钴镁氧颗粒膜的磁学性质研究

发布时间：2018-05-21 18:26

本文选题：钴镁 + 颗粒　；参考：《南京大学》2014年博士论文

【摘要】：近年来,随着科学技术的发展,人们要求提高信息存储密度,缩小存储器件尺寸。存储器件中磁性颗粒的尺寸缩小,有利于提高存储密度,但是当磁性颗粒的大小逐渐减小到临界值以下时,磁性颗粒内的磁矩会变得无序,这就是所谓的"超顺磁性限制",因此,找到有效稳定磁矩的办法,这对于基础研究和技术应用都很有意义。引入交换偏置效应是解决这个问题的可能办法之一。1956年,Meikleijohn和Bean在部分被氧化的Co颗粒系统中观察到交换偏置效应。此后,交换偏置效应在多种人造材料中被观察到,科学家们对交换偏置现象做了很多深入的探索。2003年,Shumryev等在《Nature》上撰文提出,可以利用Co/CoO颗粒中的交换偏置效应打破纳米Co颗粒的超顺磁性限制,提高Co颗粒的热稳定性,并且增大矫顽力。这一研究成果为交换偏置效应带来了新的应用价值,因此引起了人们的广泛兴趣。弄清交换偏置效应产生的微观机制并用恰当的理论加以解释,再据此设计制造能获得高交换偏置场的人造材料,是目前这一领域的研究重点。但是令人遗憾的是迄今为止交换偏置效应产生的确切微观机制仍然不明确,已有的多种理论模型也仍然存在争议。有一种理论认为交换偏置效应与铁磁和反铁磁界面的自旋结构有关,在铁磁和反铁磁界面处不随外加磁场旋转的未补偿自旋是交换偏置效应的真正来源,交换偏置场的大小与这种未补偿自旋的密度高低有关。目前,这种观点被比较广泛地接受,并且正在被越来越多的实验结果证实。根据交换偏置效应的特征,结合磁性颗粒膜的性质,我们制备了一系列Co/CoO-MgO颗粒膜样品(Co/CoO颗粒嵌入MgO介质)。本文研究的重点:1.利用磁性表征技术测量这一系列Co/CoO-MgO颗粒膜样品的磁、电参数(交换偏置场、矫顽力、磁畴结构、电阻等);2.利用X射线磁性圆二色性(XMCD)实验确定Co与CoO界面处的自旋结构;3.根据实验结果探究该系统具有大交换偏置场和大矫顽力的原因,证明交换偏置的未补偿自旋模型理论的合理性;4.明确交换偏置场和矫顽力之间的关系,找到调控交换偏置场和矫顽力的可能途径,以利于研发高性能的磁记录材料。5.测试发现样品具有显著的磁光效应增强,这是样品中的金属钴颗粒表面的局域表面等离激元共振引起的。论文主要包括以下三个部分:一、(Co/CoO)-MgO颗粒膜中的交换偏置效应的研究1、利用磁控溅射技术制作了一系列组份不同的Co/CoO-MgO颗粒膜样品。选取钴原子比为69%的样品Co69Mg7024(即CCMO1)和钻原子比为80%的样品Co80Mg6014(即CCM02)做了仔细的研究。2、在渗流阈值以下的样品CCMO1中观察到高达2460Oe的交换偏置场和高达62000e的矫顽力。在Co的L2,3测得的x射线磁圆二色性吸收谱清楚地表明铁磁信号部分来源于通常呈反铁磁性的CoO壳层。3、研究结果证实了未补偿自旋模型的正确性,而且进一步证实了被钉轧的未补偿自旋的数量影响交换偏置场,可旋转的未补偿自旋的数量影响矫顽力。我们观察到的来源于反铁磁CoO壳层的铁磁XMCD信号就清楚地证明了后者的存在。二、(Co/CoO)-MgO颗粒膜中的巨矫顽力研究1、借助于高分辨透射电子显微镜(HRTEM)图片,我们清楚地确定了样品Co56/(CoO)32-(MgO)12和 Co75/(CoO)15-(MgO)10 的形态和结构。2、借助于原子力显微镜(AFM)和磁力显微镜(MFM)技术,我们弄清了样品Co56/(CoO)32-(MgO)12和 Co75/(CoO)15-(MgO)10的形貌和畴结构,并进行了对比。3、通过分析Co/CoO-MgO纳米颗粒膜样品的磁滞回线,我们得到了样品Co56/(CoO)32-(MgO)12和Co75/(CoO)15-(MgO)10在相同条件下交换偏置场和矫顽力之间的差异,以及两个样品交换偏置场和矫顽力随温度变化的情况。我们还特别测量了外加不同大小冷却磁场时样品Co56/(CoO)32-(MgO)12的交换偏置场和矫顽力。4、通过对样品Co56/(CoO)32-(MgO)12和Co75/(CoO)15-(MgO)10的磁性分析可得,钴体积比恰好达到渗流阈值的样品Co56/(CoO)32-(MgO)12具有高达7121 Oe的矫顽力和高达3435 Oe的交换偏置场。可见交换偏置的存在有利于提高系统的矫顽力。5、研究结果表明,通过改变Co/CoO-MgO纳米颗粒的交换偏置场的大小可以调控其矫顽力。三、(Co/CoO)-MgO颗粒膜中的克尔效应研究1、测量得出Co/CoO-MgO颗粒膜的磁光克尔角与入射光波长之间的关系曲线。应用经典4×4矩阵法拟合了Co/CoO-MgO颗粒膜的磁光克尔角与入射光波长之间关系的实验曲线。2、测量了入射光波长为共振波长时所有样品的磁光克尔角。3、用等离激元理论解释了样品中磁光克尔角增大的原因。
[Abstract]:In recent years, with the development of science and technology, people need to improve the density of the information storage and reduce the size of the memory parts. The size of the magnetic particles in the memory parts is reduced, which is beneficial to the increase of the storage density. But when the size of the magnetic particles gradually decreases below the critical value, the magnetic moments in the magnetic particles will become disordered. This is called "super". Paramagnetic confinement, therefore, it is significant for both basic and technical applications to find effective stable magnetic moments. The introduction of the exchange bias effect is one of the possible solutions to this problem in.1956, and Meikleijohn and Bean observe the exchange bias effect in the partially oxidized Co particle system. A variety of artificial materials have been observed, scientists have made a lot of in-depth exploration on the phenomenon of exchange bias in.2003 years. Shumryev and other articles on suggest that the exchange bias effect in Co/CoO particles can be used to break the superparamagnetic limit of nano Co particles, improve the thermal stability of Co particles, and increase the coercivity. Because of its new application value for the exchange bias effect, it has aroused wide interest. It is a major focus in this field to make clear the microscopic mechanism of the exchange bias effect and to explain it with appropriate theory, and then to design and manufacture artificial materials that can obtain high exchange bias field. So far the exact microscopic mechanism of the exchange bias effect is still unclear, and many theoretical models are still controversial. One theory is that the exchange bias effect is related to the spin structure of the ferromagnetic and antiferromagnetic interfaces, and the uncompensated spin at the ferromagnetic and antiferromagnetic interfaces that do not rotate with the magnetic field is the exchange bias effect. The real source, the size of the exchange bias field is related to the density of this uncompensated spin. At present, this view is widely accepted and is being confirmed by more and more experimental results. Based on the characteristics of the exchange bias effect and the properties