ECCS-EPSRC: Collaborative Research: Acoustically induced Ferromagnetic Resonance (FMR) assisted Energy Efficient Spin Torque memory devices

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Magnetic Random-Access Memory (MRAM) based on nanoscale magnets can retain information when power is turned off; such non-volatile memory cannot be implemented with Complementary Metal Oxide Silicon (CMOS) technology alone. However, the energy and current required to switch a state-of-the-art MRAM device is large, which limits their use to niche applications. Strain and acoustic waves can be used to significantly lower the current required to write information in such devices, but unfortunately which lacks energy density making them ineffective for nanoscale magnets scaled to very small lateral dimensions (well below 100 nanometers). The key innovation proposed in this project is to use surface acoustic waves (SAW) induced ferromagnetic resonance (FMR), a phenomenon by which energy applied to the nanomagnets is accumulated over tens of cycles to produce a large magnetization deflection in a few nanoseconds to significantly lower the current needed to switch the magnetic state of extremely small nanomagnets. This research could lead to dense, energy efficient, and non-volatile magnetic memory. The Virginia Commonwealth University (VCU) and Massachusetts institute of Technology (MIT) PIs will work with industry to transfer relevant research developments, incorporate magnetic memory modules in graduate or undergraduate classes, hold nanomagnetism workshops for high school students and engage in outreach to under-represented K-12 students through workshops and/or hosting them as summer research interns. The project work will consist of complementary materials growth and characterization (MIT), nanofabrication (MIT and VCU), device characterization (VCU), advanced time-resolved magnetization visualization (Univ. of Exeter, UK), modeling and simulation (VCU). The tasks include: (i) Growth and patterning of nanoscale magnets and deposition of interdigitated transducers (IDT) to generate SAW on piezoelectric Lithium Niobate films. (ii) Characterization of magnetization reversal in the above nanostructures with magnetic force microscopy (MFM) to find optimum SAW and spin current conditions. Samples thus identified will be sent to Exeter Univ. for study of detailed time resolved magnetization dynamics with time resolved scanning Kerr microscopy (TRSKM) under (a) SAW induced FMR (b) spin torque and (c) combination of both “a” and “b”. (iii) Performing micromagnetic modeling of the magnetization dynamics to explain the TRSKM studies and understand the dynamic error in the presence of realistic thermal noise, defects, edge roughness, etc. under combination of SAW induced FMR and SOT/STT. This closely coordinated research project would advance knowledge of rich non-linear magnetization dynamics under SAW induced FMR, spin torque and a combination of both as well as provide a proof-of-concept demonstration of this energy efficient and scalable non-volatile memory concept.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.