Executive Summary : | The spin transfer torque based magnetic random-access memory (STT- MRAM) is a non-volatile memory that has been successfully commercialized. For example, in 2019, both Everspin Technologies and Intel have started production for STT-MRAM chips. STT-MRAM offers advantages such as lower power consumption and better scalability compared to charge based memory technologies. However, the amount of current needed to switch the magnetization is presently too high, and the reduction of this current density is desirable. Recently discovered, spin-orbit toque (SOT) is one possible method to reduce the current density. The SOT is observed in bilayer systems consisting of a ferromagnet and a heavy metal with high spin-orbit coupling. A torque is experienced by the magnetization of a ferromagnet when a charge current flows in the heavy metal layer. Due to the symmetry requirements, the heavy metals (such as Pt, W, and Ta) generate spin current with spin polarization along the y-direction for a charge current flowing along the x-direction. This leads to a damping like torque, which is in-plane. However, for high density recording, one requires ferromagnetic layers with perpendicular magnetization. Such ferromagnetic layers with perpendicular magnetization can not be switched with the above in-plane torque generated by the heavy metals. An in-plane magnetic field is normally needed to switch the layer with perpendicular magnetization. In this proposal, we propose to use antiferromagnet (AFM) topological Kagome semimetals (TSM), a class of quantum material, to generate an out-of-plane torque and hence achieve switching at zero field. We plan to grow epitaxial thin films with different orientations of the Kagome lattice of these AFM-TSMs e.g., Mn₃Sn and Mn₃Ir, using magnetron sputtering. We expect that, in addition to efficient charge-to-spin conversion, an out-of-plane spin polarization will also be present depending on the orientation of the Kagome lattice. In addition, the spin momentum locking of surface states can result in high spin-charge conversion efficiency. These properties can be used for efficient field free switching of the perpendicularly magnetized systems, which will be grown on top of AFM-TSM. The proposed work will open a new and novel pathway to utilize the exotic topological properties and magnetism of the AFM TSM for efficient manipulation of magnetization for practical memory devices. |