Synthetic ferrimagnet nanowires with very low critical current density for coupled domain wall motion

Serban Lepadatu, Henri Saarikoski, Robert Beacham, Maria Jose Benitez, Thomas A. Moore, Gavin Burnell, Satoshi Sugimoto, Daniel Yesudas, May C. Wheeler, Jorge Miguel, Sarnjeet S. Dhesi, Damien McGrouther, Stephen McVitie, Gen Tatara & Christopher H. Marrows


Domain walls in ferromagnetic nanowires are potential building-blocks of future technologies such as racetrack memories, in which data encoded in the domain walls are transported using spin-polarised currents. However, the development of energy-efficient devices has been hampered by the high current densities needed to initiate domain wall motion. We show here that a remarkable reduction in the critical current density can be achieved for in-plane magnetised coupled domain walls in CoFe/Ru/CoFe synthetic ferrimagnet tracks. The antiferromagnetic exchange coupling between the layers leads to simple Néel wall structures, imaged using photoemission electron and Lorentz transmission electron microscopy, with a width of only ~100 nm. The measured critical current density to set these walls in motion, detected using magnetotransport measurements, is 1.0 × 1011 Am−2, almost an order of magnitude lower than in a ferromagnetically coupled control sample. Theoretical modelling indicates that this is due to nonadiabatic driving of anisotropically coupled walls, a mechanism that can be used to design efficient domain-wall devices.

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