La0.25Ca0.75MnO3的晶体结构研究

用X射线衍射仪测量了La0．25Ca0．75MnO3多晶粉末在300K和70K时的晶体结构衍射谱，并用Rietveld全谱拟合法对这些数据进行了拟合．结果表明，在室温时，La0．25Ca0．75MnO3由于MnO6八面体的Jahn-Teller晶格畸变，其晶体结构已发生了扭曲，晶格常数分别为a=0．53559nm，b=0．75537nm，c=0．53587nm．温度降至70K时，X射线衍射谱上出现了比室温更多的衍射峰，有些峰发生了“双峰”劈裂，但仍然具有与室温相同的晶体对称性(空间群为Prima)．70K时的晶格常数分别为a=0．53673nm，b=O．74785nm，c=O．53718nm，与300K时的晶格常数比较，a和c分别增大了O．21％和O．24％，而b减小了1．O％，这一晶体结构的巨大变化源于在电荷有序态下形成了静态的合作Jahn-Teller效应．     

Magnetic Properties and Magnetoresistance of HfFe6Ge6—Type Er1—xGdxMn6Ge6 and Ho1—xGdxMn6Ge6（0.2≤x≤0.9） Compounds

Magnetic properties and magnetoresistance effects of the Er1-xGdxMn6Ge6 and Ho1-xGdxMn6Ge6 (0.2≤x≤0.9) compounds have been studied by magnetic property and resistivity measurements in applied magnetic field up to 5T. For increasing Gd content, two series display a transition from the antiferromagnetic state to the ferrimagnetic state. The Er1-xGdxMn6Ge6 (x=0.2 and 0.5) and Ho1-xGdxMn6Ge6(x=0.2 and 0.4) compounds order antiferromagnetically at 430,432,423 and 425K, respectively. The Er1-xMn6Ge6 (x=0.8 and 0.9) and Ho1-xGdxMn6Ge6(x=0.7,0.8 and 0.9) compounds order ferrimagnetically at 462, 471, 450, 463 and 470K, respectively. The Er1-xGdxMn6Ge6 and Ho1-xGdxMn6Ge6 compounds undergo the second transitions below 71 and 82K, respectively. The magnetoresistance curves of the Er0.1Gd0.9Mn6Ge6 and Ho0.1Gd0.9Mn6Ge6 compounds in a field of 5T are presented and the magnetoresistance effects are related to the metamagnetic transistions.     

用Diamond TG/DTA热重/差热综合热分析仪在外加磁场下研究磁性材料相转变

介绍综合热分析仪Diamond TG/DTA在磁性材料研究中的应用.提出在外加磁场作用下,得到样品的热重曲线(TG),由TG曲线分析样品磁性相变及样品居里温度变化的原因,看到稀土铁基金属间化合物样品替代的Co元素的站位和元素之间相互作用对居里温度有很大影响.作为一种测量居里温度的方法,拓展Diamond TG/DTA热分析仪应用研究领域.     

Ferrimagnetic ceramic adsorbents for cleanup of H2S from exhaust gases

Adsorbents that exhibit magnetic properties in addition to other required process-relevant characteristics open up new perspectives for the dry reduction and/or elimination of HES and other sulfur compounds from exhaust gases. These adsorbents eliminate the sulfur compounds from exhaust gases by virtue of their coatings and their magnetic property which makes it possible the use of magnetically assisted and stabilized fluidization in an externally applied magnetic field. In the present paper, the feasibility of the sorptive function of porous ceramic ferrimagnetic beads is ensured by sol-gel coating of zinc oxide without the formation of Zn-Fe-oxides and without considerable decrease of available pore volume. The results of material characterization by SEM, Auger electron spectroscopy, X-ray and mercury-porosity measurements and the loading capacity of a HES/N2 model gas are presented and discussed. The resulting HES loading of the functionalized adsorbent beads is more than 10 times larger than that of the starting material. @ 2007 Chinese Society of Particuolo~v and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V.     

