外磁场对La-Co纳米管和纳米线磁性能的影响
发布时间：2018-12-16 19:31
【摘要】：通过稳恒电压沉积法,在孔径大小均匀、排列规整的氧化铝模版(AAO)中制备出了La-Co合金纳米管、纳米线阵列。模版法制备纳米材料具有易于控制其的长度、直径、壁厚且成本低等优点而被广泛应用。利用X射线衍射仪(XRD)对制备好的样品进行扫描检测,从获得的衍射图谱中判定其晶体结构类型；扫描电子显微镜(SEM)、透射电子显微镜(TEM)是观测样品形貌特征、研究样品几何尺寸的主要手段,并且使用SEM自带的能量弥散X射线谱仪(EDS)对纳米管、纳米线中化学元素及其含量进行定性、定量分析,而透射电镜的选区电子衍射图也将是分析样品晶体结构的有效途经,最后利用振动样品磁强计(VSM)对不同沉积条件下样品磁性能的变化做了详细的分析。结果显示,由于纳米管、纳米线的晶粒随机生长、无最优取向而导致其显示为非晶体结构。随着沉积电压绝对值的增大,其所含的Co元素都越来越少,对应的La含量比例则在升高,磁性能也越来越弱,磁各向异性也变得不再显著,饱和磁场则是逐渐增大。对其磁性能进行研究,结果显示易磁化轴方向垂直于纳米管轴,而纳米线其易磁化轴则是顺着纳米线轴。这是由于纳米管、纳米线具有不同的几何结构致使决定易磁化轴方向的有效各向异性场不同而导致的,纳米管中静磁相互作用占据了主导地位,而纳米线形状各向异性与磁晶各向异性共同叠加占据了优势地位。在决定矫顽力大小的磁反转模式中,纳米管由平行轴线方向的卷曲反转模式转变为垂直轴线方向的横向磁畴壁位移模式,而纳米线的磁反转模式则是单一的一致转动。电沉积时外加方向垂直、平行于纳米管轴、纳米线轴的大小为1.5 T的外磁场。结果显示外磁场对纳米管的磁性能影响较为有限,这是由于非晶结构的纳米管没有很强的磁晶各向异性能而导致的。与纳米管不同的是,纳米线中有较多的、随机排列的晶粒,在外磁场He的作用下晶粒的磁矩趋向于磁场方向,故而使得感应磁各向异性在平行于纳米线轴方向有较大幅度的增加,平行方向的矫顽力也随之大幅增加,有效各向异性变的更为明显。垂直方向受限于有限的几何直径其感应磁各向异性能比较小,且方向垂直于纳米线轴,它与静磁相互作用相互叠加共同与形状各向异性场竞争,进一步削弱了形状各向异性场的优势,使得有效各向异性场进一步减小,矫顽力也相应变小。
[Abstract]:La-Co alloy nanotubes and nanowire arrays were prepared by steady voltage deposition method in (AAO) with uniform pore size and regular arrangement. The preparation of nanomaterials by template method has been widely used because of its advantages such as easy to control its length, diameter, wall thickness and low cost. X-ray diffractometer (XRD) was used to scan and detect the prepared samples, and the crystal structure types were determined from the obtained diffraction patterns. Scanning Electron microscope (SEM) (SEM), transmission electron microscope (TEM) is the main method to study the geometric size of the sample by observing the morphology of the sample, and using SEM's own energy dispersive X-ray spectrometer (EDS) to pair the nanotubes. The chemical elements and their contents in nanowires are qualitatively and quantitatively analyzed, and the selected electron diffraction patterns of transmission electron microscopy will also be an effective way to analyze the crystal structure of the samples. Finally, the variation of magnetic properties of samples under different deposition conditions is analyzed in detail by vibrating sample magnetometer (VSM). The results show that the nanowires exhibit amorphous structure due to their random growth and no optimal orientation. With the increase of the absolute value of deposition voltage, the content of Co elements decreases, the proportion of La content increases, the magnetic properties become weaker and weaker, the magnetic anisotropy becomes less significant, and the saturation magnetic field increases gradually. The results show that the magnetization axis is perpendicular to the nanotube axis, while the magnetization axis of the nanowires is along the nanowire axis. This is due to the difference in the effective anisotropy field which determines the direction of the magnetization axis due to the different geometric structure of nanotubes, in which the magnetostatic interaction dominates. The superposition of nanowire shape anisotropy and magnetocrystalline anisotropy is dominant. In the magnetic inversion mode, which determines the coercivity, the coiling inversion mode in parallel axis direction is changed into the transverse domain wall displacement mode in the vertical axis direction, while the magnetic inversion mode of the nanowire is a single uniform rotation mode. The external magnetic field of the nanowire is 1.5 T, parallel to the nanotube axis and perpendicular to the external direction during electrodeposition. The results show that the effect of external magnetic field on the magnetic properties of nanotubes is limited, which is due to the absence of strong magnetocrystalline anisotropy energy of amorphous nanotubes. Different from nanotubes, there are many randomly arranged grains in nanowires, and the magnetic moment of grain tends to the direction of magnetic field under the action of external magnetic field He. As a result, the induced magnetic anisotropy increases greatly in the direction parallel to the nanowires, and the coercivity in the parallel direction increases greatly, and the effective anisotropy becomes more obvious. The vertical direction is limited by the finite geometric diameter, and the inductive magnetic anisotropy energy is relatively small, and the direction is perpendicular to the nanowire, which superposes with the magnetostatic interaction and competes with the shape anisotropic field. The advantage of the shape anisotropic field is further weakened and the effective anisotropy field is further reduced and the coercivity is reduced accordingly.
