No abstract

No abstract

Current-induced magnetic domain wall motion at zero magnetic field is observed in the permalloy layer of a spin-valve-based nanostripe using photoemission electron microscopy. The domain wall movement is hampered by pinning sites, but in between them high domain wall velocities (exceeding 150 m/s) are obtained for current densities well below 10 12 A/m 2 , suggesting that these trilayer systems are promising for applications in domain wall devices in case of well controlled pinning positions. Vertical spin currents in these structures provide a potential explanation for the increase in domain wall velocity at low current densities.Moving magnetic domain walls using electric currents via spin-torque effects rather than using a magnetic field is one of the recent exciting developments in spintronics 1 . Since the prediction of spin-torque effects 2 , many experimental 3,4,5,6,7,8,9,10,11,12,13,14,15 and theoretical 16,17,18 works have been dedicated to the study of currentinduced domain wall motion (CIDM). Besides fundamental investigations, the use of domain walls in logic 19 and memory 20 devices has already been proposed. Low current densities and high domain wall (DW) velocities at zero magnetic field are required for future applications.Direct evidence of CIDM at zero field has been reported for several nanostripe systems, including permalloy (FeNi) 6,11 , magnetic semiconductors 9 and systems with perpendicular magnetization 7,12,14,15 . For the commonly used FeNi system, the critical current densities are not much below 10 12 A/m 2 at zero magnetic field 8,11 , associated with DW velocities going from some m/s up to about 100 m/s 11 . Much lower critical currents are found for magnetic semiconductors like GaMnAs (about 1 × 10 9 A/m 2 ) because of the low magnetic moments, but the observed DW velocities are small (< 1 m/s) 9 . Moreover, these materials are not ferromagnetic at room temperature. Low current density values are also found in spin-valve-based nanostripes with either in-plane 3,10 or perpendicular anisotropy 7 . Additionally, transport measurements in FeNi/Cu/Co trilayers show CIDM induced by subnanosecond current pulses 5 , indirectly indicating high DW velocities in such spin-valve-based systems. In this work, we show that in these systems CIDM at zero magnetic field can take place with high DW velocities (exceeding 150 m/s) at current densities well below 10 12 A/m 2 . These high velocities are observed only in certain regions of the nanostripes, where domain wall pinning is limited. Currents perpendicular to the plane in the vicinity of the DW are probably partly responsible for this increase in efficiency, which makes the trilayer systems possible candidates for spintronic applications based on CIDM if pinning can be controlled.We observed domain wall motion in the FeNi layer of 400 nm wide FeNi (5 nm)/Cu (8 nm)/Co (7 nm)/ CoO (3 nm) nanostripes, by using Photoemission Electron Microscopy (PEEM) combined with X-ray Magnetic Circular Dichroism (XMCD) 21 . The Cu spacer layer is chosen to ...