Temperature control of enhanced magnetic damping in ferrimagnetic Ni/Tb bilayers

Future magnonic devices which manipulate spin wave excitations as opposed to charge currents, offer a pathway towards novel, high performance and low-energy magnetic-logic devices. Here, magnetic damping is a crucially important parameter, controlling energy dissipation within the system. There is also emerging interest in the use of rare earth-transition metal (RE-TM) alloys and multilayer systems due to the ferrimagnetic nature of these systems, resulting in a plethora of useful phenomena, including ultrafast, energy efficient switching. While the mechanism for damping when interfacing magnetic thin films with conventional large spin orbit coupling materials such as Pt is well understood, it is far from clear within a RE-TM multilayer system, where large damping enhancements may arise from coupling between the elements.
In this proposal, we aim to examine the coupling of NiFe/Tb bilayers through Polarised Neutron Reflectivity (PNR) as a function of temperature. Temperature is a well established parameter for tuning the behaviour of RE elements within RE/TM systems, and the use of a depth sensitive probe such as PNR will allow us to determine the strength and thickness limits of any magnetic coupling within the system and the role it plays in enhancing the damping. Additionally, looking at this as a function of temperature will allow us to better understand the role of the magnetisation within the Tb layer, allowing us to further the capabilities of future devices.

以自旋波激发而非电荷电流为操控对象的未来磁子器件（magnonic devices），可为新型高性能低能耗磁逻辑器件的研发开辟全新路径。其中，磁阻尼（magnetic damping）是调控体系内能量耗散的核心参数。由于稀土-过渡金属（rare earth-transition metal, RE-TM）合金及多层膜体系具备亚铁磁性（ferrimagnetism），相关研究正受到愈发广泛的关注，这类体系可呈现出包括超快节能磁化翻转在内的诸多极具实用价值的物理现象。尽管将磁性薄膜与铂（Pt）等常规大自旋轨道耦合（spin orbit coupling）材料界面结合时的阻尼机制已得到充分阐明，但在RE-TM多层膜体系中，该机制仍远未明晰——此类体系中阻尼的大幅增强，可能源于组元间的耦合相互作用。
本研究计划旨在通过极化中子反射术（Polarised Neutron Reflectivity, PNR），探究NiFe/Tb双层膜的磁耦合特性随温度的变化规律。温度是调控RE/TM体系中稀土元素行为的成熟调控参数，而借助极化中子反射术这类深度敏感型探测手段，我们能够确定体系内任意磁耦合作用的强度与厚度极限，以及其在增强阻尼过程中所发挥的作用。此外，通过分析耦合特性随温度的演化规律，我们可进一步明晰铽（Tb）层内磁化强度的作用机制，从而为未来磁子器件的性能优化提供更坚实的理论支撑。