巨磁热效应与磁冰箱

 今天,电冰箱即使在我们这样发展中国家的城市中,也已经是很普通的家电,日常生活中缺之不得。无疑,电冰箱给人们带来了很多的便利。但是,电冰箱存在着两大缺点,一是使用压缩机,需要消耗不少的能量;二是其普遍使用氟立昂作为致冷剂,氟立昂(R12)的化学分子式是CCl2F,它是通常称之为氟氯烃(CFCs)的含氯源气体的一种,是破坏大气臭氧层的元凶之一。这也表明,科学技术是一把双刃剑。那么,能不能除去电冰箱这两大缺陷呢?科学技术的发展肯定地回答了这个问题,这就是5年前发现的巨磁热效应以及近一二年发明的室温磁冰箱。     

电介质的极化能与弱磁质的磁化能

本文从微观的角度用做功的方法计算了电介质的极化能量密度与弱磁质质的磁化能量密度。     

磁光Kerr效应的温度特性研究

从磁光Kerr效应的微观量子表述出发，分别研究了铁磁材料和亚铁磁材料的磁光Kerr效应的温度特性。结果表明，磁光Kerr转角θK与材料磁化强度随温度变化关系不同。铁磁材料θK对磁化强度M的级数展开式中仅含M奇次项。亚铁磁材料可以出现磁化强度M≠0而磁光Kerr转角θK=0情况。     

相分离Nd0.5Ca0.5MnO3体系的再入型自旋玻璃行为和电荷有序

K左右出现典型再入型自旋玻璃行为,同时观察到了负的磁化率异常. 结果表明,Nd0.5Ca0.5MnO3体系在低温下存在着典型的相分离和多种复杂的磁相互作用竞争机制,这为强关联锰氧化物体系物理机制的理解提供了重要的实验资料.     

甚高频用超低饱和磁化强度In∶BiCaVIG晶体生长及磁特性研究

利用加速坩埚转动技术制备了超低饱和磁化强度(M_s)石榴石型In∶BiCaVIG单晶铁氧体材料,系统研究了单晶样品的晶体结构、微观形貌及磁学性能。结果表明:In∶BiCaVIG单晶样品结晶良好,具有体心立方结构;样品的居里温度为104 ℃,饱和磁化强度为60 G,饱和磁化强度偏差达到±20 G, 略优于美国Microphere公司同类型材料产品。经过抛光处理后的球形样品线宽明显减小,最小线宽为5.8 Oe,这是因为化学抛光处理可以均匀腐蚀加工应力层,导致线宽减小。另外,与未掺杂BiCaVIG单晶相比,超低饱和磁化强度样品的线宽明显要大,这主要跟样品的饱和磁化强度大小有关。     

基于伊辛模型的Fe_(0.5)Mn_(0.1)Al_(0.4)合金磁化强度和磁熵变蒙特卡洛模拟

基于伊辛模型的单自旋反转蒙特卡洛算法,考虑了粒子间的最近邻以及次近邻相互作用,研究了无序Fe0.5Mn0.1Al0.4合金的磁化强度和磁熵变.首先,强调了粒子间的次近邻相关作用对体系的磁性和热力学性质的影响,明确了次近邻相互作用系数,证实了低温合金阻挫的存在;其次,研究了在相变温度处(不同磁场下)磁化强度随外加磁场(温度)的变化情况以及磁性粒子对磁化强度的贡献,发现反铁磁性粒子Mn在低温区对Fe0.5Mn0.1Al0.4合金的相变起了主要作用,而高温区体系的相变是由铁磁性粒子Fe贡献的;最后,分析了体系在相变温度处磁熵变数值随外加磁场的变化情况以及磁熵变在不同的外磁场下随温度的变化情况,当外加磁场H=0.14(a.u.)时,Mn粒子在冻结温度处的平均磁化强度为零,体系处于最无序的状态,对应的磁熵变ΔS(0.1,0.14)达到了正向最大值,极值的位置对应于体系的相变温度.     

Fabrication and Characterization of Mn0.5Zn0.5Fe2O4 Magnetic Nanofibers

Mn0.5Zn0.5Fe2O4 Magnetic nanofibers were fabricated by calcining electrospun polymer/inorganic composite nanofibers and characterized by thermogravimetric and differential thermal analysis, x-ray diffraction, field emission scanning electron microscopy, high resolution transmission electron microscopy and a vibrating sample magnetometer. The experimental results show that the pure spinel structure is basically formed when the composite nanofibers are calcined at 450°C for 2h. With the increasing calcination temperature, both the saturation magnetization and coercivity of nanofiber samples increase initially along with the growth of Mn0.5Zn0.5Fe2O4 nanocrystals contained in the nanofibers. However, when the calcination temperature reaches 550°C, the saturation magnetization of nanofibers starts to dramatically decrease owing to the formation of the α-Fe2O3 phase at this temperature. The prepared Mn0.5Zn0.5Fe2O4 nanofibers calcined at 500°C for 2h have diameters ranging from 100 to 200nm. Their saturation magnetization and coercivity are 12.37emu/g and 4.81kA/m at room temperature, respectively.     

Magnetic Properties of Ni-Zn Ferrite Prepared with the Layered Precursor Method

We prepare NiZnFe2O4 soft magnetic ferrites with different molar ratios with the layered precursor method and investigate their magnetic properties. In the layered precursor, metal ions are scattered on the layer plate in a certain way on account of the effect of lowest lattice energy and lattice orientation. After high temperature calcinations, spinel ferrites with uniform structural component and single magnetic domain can be obtained, and the magnetic property is improved greatly. NiZnFe2O4 ferrites prepared have the best specific saturation magnetization of 79.15 emu·g^-1, higher than that of 68 emu·g^-1 prepared by the chemical co-precipitation method and that of 59 emu·g^-1prepared by the emulsion-gel method. Meanwhile the coercivity of NiZnFe2O4 ferrites prepared by layered precursor method is 14 kA·m^-1, lower than that of 50 emu·g^-1 prepared by the co-precipitation method and that of 59 emu·g^-1 prepared by the emulsion-gel method.     

Fe/SBA-3介孔组装体系及其磁特性

用不同的实验工艺制备了一组Fe/SAB-3 介孔复合体系.X射线衍射表明,Fe/SAB-3具有六方排列的孔道结构.通过N2吸附实验可知,这种材料具有极高的比表面积.从傅立叶红外光谱可证实,Fe3＋进入了SAB-3的骨架.样品磁测量结果表明,与通常的α-Fe2O3纳米颗粒相比,纳米Fe/SAB-3介孔复合体系中的纳米α-Fe2O3 粒子的矫顽力（Hc）从1765 Oe下降到87 Oe,比饱和磁化强度（Ms）增加了75.4％.     

金刚石/Fe3O4磁性聚集磨料的制备与表征

以表面缺陷较多的金刚石微粉为实验原料,用混合强酸对其表面进行处理使其羟基和羧基化.然后采用化学沉淀法制备出金刚石/Fe3 O4磁性聚集磨料.用XRD、SEM、EDS、IR、Raman、VSM等检测方法对样品的结构、形貌、元素组成和磁性能进行了表征.结果表明,Fe3+与金刚石表面的含氧基团的络合作用,使金刚石微粉表面被Fe3 O4颗粒包裹,形成不规则类球形金刚石/Fe3 O4磁性聚集体.当金刚石加入量占理论生成总固体量的9.4wt;时,磁性聚集磨料展现较高的磁性能.其饱和磁化强度(Ms=60.8 emu/g)与同等工艺制备的纯Fe3O4样品(Ms=66.3 emu/g)接近.