Energy efficient spin-torque devices

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In most electronic devices, only the charge of electrons is utilized while another feature spin has unexplored advantages. The spin of electrons is a quantum-mechanical property that offer advantages to achieve future generations of electronics that can operate faster while consuming less energy. To date, most activities in spintronics have largely been focused on ferromagnetic materials where all the spins are aligned in the same direction and is relatively easy to read, write and store information with high fidelity. Currently, it is believed that the manipulation of spin can be even faster and potentially more energy efficient in another class of material called ferrimagnets, where the spins of different atoms point in opposite directions. In this project, the PIs proposes to investigate ferrimagnets-based devices and explore new methods to read and write information. Novel device structures, and theoretical models will be developed. The results of this research will potentially impact a wide range of applications in memory, logic, data storage, neuromorphic computing, and radiofrequency devices. In addition, the project will provide valuable training opportunities for graduate and undergraduate students, specifically from underrepresented and minority groups. In addition, the PIs will actively participate in direct outreach to the public in local or national events.In recent years, ferrimagnets have gained a great deal of attention due to their unique properties. The staggered moments in fully compensated ferrimagnets result in a zero net magnetization, which allows spin currents to penetrate much deeper, a potentially very useful feature in increasing the efficiency of spin-torque switching. Intriguing physics also exists at the angular momentum compensation points of ferrimagnets, where a finite magnetization and nonzero spin polarization persist, enabling the exploration of antiferromagnetic-like fast dynamics in ferrimagnets. In this project, the PIs will carry out a joint experimental-theoretical investigation on devices based on ferrimagnets, specifically, on spin-transfer torque and spin-orbit torque effects where the magnetization can be switched by an electric current. The PIs will develop novel devices where the ferrimagnets will be actively participating in the magnetoresistance and spin angular moment transfer process, instead of only passively providing perpendicular magnetic anisotropy to the system. Both two-terminal and three-terminal devices will be investigated, to understand the spin-transfer torque and spin-orbit torque effects, respectively. The research will be focused on the interaction of spin-polarized tunneling current with the two sublattices of ferrimagnets, to understand the roles of different spin torques (damping-like vs field-like) and to realize possible anti ferromagnetic-like dynamics in switching experiments down to 100ps.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.