【摘要】：低維納米材料是當(dāng)前科學(xué)研究的熱點(diǎn)之一,低維納米材料包括二維、一維和零維納米材料。其中零維納米材料在材料結(jié)構(gòu)上可以表現(xiàn)為量子點(diǎn)、納米島等。納米島是由有限數(shù)目的原子構(gòu)成,在x-y平面及z方向上的尺寸均在納米量級(jí),被譽(yù)為是“人造原子”。納米島與其它磁性材料相比可以顯著地提高比表面積,主要在磁儲(chǔ)備裝置、小結(jié)構(gòu)高覆蓋率太陽(yáng)能電池、鋰離子電池和光電探測(cè)器等有潛在的應(yīng)用前景。因此,磁性納米島的理論研究對(duì)其應(yīng)用有重要的指導(dǎo)意義。本文基于相關(guān)有效場(chǎng)理論研究了六角磁性納米島的物理特性。論文中,主要研究了各物理參數(shù)對(duì)磁性納米島的磁矩、磁化率、相變溫度、磁滯回線(xiàn)、階梯效應(yīng)、內(nèi)能、比熱的影響。結(jié)果顯示,改變交換耦合作用、磁晶各向異性和橫場(chǎng)時(shí),系統(tǒng)會(huì)出現(xiàn)重入現(xiàn)象,并且在一定參數(shù)范圍內(nèi),系統(tǒng)會(huì)同時(shí)出現(xiàn)兩個(gè)相變點(diǎn)和一個(gè)補(bǔ)償點(diǎn);隨著各參數(shù)的變化,系統(tǒng)內(nèi)能曲線(xiàn)會(huì)在不同的位置出現(xiàn)拐點(diǎn),即相變溫度不同;比熱曲線(xiàn)在相變溫度處會(huì)出現(xiàn)奇異現(xiàn)象,這是典型的二級(jí)相變特點(diǎn);當(dāng)系統(tǒng)處于低溫時(shí),在外場(chǎng)的作用下,磁矩表現(xiàn)出明顯的階梯效應(yīng),表面交換作用和磁晶各向異性對(duì)階梯效應(yīng)有重要影響;交換耦合作用、磁晶各向異性、橫場(chǎng)及溫度都會(huì)影響系統(tǒng)磁滯回線(xiàn)的環(huán)數(shù)及形狀�；谙嚓P(guān)有效場(chǎng)理論還研究了立方結(jié)構(gòu)磁性納米島的物理特性。立方結(jié)構(gòu)納米島的磁矩、相變溫度及階梯效應(yīng)受核的磁晶各向異性影響較大。與六角結(jié)構(gòu)納米島的變化規(guī)律類(lèi)似,在一定的參數(shù)范圍內(nèi),系統(tǒng)也出現(xiàn)了多個(gè)相變點(diǎn)。內(nèi)能、比熱曲線(xiàn)的變化趨勢(shì)與六角結(jié)構(gòu)納米島相似。在低溫時(shí),系統(tǒng)出現(xiàn)了磁矩階梯和多環(huán)的磁滯回線(xiàn)。
[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.
【學(xué)位授予單位】：沈陽(yáng)工業(yè)大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類(lèi)號(hào)】：TB383.1

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本文編號(hào)：2444229