低维磁性结构中磁振子激发、传播和衰减物理机制的研究

Magnons are collective excitations of the spin structure in magnetic materials, these can propagate through the solid without dissipation. The great advantages of magnon devices are low energy costs, high integration and ultrafast, however before entering the utility, many aspects remains unclear, for instance, how magnons be excited and propagate through the different low dimensional magnetic structures, and how to increase the lifetime of magnons and so on. In this study we will investigate the physical mechanism of magnon dynamics in various low dimensional magnetic structures, and try to find the solution of improving the lifetime of magnons. Firstly the various magnetic microstructures will be fabricated by Molecular Beam Epitaxy and micro fabrications. Secondly the magnon excitations and propagation will be investigated by Ferromagnetic resonance and High resolution electron energy loss spectroscopy, specifically by choosing FeRh as the research candidate, we will investigate the phase transition and temperature effect on the magnon dynamics. By investigating FeMn/Co, we try to find that how the antiferromagnetic exchange interaction and exchange bias influence magnon excitations, also we will quantify the dimension and size effect on magnon dynamics. And we will replace the metal substrate with insulating one, try to minimize the hybridization effect and increase the lifetime of magnons. Finally, the intrinsic mechanism of magnon dynamics in low decisional magnetic structures will be understand and the method of controlling magnon excitations and long lifetime magnons will be realized.

磁振子是磁性介质中自旋的集体激发，可以低耗散、长距离的传播。未来基于磁振子的器件具备低能耗、高集成度和超快等独特优点。但是实用之前，还有许多基本问题没有解决，包括磁振子在各种低维磁性结构中是如何激发和传播的，以及如何提高磁振子寿命等。本项目将深入研究各种低维磁性结构中磁振子动力学行为的物理机制以及提高磁振子寿命的方法。首先，利用超高真空分子束外延和微纳米加工制备各种低维磁性结构，然后采用铁磁共振和高分辨电子能量损失谱测量其磁振子的激发和传播，选择FeRh合金薄膜，通过变温实验测量温度和相变对磁振子激发的影响，选择FeMn/Co体系研究交换耦合和交换偏置与磁振子之间的关联，制备不同维度和尺寸的样品研究磁振子激发的尺寸效应，通过绝缘衬底消除电子杂化效应，抑制磁振子衰减，提高磁振子寿命，深入理解磁振子在各种低维磁性结构中激发和传播和衰减的物理机制，最终控制磁振子激发行为和提高磁振子寿命。

低维磁性结构中磁振子的激发、传播和寿命是当前自旋电子学领域的前沿研究课题之一，在低功耗超快信息存储领域具有极其重要的科学和应用价值。我们利用自旋泵浦铁磁共振，电致发光，电子顺磁共振和自旋塞贝克效应等研究了铁磁绝缘体/非磁（FMI/NM）以及反铁磁绝缘体（AFMI）中磁振子激发对于自旋流的影响及其相关物理机制。(1) 对YIG/Pt体系中磁振子相关的物理现象进行了研究，微波可以激发YIG中的磁振子，产生自旋流进入Pt层，利用逆自旋霍尔效应检测出来，但是利用自旋塞贝克效应却无法激发磁振子产生自旋流，我们认为由于ITO和YIG的热导率几乎相同，或者界面自旋混合电导呈现较大的负温度系数导致的。（2）研究了拓扑绝缘体对铁磁绝缘体各向异性的影响，采用电子顺磁共振激发TIG中的磁振子，进而使TIG中自旋和Bi2Se3的表面态产生耦合，表面态电子通过类似RKKY的相互作用参与了TIG中Fe3+之间的交换耦合增强了TIG的各向异性能，而Bi2Se3的体态电子则减弱了TIG的垂直各向异性。（3）反铁磁绝缘体NiO薄膜中的电致发光，我们的实验证实了阻态翻转过程中电致发光的确来源于NiO中杂质能级上电子的退激发而非热效应，提供了一种非破坏性研究低功耗电致电阻效应的方法，同时提供了改进NiO单极性翻转稳定性的方法。（4）我们还设计了一种基于非磁性/磁性双层膜（Pd/YIG）结构的光斑均匀性探测器件，利用逆自旋霍尔电压与外磁场之间的斜率因子可以灵敏地探测出局域的温度梯度值、 光斑均匀性及外磁场的方向。