of magnetic granular films, we have prepared a series of Co/CoO-MgO granular film samples (Co/Co O particles are embedded in the MgO medium. The focus of this paper is: 1. using magnetic characterization techniques to measure the magnetic, electrical parameters (exchange bias field, coercive force, domain structure, resistance and so on) of this series of Co/CoO-MgO particles; 2. using X ray magnetic circle two color (XMCD) experiment to determine the spin structure at the interface between Co and CoO; 3. explore the system based on the experimental results. The reasons for the large exchange bias field and the large coercivity are proved, and the reasonableness of the theory of the uncompensated spin model for the exchange bias is proved. 4. the relationship between the exchange bias field and the coercive force is clearly defined, and the possible way to regulate the exchange bias field and coercive force is found to facilitate the development of the high performance magnetic recording material.5. test discovery sample. The magneto optic effect is enhanced, which is caused by the local surface plasmon resonance on the surface of the metal cobalt particles in the sample. The thesis mainly includes the following three parts: (1) a study of the exchange bias effect in (Co/CoO) -MgO granular film. A series of different Co/CoO-MgO particle films were fabricated by magnetron sputtering. A careful study of the 69% sample Co69Mg7024 (CCMO1) and the sample Co80Mg6014 (CCM02) of the drill atomic ratio (CCM02) was carefully studied. The exchange bias field of up to 2460Oe and the coercive force of up to 62000e were observed in the sample CCMO1 below the threshold of the percolation threshold. The ferromagnetic signal part of the X ray magnetic circle two color absorption spectrum measured in Co L2,3 was clear. The results from the CoO shell.3, usually antiferromagnetic, confirm the correctness of the uncompensated spin model and further confirm the effect of the number of uncompensated spins on the exchange bias field, and the number of rotatable uncompensated spin affects the coercive force. The ferromagnetic XMCD signal from the antiferromagnetic CoO shell is observed. The existence of the latter is clearly demonstrated. Two, the giant coercive force in the granular film of (Co/CoO) -MgO is 1. With the help of high resolution transmission electron microscopy (HRTEM) images, we have clearly identified the morphology and structure.2 of the samples Co56/ (CoO) 32- (MgO) 12 and Co75/ (CoO) 15- (MgO) 10, with the aid of atomic force microscopy and magnetic force microscopy. We have made clear the morphology and domain structure of the samples Co56/ (CoO) 32- (MgO) 12 and Co75/ (CoO) 15- (MgO) 10, and compared the.3. By analyzing the hysteresis loop of the Co/CoO-MgO nanoparticle film samples, we obtained the difference between the exchange bias field and the coercive force of the sample Co56/ (CoO) 12 and 10. We also measured the exchange bias field and coercive force.4 of the sample Co56/ (CoO) 32- (MgO) 12 added with different sizes of cooling magnetic field, and the cobalt volume ratio was right to the percolation threshold by the magnetic analysis of the sample Co56/ (CoO) 32- (MgO) 12 and Co75/ (CoO) 15- (MgO) 10. The sample Co56/ (CoO) 32- (MgO) 12 has a coercivity of up to 7121 Oe and a exchange bias field with up to 3435 Oe. The existence of the exchange bias is beneficial to improve the coercive force.5 of the system. The results show that the coercive force can be regulated by changing the exchange bias field of Co/CoO-MgO nanoparticles. The Kerr in three, (Co/CoO) -MgO particle film can be controlled. The relationship between the magneto-optical Kerr angle of the Co/CoO-MgO particle film and the wavelength of the incident light is measured. The experimental curve.2 of the relation between the magnetic light Kerr angle of the Co/CoO-MgO particle film and the incident light wavelength is fitted by the classical 4 x 4 matrix method. The magneto-optical Kerr angle.3 of all samples when the incident light wave length is the resonant wavelength is measured. The reason for the increase of the magneto optical Kerr angle in the sample is explained by the plasmon theory.
【学位授予单位】：南京大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：O484.43

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