【作者】 文岐业；

【导师】 张怀武；

【作者基本信息】 电子科技大学 ， 材料物理与化学， 2005， 博士

【摘要】 电子是电荷的载体,同时又是自旋的载体。利用电子“电荷”实现了半导体技术的革命,而利用电子“自旋”正在实现信息存储领域的新一次革命。随着巨磁电阻磁头、磁性随机存储器(MRAM)、自旋晶体管等自旋电子器件在重大基础理论和应用技术上的突破,自旋电子学的理论和应用研究成为当前电子学与信息技术领域的热点。其中基于巨磁阻效应(GMR)的MRAM以其非挥发性、高速读取和低能耗的特点而有望成为下一代通用存储器,因而是信息存储领域最具吸引力的研究方向之一。 两个磁性层被一个非磁性层隔开而成的“铁磁层/非磁层/铁磁层”磁三明治结构,是实现MRAM器件最核心的组件。为了适应MRAM器件大存储密度的需要,磁三明治单元在长宽尺寸上向深亚微米发展,在厚度上则仅为几十纳米。在这样小的尺寸下,磁三明治单元层间静磁耦合效应和边缘退磁场显著增强,引起自旋电子输运特性的深刻变化从而对器件应用产生影响:其次,微小单元磁畴结构和磁化翻转机制也会出现变化,可能引起单元均匀性变差、读写误操作和能耗的增加。最后,界面粗糙度、层间原子扩散等微结构缺陷的存在对器件稳定性的影响也变得明显。这些问题,已经制约了MRAM器件的进一步发展。 本论文正是针对以上问题,在深入分析其内在物理机制的基础上,以磁三明治材料为主要研究对象,在基础理论、实验仿真、材料和工艺上都作了探索性和创新性研究,主要内容为: (1)深入分析了纳米磁性多层膜中自旋电子输运的唯象理论模型。通过对边界条件的调整,计算了耦合型磁性多层膜巨磁阻系数随非磁性隔离层厚度的振荡变化,得到了与实验一致的结果。推导了磁三明治材料巨磁阻效应唯象理论五层模型,计算了GMR效应与界面不对称散射因子(Ns)和电子平均自由程(λ)的关系。首次在理论上解释了界面自旋相关散射强、电子平均自由程短的非晶薄膜可以使磁三明治材料以极薄的磁性层获得相对较大的巨磁阻效应。 (2)应有有限元微磁学方法,模拟了亚微米单层薄膜椭圆型单元的长宽比、薄膜厚度对其磁化翻转行为的影响,得到与实验观察一致的结果。基于MRAM器件中电流线提供的非均匀磁场,研究了深亚微米尺度磁三明治单元的磁化翻转行为。结果表明,无论是单层膜还是磁三明治,其磁化翻转模式都强烈依赖于单元的长宽比R和薄膜厚度。对磁三明治单元,应该选择相对较大的长宽比以得到单一稳定的磁化翻转模式,但是R值过大将会导致翻转场过大。而较薄的磁性层(<10nm)既可以降低薄膜的静磁能从而减小对周围单元的干扰,又可以得到单一的翻转模式而提高器件操作的稳定性,因而可以有效提高MRAM的磁化翻转特性和存储密度。更多还原

【Abstract】 An electron is the carrier of both "charge" and "spin". With the dawn of the new millennium has emerged a novel technology which exploits electron spin and uses it to differentiate electrical carriers into two different types according to their spin directions. As the spin-electronics (spintronics) devices such as magnetic hard disk drive (HDD), spin transistor and magnetic random access memory (MRAM) were commercial used or developed as prototypes, spintronics becomes one of the most rapidly expanding fields in basic research and industrial application.MRAM has the advantages of nonvolatility, fast write and read times and low power consumption, and is potentially to be the memory standard. Magnetic sandwich with two ferromagnetic layers (FM) separated by a nonferromangtic layer (NM), is the key element of MRAM. When magnetic sandwich scales down to micrometer or sub-micrometer for the purpose of increase the recording density, its application characteristics changes profoundly. These includes: (a) The internal demagnetizing-field and magnetostatic coupling between magnetic layers increase significantly, which affect the transport properties of spin electrons; (b) The stability of the domains structure and the reversal characteristics of the memory cell will be worsen. In additional, the roughness and atomic interdiffusion between the layers will also cripple the GMR effect and application characteristics.In this thesis, the basic physical mechanisms of the aforementioned issues have been firstly analyzed. Then basic theory, experimental simulation, new materials and technologies have been explored and investigated based on the magnetic sandwich.Following are the main results:(1) The Camely-Barnas phenomenological theory is extended to study the magnetic sandwiches. The effects of interfacial spin-dependent-scattering-asymmetrical factor (Ns), and the electronic-mean-free path (X) on GMR ratio are calculated. The results show that large Ns and small X are helpful to obtain large GMR with thinner thickness of FM. Therefore, the Co-basis amorphous soft-magnetic films, which possess high spin polarization and short X, can be use to spin-valve sandwich to obtain larger GMR with small thickness.(2) The reversal processes of single magnetic dots and MRAM cell have been studied with finite element micromagnetic simulations. The simulation results of magnetic dots agree with the experimental results very well thus confirms the reliability and effectiveness of micromagnetic method. Under the nonuniform magnetic field更多还原