磁随机存储器根据写入方式的不同分为STT-MRAM和SOT-MRAM两种类型。STT-MRAM已接近量产而SOT-MRAM在应用中还面临着一个关键性问题，即如何实现无外加磁场下的SOT驱动磁翻转。目前，关于无外磁场SOT磁翻转的研究主要集中在基础原理和单铁磁层器件方面，而在SOT-MRAM的核心存储结构磁性隧道结（MTJ）中，无外场SOT翻转尚未能实现。这主要是因为目前的无外场SOT翻转的物理机理或器件结构无法在保证MTJ性能的前提下应用到MTJ结构中。本项目拟基于通用的MTJ结构和材料，在保持MTJ性能的前提下，通过电压调控或增强界面SOT效应来实现MTJ的无外场SOT翻转。通过研究电压调控下，MTJ的垂直磁各向异性、SOT诱导的等效场、自由层磁化强度的瞬时变化量以及层间耦合场等方面来揭示SOT驱动的磁翻转在电压调控下的翻转过程和背后的物理机制，从原理和器件两方面实现MTJ的无外场翻转。

Based on writing process, MRAM can be classified into STT-MRAM and SOT-MRAM. The former has been reported to be mass production recently, while the latter is still struggling against some fundamental issues in applications. For example, one big challenge of practical SOT-MRAM is eliminating the applied external magnetic field during SOT-driven magnetic switching. Currently, most researches on the field-free SOT switching focus on simple SOT structures with a single ferromagnetic layer, not the magnetic tunnel junctions (MTJs), which are the core cell structure of SOT-MRAM. More importantly, these reported field-free switching solutions cannot be used in a MTJ structure while maintaining its high performance. This proposal will seek a MTJ-compatible field-free switching solution through voltage control effects or by introducing enhanced interfacial SOT effects. The important parameters during SOT switching, such as perpendicular magnetic anisotropy, SOT effective fields, and magnetic dynamics under voltage control as well as interlayer coupling in a MTJ structure will be characterized to investigate field-free switching of MTJ structures from both physical mechanism and device level.