Today we live in a digital world where digital data provides the underpinning of much of our life. Many processes both at home and in industry rely on digital data, the vast majority of which is stored in the cloud in magnetic disk drives, a technology that is more than a half a century old. This technology has evolved by ever-decreasing the size of the elementary magnetic data bits but it is generally regarded that this process has reached an end and a new technology is needed. The technology that has the potential to replace magnetic disk drives is Racetrack Memory. This technology invented by the PI of SORBET relies on recent advances in the field of spintronics. The basic concept is that digital data is encoded in magnetic domain walls, tiny nanoscopic objects that separate regions of magnetic material that have their magnetizations directed along opposite directions. These nano-objects are shifted along magnetic racetracks – tiny magnetic nano-wires – by current pulses. A series of domain walls are shifted synchronously backwards and forwards so that these data bits can be read or written at individual reading and writing devices built into or alongside the racetracks. Racetrack Memory has the potential to have enormous storage capacity beyond that of any solid state memory today and rivalling or exceeding that provided by magnetic disk drives. Moreover, since there are no moving parts, unlike disk drives, Racetrack Memory will be much more reliable and will consume vastly less energy.
A main objective of SORBET was to explore the fundamental physics of current induced motion of domain walls so as to find new materials and structures that could allow for more efficient and reliable domain wall motion. A second main objective was to explore means of creating nano-scopic racetracks that could be oriented perpendicular to the substrate on which they are formed. Finally, a third objective was to explore topological nanoscopic magnetic objects that could be used for storing digital data beyond domain walls. All of these objectives were met in SORBET. New efficient methods of manipulating domain walls via spin-orbit and giant exchange torques were discovered. A novel multi-photon lithographic technique was developed to allow for complex 3D racetracks to be fabricated. Anti-skrymions and elliptical Bloch skrymions, two novel and distinct topological non-collinear spin textures, were discovered in a family of inverse tetragonal Heusler compounds. The results of SORBET have pushed Racetrack Memory to the cusp of technological application.
