磁性纳米岛的物性研究

发布时间：2019-03-20 12:45

【摘要】：低维纳米材料是当前科学研究的热点之一,低维纳米材料包括二维、一维和零维纳米材料。其中零维纳米材料在材料结构上可以表现为量子点、纳米岛等。纳米岛是由有限数目的原子构成,在x-y平面及z方向上的尺寸均在纳米量级,被誉为是“人造原子”。纳米岛与其它磁性材料相比可以显著地提高比表面积,主要在磁储备装置、小结构高覆盖率太阳能电池、锂离子电池和光电探测器等有潜在的应用前景。因此,磁性纳米岛的理论研究对其应用有重要的指导意义。本文基于相关有效场理论研究了六角磁性纳米岛的物理特性。论文中,主要研究了各物理参数对磁性纳米岛的磁矩、磁化率、相变温度、磁滞回线、阶梯效应、内能、比热的影响。结果显示,改变交换耦合作用、磁晶各向异性和横场时,系统会出现重入现象,并且在一定参数范围内,系统会同时出现两个相变点和一个补偿点;随着各参数的变化,系统内能曲线会在不同的位置出现拐点,即相变温度不同;比热曲线在相变温度处会出现奇异现象,这是典型的二级相变特点;当系统处于低温时,在外场的作用下,磁矩表现出明显的阶梯效应,表面交换作用和磁晶各向异性对阶梯效应有重要影响;交换耦合作用、磁晶各向异性、横场及温度都会影响系统磁滞回线的环数及形状。基于相关有效场理论还研究了立方结构磁性纳米岛的物理特性。立方结构纳米岛的磁矩、相变温度及阶梯效应受核的磁晶各向异性影响较大。与六角结构纳米岛的变化规律类似,在一定的参数范围内,系统也出现了多个相变点。内能、比热曲线的变化趋势与六角结构纳米岛相似。在低温时,系统出现了磁矩阶梯和多环的磁滞回线。
[Abstract]:Low-dimensional nanomaterials, including two-dimensional, one-dimensional and zero-dimensional nanomaterials, are one of the hot spots in scientific research. The structure of zero-dimensional nano-materials can be represented as quantum dots, nano-islands and so on. The nano-island is composed of finite number of atoms. The size of the nano-island is in the order of nano-scale in the plane and z-direction. It is known as "man-made atom". Compared with other magnetic materials, nano-islands can significantly increase the specific surface area, mainly in magnetic storage devices, small structure and high coverage solar cells, lithium-ion batteries and photodetectors and other potential applications. Therefore, the theoretical study of magnetic nanisland has important guiding significance for its application. In this paper, the physical properties of hexagonal magnetic nanisland are studied based on the correlation effective field theory. In this paper, the effects of physical parameters on magnetic moment, susceptibility, phase transition temperature, hysteresis loop, ladder effect, internal energy and specific heat of magnetic nanisland are studied. The results show that when the exchange coupling is changed, the magnetocrystalline anisotropy and transverse field will occur, and there will be two phase transition points and one compensation point at the same time in a certain parameter range. With the change of each parameter, the inflexion point will appear in different positions, that is, the phase transition temperature is different, and the specific heat curve will appear strange phenomenon at the phase transition temperature, which is a typical second-order phase transition characteristic. When the system is in low temperature, the magnetic moment shows obvious ladder effect under the action of external field, and the surface exchange action and magnetocrystalline anisotropy have an important influence on the ladder effect. Exchange coupling, magnetocrystalline anisotropy, transverse field and temperature all affect the number and shape of hysteresis loops. Based on the correlation effective field theory, the physical properties of cubic magnetic nanisland are also studied. The magnetic moment, phase transition temperature and ladder effect of the cubic island are greatly affected by the magnetocrystalline anisotropy of the nucleus. Similar to that of the hexagonal structure, there are many phase transition points in the system within a certain range of parameters. The variation trend of internal energy and specific heat curve is similar to that of hexagonal structure nano-island. At low temperature, magnetic moment ladder and multi-loop hysteresis loop appear in the system.
【学位授予单位】：沈阳工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB383.1

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