Role of an in-plane ferromagnet in a T-type structure for field-free magnetization switching
Role of an in-plane ferromagnet in a T-type structure for field-free magnetization switching
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DOI：
10.1063/5.0079400
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发表时间：
2022-03
影响因子：
4
通讯作者：
W. L. Yang;Z. R. Yan;Y. Xing;C. Cheng;C. Guo;X. M. Luo;M. K. Zhao;G. Yu;C. Wan;
中科院分区：
文献类型：
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作者：
W. L. Yang;Z. R. Yan;Y. Xing;C. Cheng;C. Guo;X. M. Luo;M. K. Zhao;G. Yu;C. Wan;
无外加磁场的电流感应自旋轨道扭矩(SOT)驱动的确定性磁化开关在磁随机存取存储器中具有潜在的应用前景。在这里，我们实现了T型结构(CoFeB/W/CoFeB)的无场磁化转换，其中两个CoFeB层分别具有垂直磁各向异性和面内磁各向异性(IMA)。我们发现对称性破缺磁场的方向与底层CoFeb(IMA)的磁化强度是平行的，这不能用这一层的杂散场来解释。此外，通过在底层CoFeB和W层(CoFeB/MgO/W/CoFeb)之间放置2.5 nm厚的MgO绝缘层来阻挡层间交换耦合和来自底部CoFeb的自旋电流，仍然实现了无场SOT开关，这主要是由于我们的器件中的Néel橙皮效应。通过微磁模拟，在模型中引入埃量级的粗糙度来计算对称破缺磁场，定性地与实验结果相吻合。此外，我们还用电流诱导磁滞回线移位的方法得到了CoFeB的自旋霍尔角([公式：见正文]=−0.024)，在电流诱导的SOT开关过程中，来自底层CoFeB的有效效率χ的贡献约占总贡献的26%。这些结果表明，T型结构中的面内铁磁层不仅为SOT的无场磁化转变提供了对称性破缺磁场，而且还提供了自旋电流。
Deterministic magnetization switching driven by current-induced spin–orbit torque (SOT) without an external magnetic field has potential applications in magnetic random access memory. Here, we realized the field-free magnetization switching in a T-type structure (CoFeB/W/CoFeB), where the two CoFeB layers have perpendicular magnetic anisotropy and in-plane magnetic anisotropy (IMA), respectively. We discovered that the direction of symmetry-breaking field is parallel to the magnetization of the bottom CoFeB (IMA), which cannot be explained by a stray field of this layer. In addition, by placing a 2.5-nm thick insulating layer of MgO between the bottom CoFeB and W layer (CoFeB/MgO/W/CoFeB) to block the interlayer exchange coupling and the spin current from the bottom CoFeB, the field-free SOT switching was still achieved, primarily due to the Néel orange-peel effect in our devices. By using micromagnetic simulations, the roughness of angstrom magnitude was introduced into the model to calculate the symmetry-breaking field, finding a qualitative agreement with experiments. Moreover, we obtained the spin Hall angle of CoFeB ([Formula: see text] = −0.024) by the current-induced hysteresis loop shift method, and the contribution of the effective efficiency χ from the bottom CoFeB was accounted for about 26% of the total in the current-induced SOT switching process. These results indicated that an in-plane ferromagnet layer in the T-type structure provides not only the symmetry-breaking field but also spin current for the field-free SOT magnetization switching.