兰州大学机构库 >物理科学与技术学院
隧道结中自旋动力学的微磁学研究
Alternative TitleMicromagnetic Studies of Spin Dynamics in Magnetic Tunnel Junction
刘先印
Thesis Advisor王建波
2015-05-27
Degree Grantor兰州大学
Place of Conferral兰州
Degree Name硕士
Keyword360°畴壁 2π-vortex 自旋转移矩 微磁学模拟
Abstract近年来,巨磁电阻效应、隧道磁电阻效应和自旋转移矩效应越来越受到人们关注。利用微纳加工技术可以应用这些效应制作磁性随机存储器、赛道存储器以及自旋纳米振荡器等磁性纳米器件。本文利用微磁学模拟的方法研究了在自旋转移矩驱动下隧道结的磁化动力学过程。 研究了垂直注入极化电流驱动360°畴壁运动的情况。在不同参数的情况下,计算了360°畴壁运动速度的影响因素,接着从唯象模型和一维模型推导了360° 畴壁在极化电流驱动下运动,最后通过局域注入极化电流方式实现了操作单个360°畴壁运动而不影响其他360°畴壁的目的;并模拟了存在钉扎的纳米带中,360°畴壁的极限密度。 引入Dzyaloshinskii–Moriya 相互作用后,纳米圆盘可能会出现一种新型的磁化结构分布2π-vortex。我们利用微磁学模拟了2π-vortex 存在的条件。接着在直径为140 纳米的圆盘中,研究了极化电流驱动2π-vortex 的运动。结果显示当纳米圆盘的直径和注入自旋极化电流的区域匹配时,2π-vortex 可以稳定进动,并且2π-vortex 的进动很快就能达到稳定状态,频率和电流密度呈线性正比关系,这为自旋纳米振荡器提供了一个新的思路。 利用微磁学模拟了隧道结自由层在引入磁晶各向异性后,自由层的自然共振频率和微波辅助自由层磁化翻转的过程。
Other AbstractIn recent years, giant magnetoresistance (GMR), tunnel magnetorestance (TMR) and spin transfer torque (STT) effect have attracted considerable attention since they have potential applications in the magnetic random access memory,racetrack memory and microwave oscillators. In this thesis, we investigated Spin Dynamics in magnetic tunnel junction via micromagnetic simulations. The main contents are as follows: The 360°domain wall motion driven by current perpendicular to the magnetic plane was simulated. The dependences of 360°domain wall velocity on the current density with different parameters are shown, and the difference between Slonczewski torque effect and fieldlike torque is analyzed in detail. The behaviors of 360°domain wall are shown by Lagrangian formalism. In addition, we provide a new type of current perpendicular to the magnetic plane magnetic tunnel junction with many 360°domain walls, which is designed to achieve local current, for driving the single 360° domain wall. The local spin polarized current introduced can drive single 360°domain wall. For magnetic system, the introduction of Dzyaloshinskii-Moriya interaction (DMI) can lead to curious phenomena. A new type of skyrmion-like spin texture, 2π-vortex is obtained in a thin nano-disk with Dzyaloshinskii-Moriya interaction. We have simulated the existence of 2π-vortex by energy minimization method. Furthermore, the spin polarized current is introduced in order to drive the motion of 2π-vortex in a nano-disk with diameter 140 nm. When the current density matches with the current injection area, 2π-vortex soon reaches a stable precession. The relationship between the precession frequency of 2π-vortex and the current density is almost linear. In a magnetic tunnel junction, a free layer with in-plane magnetic anisotropy exhibits a higher stability. We have investigated magnetization reversal of magnetic tunnel junction with different magnetic anisotropies assisted by microwave field. Simulations show that natural ferromagnetic resonance frequency increases with the increasing magnetic anisotropy constant. The critical current density of the magnetization switch can be reduced in the memory cell with in-plane magnetic anisotropy by microwave assistance. The magnetization switching mechanism shows some new features due to the introduction of in-plane magnetic anisotropy.
URL查看原文
Language中文
Document Type学位论文
Identifierhttps://ir.lzu.edu.cn/handle/262010/229327
Collection物理科学与技术学院
Recommended Citation
GB/T 7714
刘先印. 隧道结中自旋动力学的微磁学研究[D]. 兰州. 兰州大学,2015.
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