基于电阻型频率选择表面的宽带雷达超材料吸波体设计

将多边开缝式电阻型频率选择表面 (frequency selective surface, FSS)与传统的磁性吸波材料(radar absorption materials, RAM)复合, 提出了一种新型吸波体模型. 在分析该模型材料结构和拓扑结构的基础上, 得到等效电路模型; 基于传输线理论获得该模型的反射率及输入阻抗. 采用CST仿真软件对电阻型FSS与无电阻型FSS进行对比仿真, 通过分析吸波效率, 结果表明电阻型FSS在8.7 GHz附近具有更加优良的吸波性能, 实物测试结果与仿真结果一致. 同时FSS复合传统的磁性吸波材料RAM 产生了拓频效果, 在8–15 GHz范围内起到全频段吸收.     

热液法制备磁性纳米材料

磁性纳米材料作为新兴的无机功能材料,因其具有与常规材料不同的特殊性质,如高比表面积、强磁响应性、良好的化学稳定性和生物相容性等,被广泛应用在生物合成、生物分离、生物传感器、免疫测定、有机催化、药物传输、数据存储和环境治理等方面。目前合成磁性纳米材料的方法主要有化学共沉降法、高温热分解法、溶胶-凝胶法及热液法等。由于热液法具有条件简易、成本低廉、反应活性高、产率可观和绿色环保等优势,近年来受到了广泛的关注,并已应用在工业生产中。本文根据磁性材料组成与构成方式的不同,综述了热液法合成磁性纳米材料的研究进展。     

ICF用磁性玻璃靶丸悬浮磁场的确定及材料制备初步研究

 根据靶丸悬浮原理,推导出ICF用磁性靶丸在悬浮磁场中受力的函数关系式,从而得到了靶丸悬浮的理论模型。通过实验和理论相结合的方法,得出当靶丸中磁性材料掺入质量百分比由1%增加到6%时,靶丸的磁场强度由0.09 mT增加到0.44 mT,而对应的外界悬浮磁场由0.93 mT减小到0.23 mT。     

B2O3掺杂对纳米Mn-Zn铁氧体烧结性能的影响

针对目前的纳米材料掺杂不均,易导致烧结后材料性能差等问题.本文将掺杂物B2O3制成水溶液,然后再与Mn-Zn铁氧体纳米粉体进行混合,以提高B2O3分布的均匀度.研究结果表明:随着B2O3掺杂量的增加,烧结后材料的各项性能呈抛物线规律变化,并于B2O3掺杂量为0.15wt;时达到极值.与未掺杂的材料相比,虽然材料的饱和磁化强度、起始磁导率、居里点及截止频率有不同程度下降,但其功率损耗特性却显著改善.这应得益于B2O3的均匀掺杂使得烧结后材料的致密度提高(相对密度约为98;)以及微观组织的改善.     

单分子磁体及其磁学表征*

单分子磁体是介于分子基磁体和纳米磁性材料的学科交叉点.对其不同寻常磁特性的研究不仅有助于纳米磁性离子物理学和化学的发展,而且有望最终用于高密度信息储存设备.本文就单分子磁体的研究背景和意义、单分子磁体的种类、结构及磁学表征作一概述.     

Bulk—like contribution of tunnel magnetoresistance in magnetic tunnel junctions

We have demonstrated that the bulk-like contribution to tunnelling magnetoresistance (TMR) exists in the magnetic tunnel junctions, and is determined by the tunnelling characteristic length of the ferromagnetic electrodes. In the experiment, a wedge-shaped CoFe layer is inserted at the interface between the insulating barrier and the reference electrode. It is found that TMR ratio increases from 18% without CoFe layer to a saturation value of 26.5% when the CoFe thickness is about 2.3 nm. The tunnelling characteristic length, l_{tc}, can be obtained to be about 0.8 nm for CoFe materials.