Nanoscale spin dynamics in ferromagnetic/normal-metal heterostructures for spin-logic application : Engineering of spin-torque efficiency in Co2FeAl/β-Ta and Ru/FeCo/Ru multi-layers

Sammanfattning: In the present information age, people across the globe generate an enormous digital footprint. Therefore, it is necessary to store and process the information in an elegant way. Spin-logic circuits are being considered potential candidates beyond CMOS integrated computing due to high clock speed, non-volatility, and higher logical efficiency. A basic building block for spin-logic circuits is ferromagnetic (FM) and normal-metal (NM) heterostructures. An example of a spin-logic data processing circuit is the spin-orbit torque (SOT) magnetic random access memory (MRAM). Energy efficient operation of such circuits depends on the interfacial electronic and magnetic properties of the heterostructures. These properties are known as Gilbert damping of the FM layer, spin Hall angle of the NM layer, spin-mixing conductance and spin-memory loss at the interface. To reduce the power consumption of such circuits, we propose two methods; doping and interface engineering. In paper I, we use ultra-low damping Fe65Co35 thin films as the FM layer and Ru as the NM layer. The interfacial parameter, the spin-mixing conductance, of the FeCo/Ru heterostructure is enhanced by 98% with Re doping in the FeCo. In paper II, we use Co2FeAl as the FM layer and β-Ta as the NM layer, and inserting a Cu continuous layer at the interface of Co2FeAl/β-Ta, yielding an enhancement of the spin-mixing conductance. In both cases, the enhancement in spin-mixing conductance can be linked to the increase in number of quantum conductance channels on the NM side, which helps to reduce the power consumption, and may provide a direction towards ultra-fast efficient operation of spin-logic circuits.