Rare Earth Garnets for Spintronic Research

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Abstract

Non-technical abstract New devices that can carry out memory or logic operations with low power consumption are under intense development. "Spintronic" phenomena, in which the magnetic state of a material can be controlled and detected by using an electrical signal, provide a path towards a family of such devices. This program develops novel materials and investigates their growth, structure and properties, and how their properties can be controlled. The materials are based on garnet, which is a naturally occuring oxide. The properties and behavior of the garnet can be manipulated over a wide range, leading to new opportunities in spintronic research and applications. The broader impacts of this work include the training of graduate and undergraduate students, including those who have been traditionally underrepresented in science and engineering, and the development of materials and knowledge that will contribute to room temperature spintronic devices. Public outreach is carried out via the NanoObservatory event at the Cambridge Science Festival, where the public is introduced to nanofabrication and nanotechnology at MIT, and by incorporation of modules on spintronics in free online courses. Technical abstract This proposal addresses key issues in materials and spin physics which will point the way towards room temperature spintronic devices. Spintronic phenomena are under intense investigation due to their promise in enabling memory or logic devices with low power consumption. Ferromagnetic insulators are particularly interesting because they convey spin currents without charge currents, and exhibit low damping and high temperature functionality. One of the most prominent classes of such systems is that of iron garnets, of which the best studied is yttrium iron garnet, but substitution of rare earth ions on the Y sites enables exceptional control over the magnetic properties. The intellectual merit of this work is to develop synthesis methods and examine spin orbit torque - driven domain wall motion in iron garnet films with perpendicular magnetic anisotropy. Materials properties are designed by substituting rare earths such as thulium into the garnet structure to alter the magnetocrystalline anisotropy, magnetoelastic coefficients and lattice strain, damping and compensation temperature, and by diluting the Fe sublattices to change the net magnetization. The behavior of domain walls in garnet is probed at various temperatures during current or field pulsing, taking advantage of the high Faraday rotation and magnetooptical Kerr effect measurements even for very thin (few-nm) films where magnetometry is unsuitable, and complemented by measurements of spin Hall magnetoresistance. The broader impacts of this work include the training of graduate and undergraduate students and the development of a set of materials and an increased understanding of heterostructures that will contribute to room temperature spintronic devices. Public outreach is carried out via the NanoObservatory event at the Cambridge Science Festival, where the public is introduced to nanofabrication and nanotechnology at MIT, and by incorporation of modules on spintronics in free online courses. Given the ever-increasing diversity in the national workforce, the PI will be proactive in recruiting students who have been traditionally underrepresented in science and engineering. 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.