). The absence of GMR in these structures is due to simultaneous magnetization reversal in the two Fe₃O₄ layers. By contrast, a negative GMR effect is measured on Fe₃O₄/Au/Fe spin valves. The negative GMR is attributed to an electron spin scattering asymmetry at the Fe₃O₄/Au interface or an induced spin scattering asymmetry in the Au interfacial layers.     

Correlation of the activation volume with the crystallite size in λ-Fe2O3 and Co-modified λ-Fe2O3 fine particles

The activation volume and the crystallite size λ-Fe₂O₃ and Co-modified λ-Fe₂O₃ particles have been determined. For fixed particle volume the variation tendencies of the activation volume and crystallite size are the same. It seems to be that the crystallite size influences the activation volume in these materials.