铁磁金属FeCo合金纳米结构中自旋驻波阻尼和磁散射的研究

The study of spin waves with nonzero wavevector has attracted a lot of attentions in the last decades since it can drastically reduce the power consumption of spintronics devices when using it as the carrier of information processing. In order to get a long lifetime of spin waves, exploring its damping is a key issue for the application of magnonic devices. Recent theoretical studies have revealed that the standing spin waves will have an additional damping. This damping is square wave-number dependent duo to the exchange interaction introduced by its nonlinear spin configuration. However, the results of the experimental works in standing spin waves is inconsistent with the predication. What’s more, the experimental results indicated that the scattering between the standing spin waves and uniform mode maybe enhance or suppress the damping of uniform mode. The physical mechanism inside them is still unknown. In this project we will study the damping of uniform mode and standing spin waves and the scattering between them in the FeCo alloy nanostructures by FMR and TRMOKE. We will fabricate the FeCo alloy thin film and its nanostructures with periodic modulation of thickness. After that we will explore the damping of FeCo nanostructures by conventional FMR in frequency domain and TRMOKE in time domain. We will develop two sources FMR and use two microwave sources to excite the uniform mode and standing spin waves simultaneously, and observe the scatting between standing spin waves and uniform mode through measuring the damping constant of uniform mode as the function of microwave power of standing spin waves. To explore the physical mechanism of the damping of standing spin waves and the scattering between the standing spin waves and uniform mode will help us to seek the new materials and structures for the application of magnonic devices.

以自旋波作载体的信息处理具有低功耗、非易失性等优点，使得关于自旋波的研究成为研究热点。自旋波器件实用化的要求希望获得长寿命的自旋波，为此开展自旋波阻尼机理的研究十分重要。最近理论研究考虑了自旋波中自旋非共线而引入的交换作用，发现自旋波会额外增加一个和波数平方相关的阻尼项，但是实验结果和理论预测相差甚远。实验结果还看到自旋驻波的出现会增强或是减少一致进动的阻尼，其物理机理还不是很清楚。为此，本项目我们将在FeCo合金纳米结构中采用频率测量的铁磁共振FMR和时域测量的时间分辨磁光克尔仪TRMOKE研究其一致进动和自旋驻波的阻尼。为了研究一致进动和自旋驻波间的磁散射，我们将发展双微波源铁磁共振技术，采用双微波源同时激发一致进动和自旋驻波，通过自旋驻波激发功率的大小来控制自旋波的密度，通过一致进动线宽的变化来研究两者磁散射的大小和可能的物理机制。本研究对自旋波器件的设计和应用有重要参考价值。

以自旋波作载体的信息处理具有低功耗、非易失性等优点，使得关于自旋波的研究成为研究热点。自旋波器件实用化的要求希望获得长寿命的自旋波，为此开展自旋波阻尼机理的研究十分重要。最近研究表明磁子-磁子相互作用和散射对阻尼有影响，特别是双磁子间的相互作用和散射能够增强或是抑制阻尼。本项目我们首先发展了双微波源铁磁共振技术。在该技术中，我们采用两个微波源同时激励材料中两个具有不同频率自旋波，这有助于我们开展两个磁子间的相互作用和散射的研究。接着我们生长了低阻尼的FeCo和CoFeB合金薄膜。利用铁磁共振我们研究了CoFeB薄膜中的一致进动和自旋驻波的阻尼。自旋驻波的阻尼要小于一致进动，这是由于自旋驻波发生双磁子散射的几率降低导致。接着我们采用铁磁共振和时间分辨磁光克尔仪研究了基于CoFeB的人工反铁磁体系中的磁子-磁子相互作用和阻尼。我们发现两层薄膜间的动力学耦合会增强光学支并压制声学支的阻尼。我们同时发现两层磁矩间的对称性破缺会导致磁子-磁子耦合，进而能够让声学支和光学支两种磁子产生杂化。我们从理论和实验两方面证实不对称结构可以实现人工反铁磁中磁子-磁子耦合大小的调控。本研究探究两个磁子间的相互作用和散射的物理过程对理解阻尼的物理机理和对低阻尼自旋波器件应用有重要参考价值。