Thrust 1 : Pure Spin and Magnonic Current Control
The main focus is on the exploration of more efficient generation and detection of pure spin currents in metals and insulators and more efficient spin current-driven magnetization dynamics in both magnetic metal and insulator devices.
Pure spin current can be generated in several ways, e.g. by spin pumping (Fig. 1(a)), heat (Fig. 1(b)), or spin Hall effect. In a non-magnetic material, the pure spin current, Js, decays over a characteristic length called spin diffusion length ranging from ~1 nm to microns. Js can be converted to an electric field or voltage by a heavy metal such as Pt or Au with strong spin-orbit coupling. One important but poorly experimentally determined parameter that affects the efficiency of both generation and detection of Js is the spin Hall angle. Chien and M.Z. Wu will work on various material structures and experimental techniques such as ferromagnetic resonance and longitudinal spin Seebeck effect to more precisely determine the spin Hall angle by excluding other extrinsic factors. With the theoretical support from R.Q. Wu, the team aims to develop a better understanding of spin current transport phenomena in thin films and heterostructures.
The left panel shows the test device structure for measuring propagating spin waves in time-domain and the right panel shows time-resolved data from a propagating spin wave packet in 100 nm thick Co30Fe70 film.
In magnetic insulators, the pure spin current is carried by spin waves whose excitations are called magnons. Similar to phonons, excitations of lattice waves, magnons carry energy and linear momentum. In addition, magnons also carry angular momentum which can exert a torque on the magnetization of another magnetic material to cause it to precess or switch. Chen, Chien and Khitun study the propagation of magnons generated by heat or ferromagnetic resonance in magnetic metals or insulators and the spin transfer torque exerted by the magnon currents.
Theme 1 members will collaborate with other members in SHINES on heterostructure growth (Shi and Wang) and device fabrication (Krivorotov), spin wave imaging (Li) and micromagnetic simulations (Lake).
Theme members: Chien, Chen, Khitun, M.Z. Wu and R.Q. Wu
Cross-theme members: Lake (T2), Li (T2), Shi (T2), Wang (T3), and Krivorotov (T3)