Thermal Spin Accumulation and Spin-Transfer Torque Driven by Chirality Induced Spin Selectivity Effect in Layered Chiral Hybrid Perovskite

Transistor based nano-electronic devices have shown rapid development over the past few decades. Their performance, however, is limited mostly by the excessive heat generation due to continuous current charge-discharge cycles. Naturally, a higher transistor density correlates to enhanced nano-electronic device performance. Therefore, there have been attempts to incorporate more transistors into limited space to enhance computation processing and data transferring speed. But this approach has reached its peak in the development of the nano-electronic device because (1) the limitation of the cooling capacity on the circuit and (2) the limitation of decreasing the size of the transistor due to quantum tunneling. Researchers have been proposing new paradigms to overcome the limitations of the existing nano-electronics. One such novelty lies in utilizing the spin of electrons that is also known as the intrinsic angular momentum of electrons. The spin of electrons can be up (1) and down (0) depending on the direction of the angular momentum that acts as a switch. This spin switch can replace the existing transistor-based electronics with similar performance but significantly lower heat generation. Thermal spin-transfer torque (STT), the transfer of the spin current mediated by heat current, provides a new way to control the orientation of nanomagnets. The recent discovery of the Chiral-Induced Spin Selectivity (CISS) effect offers an opportunity to create a spin current in chiral materials without the need of ferromagnetic elements, e.g., chiral (left- or right-handed) molecules. In the presence of electron transport mediated by heat current, the chiral materials would produce a spin current via the CISS effect, of which the spin polarization determined by the handedness of the material. Here we study the CISS effect in solution-processed, 2D-layered, hybrid perovskite materials incorporating chiral molecule ligands, sensed by the thermal accumulation and STT signal using ultrafast Time-Resolved Magneto-Optical Kerr Effect (TR-MOKE) technique. In the TR-MOKE method, the spin accumulation on a non-magnetic film surface (e.g., Cu) or the spin transfer torque on a ferromagnetic film surface (e.g., CoFeB) can be measured. When the pulsed laser beam creates the temperature gradient in the chiral layers on the silicon substrate, the chiral molecule layer is thermally activated. The temperature difference across the chiral molecule films creates a chirality-determined spin current by the thermally induced CISS effect and injects it into the non-magnetic layer or ferromagnetic layer, which leads to a thermally induced spin accumulation or spin-transfer torque (STT). We successfully observed the chirality-dependent spin accumulation in the non-magnetic layer and precession of the magnetization in the ferromagnet layer on top of layered chiral hybrid perovskites, which is attributed to the CISS effect. Our work opens a new route for the use of layered chiral hybrid perovskite materials for novel STT devices.