可重构的磁构型磁子晶体及其动态调控

Recently, the investigation of the magnonic crystal with periodic variation of geometric or material parameters has been advanced greatly. However, the geometry- or material-modulated magnonic crystals are less reconfigurable and hard to realize dynamical manipulation, especially ultrafast manipulation. The reconfiguration and dynamical manipulation are essential for designing fast programmable magnonic devices. In this project, we propose a new type of magnonic crystal, magnetic texture-modulated magnonic crystal consisting of periodically distributed magnetic structures. As the magnetic structure can be changed by magnetic field or spin-transfer (or spin-orbit) torque and the relaxation time of magnetization configuration is in the nanosecond scale, the magnetic texture-modulated magnonic crystals are reconfigurable and can be manipulated ultrafastly. Theoretically, based on the micromagnetics, we will study the generation of some of the magnetic texture-modulated magnonic crystals such as domain wall and skyrmion magnonic crystals, the spin wave propagation and their dynamical manipulation. Experimentally, by using molecular-beam epitaxy, magnetron sputtering and nano-processing technology, we will fabricate nanostrip domain-wall magnonic crystals. We will further measure their magnetic dynamic properties, spin wave propagation and dynamic manipulation by using the spin-orbit torque induced ferromagnetic resonance and time-resolved magneto-optic Kerr effect (MOKE) technique as well as other method. The implement of this project will make the magnonic crystal more reconfigurable and realize its ultrfast manipulation. The results obtained in this project provide scientific basis for designing the ultrafast programmable magnonic devices.

磁体形状和物质参数周期性调制磁子晶体的研究近年来取得了很大进展，但这类磁子晶体很难实现其重构和动态调控，尤其是超快调控。磁子晶体的可重构性和动态调控是研制可编程的高速磁子器件所必需的。本项目提出磁结构周期性分布的磁构型磁子晶体，由于磁结构可通过外场或自旋转移（自旋-轨道）力矩来改变，且磁结构的驰豫时间在纳秒尺度，因此这类磁子晶体更易于重构，可实现超快调控。我们将采用微磁学理论研究诸如畴壁、斯格明子等磁构型磁子晶体的形成条件、自旋波的传播特性及其动态调控；采用分子束外延、磁控溅射和微纳加工工艺制备出纳米带畴壁磁子晶体，通过自旋-轨道力矩激发的铁磁共振和时间分辨的磁光克尔效应等方法测量畴壁磁子晶体的磁动力学性质、自旋波的传播及其调控。通过本项目的实施实现磁子晶体的可重构和动态调控尤其是超快调控，为研制可编程的超快磁子器件提供科学依据。

磁子自旋学的核心问题是自旋波的调控，磁子晶体是调控自旋波的有效方法，目前所研究的磁子晶体大多数是结构固体的，很难实现自旋波的动态调控。本项目提出了磁构型磁子晶体，既拓扑磁结构周期性变化的磁子晶体，研究了磁构型磁子晶体的形成、动力学性质和动态调控，自旋波在磁构型磁子晶体中的传播特性和多场调控，自旋波信号和电信号之间的相互转换。重要结果有：（1）制备了磁性过渡金属单层和多层膜、具有垂直磁各向异性的GdFeCo和TbFeCo非晶膜，以及相应的纳米带测量器件。测量到纳米带中畴壁的多个本征振荡模式和纳米带磁子晶体中的多个自旋波模式。（2）在纳米带中通过外场或自旋极化电流可实现布洛赫和奈尔畴壁磁子晶体的注入。施加外场或自旋极化电流可动态的调控磁子晶体的周期和周期势强弱，快速的产生或湮灭磁子晶体。在具有Dzyaloshinskii-Moriya相互作用的磁性膜中，或软磁纳米点阵列和磁性膜耦合体系中形成了斯格明子磁子晶体，通过脉冲场可实现纳秒尺度下斯格明子阵列的打开和关闭。（3）自旋波在磁构型磁子晶体中传播形成能带结构，带隙位置和宽度由磁子晶体的结构决定，通过外场或自旋极化电流控制磁子晶体的结构，实现对自旋波位相、能带带隙位置和宽度的超快调控，打开或关闭能带。（4）提出了在具有较强磁-电耦合的磁体中自旋波的电场调控和电场激发。（5）提出了铁磁体中自旋转移力矩诱导的左旋极化自旋波的概念。（6）发现铁磁/重金属/铁磁多层膜在自旋轨道力矩作用下是具有PT对称性的非厄密哈密顿体系，通过例外点（EP 点）实现了对自旋波的高效调控。（7）提出了一个自洽统一的理论，给出了重金属/铁磁界面磁子自旋与电子自旋相互转换的物理机理，发现了这种转换的非线性和单向性效应。上述研究对自旋波的动态调控、设计研制可编程的磁子自旋器件提供了科学依据和方案。发表SCI学术论文32篇，培养了4名博士研究生和5名硕士研究生。