材料结构对磁性的影响

发布时间：2018-10-17 17:34

【摘要】：近年来,随着纳米材料的开发和利用,材料结构和物性之间的关系越来越受到人们的关注。如人们为了提高多铁材料的磁电耦合,进行了大量的结构整合,尤其是多相复合多铁材料的研究已经成为该领域的研究热点。研究发现多相复合多铁材料的磁电耦合明显增强,但是其中的物理机制并不明了;另外,为了探明非磁性金属氧化物中室温铁磁性出现的物理机制,人们进行了各种尝试,发现其结构对于这类材料的铁磁性具有重要影响,但是其中的物理机制仍然众说纷纭,没有一个统一的结论。针对上述问题,本文制备了多相复合多铁材料和有序多孔ZrO_2薄膜,并对其结构和磁性之间的关系进了深入研究。具体结果如下:通过改变具有尖晶石结构的亚铁磁相CoFe_2O_4(CFO)的含量,采用固相反应法制备了一系列多铁材料Bi_(0.85)La_(0.15)FeO_3(BLFO)和CFO的两相复合材料;利用冷场发射扫描电子显微镜(FE-SEM)、X射线衍射仪(XRD)和X射线能量散射谱(EDS)对材料的结构和成分进行了表征,发现BLFO和CFO在制备过程中并没有发生化学反应,且BLFO的晶粒尺寸几乎不随着铁磁相的掺杂而变化;利用物理性能测试仪(PPMS)和铁电分析仪对BLFO-CFO两相复合材料的物性性能进行了测试,结果表明,随着铁磁相CFO掺杂含量的增加样品的饱和磁化强度和剩余极化强度都是增加的;我们在假定磁性完全来自于铁磁相CFO的基础上,对材料的磁化强度进行了理论计算,通过和实验测试得到的磁化强度的比较,发现理论值远小于实验值,由此证明了BLFO-CFO两相复合材料中存在较强的磁电耦合效应;由于该类复合材料的漏电流较大,因而实验上无法测得磁电耦合系数,因而上述结果也为该类复合样品中是否存在磁电耦合效应提供了一种新的证明方法。以有序多孔阳极氧化铝模板(PAA)为基底,采用反应直流磁控溅射的方法制备了有序多孔ZrO_2薄膜。通过XRD、FE-SEM和EDS等设备对材料的结构和成分进行了表征,发现随着溅射时间的增长,ZrO_2薄膜的孔径越来越小,厚度越来越大;通过PPMS和紫外可见分光光度计(UV-Vis)等手段对Zr O2薄膜的物性进行了测试。发现在室温下ZrO_2薄膜呈现出明显的铁磁性,而且当外加磁场垂直于薄膜表面时的磁性要大于平行于薄膜表面时的磁性,这说明ZrO_2薄膜具有磁各向异性,并且沿着孔的方向为易磁化方向,而且在孔径最大的薄膜上测试得到了约为119emu/cm3的最大的饱和磁化强度;对样品的退火处理以及PL测试结果表明,ZrO_2薄膜的磁性主要是依赖于薄膜中存在的单电子氧空位,并且可通过控制氧空位的多少来实现磁性的变化,这也表明ZrO_2薄膜有望应用到自旋电子器件上。
[Abstract]:In recent years, with the development and utilization of nanomaterials, more and more attention has been paid to the relationship between material structure and physical properties. For example, in order to improve the magnetoelectric coupling of ferromagnetic materials, a large number of structural integration has been carried out, especially the study of multiphase composite multi-iron materials has become a research hotspot in this field. It is found that the magnetoelectric coupling of multiphase composite polyferric materials is obviously enhanced, but the physical mechanism is not clear. In addition, in order to find out the physical mechanism of ferromagnetism in non-magnetic metal oxides at room temperature, various attempts have been made. It is found that its structure has an important influence on the ferromagnetism of this kind of materials, but the physical mechanism is still controversial, and there is no uniform conclusion. In order to solve the above problems, the multiphase composite multiferric materials and ordered porous ZrO_2 thin films have been prepared, and the relationship between the structure and magnetic properties has been studied in detail. The results are as follows: by changing the content of ferromagnetic phase CoFe_2O_4 (CFO) with spinel structure, a series of multiphase composite materials Bi_ _ (0.85) La_ _ (0.15) FeO_3 (BLFO) and CFO were prepared by solid state reaction. The structure and composition of the materials were characterized by cold field emission scanning electron microscopy (FE-SEM), X ray diffractometer (XRD) and X-ray energy scattering (EDS). It was found that there was no chemical reaction between BLFO and CFO during the preparation process. The grain size of BLFO hardly changes with the doping of ferromagnetic phase, and the physical properties of BLFO-CFO two-phase composites are tested by physical property tester (PPMS) and ferroelectric analyzer. The saturation magnetization and the remanent polarization strength of the samples are increased with the increase of the CFO doping content of the ferromagnetic phase, and the magnetization of the materials is calculated theoretically on the basis of the assumption that the magnetization comes entirely from the ferromagnetic phase CFO. Compared with the experimental results, it is found that the theoretical value is much smaller than the experimental value, which proves that there is a strong magnetoelectric coupling effect in the BLFO-CFO two-phase composite, because the leakage current of the composite is large, Therefore, the magnetoelectric coupling coefficient can not be measured experimentally, so the above results also provide a new proof method for the existence of magnetoelectric coupling effect in this kind of composite sample. The ordered porous ZrO_2 films were prepared by reactive DC magnetron sputtering on the substrate of ordered porous anodic alumina template (PAA). The structure and composition of the films were characterized by XRD,FE-SEM and EDS. It was found that with the increase of sputtering time, the pore size and thickness of ZrO_2 thin films became smaller and larger. The physical properties of Zr O 2 thin films were measured by means of PPMS and UV-Vis spectrophotometer (UV-Vis). It is found that ZrO_2 thin films exhibit obvious ferromagnetism at room temperature, and the magnetic properties of ZrO_2 thin films are larger when the applied magnetic field is perpendicular to the surface of the films than that of the films parallel to the surface of the films, which indicates that the ZrO_2 thin films have magnetic anisotropy. The maximum saturation magnetization of 119emu/cm3 is obtained on the thin films with the largest pore size, and the orientation of the pore is easy to be magnetized, and the maximum saturation magnetization is obtained on the thin films with the largest pore size. The annealing treatment and PL measurements show that the magnetic properties of ZrO_2 films are mainly dependent on the single electron oxygen vacancies in the films, and the magnetic changes can be realized by controlling the oxygen vacancies. This also indicates that ZrO_2 thin films are expected to be applied to spin electronic devices.
【学位授予单位】：河北师范大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB303

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