【学位授予单位】：内蒙古大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB383.1
本文编号：2382928
[Abstract]:La-Co alloy nanotubes and nanowire arrays were prepared by steady voltage deposition method in (AAO) with uniform pore size and regular arrangement. The preparation of nanomaterials by template method has been widely used because of its advantages such as easy to control its length, diameter, wall thickness and low cost. X-ray diffractometer (XRD) was used to scan and detect the prepared samples, and the crystal structure types were determined from the obtained diffraction patterns. Scanning Electron microscope (SEM) (SEM), transmission electron microscope (TEM) is the main method to study the geometric size of the sample by observing the morphology of the sample, and using SEM's own energy dispersive X-ray spectrometer (EDS) to pair the nanotubes. The chemical elements and their contents in nanowires are qualitatively and quantitatively analyzed, and the selected electron diffraction patterns of transmission electron microscopy will also be an effective way to analyze the crystal structure of the samples. Finally, the variation of magnetic properties of samples under different deposition conditions is analyzed in detail by vibrating sample magnetometer (VSM). The results show that the nanowires exhibit amorphous structure due to their random growth and no optimal orientation. With the increase of the absolute value of deposition voltage, the content of Co elements decreases, the proportion of La content increases, the magnetic properties become weaker and weaker, the magnetic anisotropy becomes less significant, and the saturation magnetic field increases gradually. The results show that the magnetization axis is perpendicular to the nanotube axis, while the magnetization axis of the nanowires is along the nanowire axis. This is due to the difference in the effective anisotropy field which determines the direction of the magnetization axis due to the different geometric structure of nanotubes, in which the magnetostatic interaction dominates. The superposition of nanowire shape anisotropy and magnetocrystalline anisotropy is dominant. In the magnetic inversion mode, which determines the coercivity, the coiling inversion mode in parallel axis direction is changed into the transverse domain wall displacement mode in the vertical axis direction, while the magnetic inversion mode of the nanowire is a single uniform rotation mode. The external magnetic field of the nanowire is 1.5 T, parallel to the nanotube axis and perpendicular to the external direction during electrodeposition. The results show that the effect of external magnetic field on the magnetic properties of nanotubes is limited, which is due to the absence of strong magnetocrystalline anisotropy energy of amorphous nanotubes. Different from nanotubes, there are many randomly arranged grains in nanowires, and the magnetic moment of grain tends to the direction of magnetic field under the action of external magnetic field He. As a result, the induced magnetic anisotropy increases greatly in the direction parallel to the nanowires, and the coercivity in the parallel direction increases greatly, and the effective anisotropy becomes more obvious. The vertical direction is limited by the finite geometric diameter, and the inductive magnetic anisotropy energy is relatively small, and the direction is perpendicular to the nanowire, which superposes with the magnetostatic interaction and competes with the shape anisotropic field. The advantage of the shape anisotropic field is further weakened and the effective anisotropy field is further reduced and the coercivity is reduced accordingly.
【学位授予单位】：内蒙古大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB383.1
【参考文献】
相关期刊论文 前1条
1 高鹏;杨中东;薛向欣;樊占国;;磁场影响下的电沉积[J];材料保护;2006年08期
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