Effect of spin transfer torque on domain wall motion regimes in [Co/Ni] superlattice wires

Statistical study of domain-wall depinning induced by magnetic field and current in an epitaxial Co/Ni-based spin-valve wire

“…By fitting the DW depinning at 50% on entire of the map, with revisited Arrhenius law by taking into account the impact of STT, Oersted field and Joule heating on the energy barrier, we have (i) estimated the position of the pinning site from the border of the wire and (ii) extracted specific parameters attributed to STT effect both adiabatic and nonadiabatic term [25][26][27]. The values of both terms are close to those obtained previously for a single [Co/Ni] layer [18] which validates the experimental method.…”

“…(ii) No new DW nucleation ever occurred on the left part of the wire by Kerr microscopy during the experiment. (iii) We have checked that the maximum current density 40×10 10 A/m² is too low in our system to observe the counterintuitive STT-driven DW depinning against a high H app as already seen for Co/Ni [18,34] and for having a DW depinning at µ 0 H app =0 mT. Note that we previously estimated the current density threshold where this counterintuitive STT-driven occurs for DW motion to be about 30×10 10 A/m² in epitaxial Co/Ni wires [18].…”

“…The free layer is the [Co(0.5)/Ni(0.6))] ×3 and the hard layer is [Ni(0.6)/Co(0.2))] ×5 . The free layer is similar than Co/Ni single layer already studied previously [18,29]. The crystallinity and the interfaces quality have been checked during deposition by recording RHEED pattern and oscillation, as well as by transmission electron microscopy [30].…”

“…Materials with perpendicular magnetic anisotropy (PMA) are promising candidates [8][9][10], as they can host small domain size with narrow DWs [11], useful for maximizing storage density and improving current-induced domain wall displacement efficiency. Several studies have shown that [Co/Ni] superlattices are considered as an interesting material for nanostructured spintronics devices because of their tunable magnetic and spin-electronic features [8,[12][13], especially for domain wall motion by STT [14][15][16][17][18].…”

“…When a polarized-current is injected through a wire, several effects can arise. In our experimental set-up and sample, the used of (i) large and especially thick (spacer and double layer of Co/Ni) stack increase the Oersted field creates by the in-plane current (as regard of Co/Ni single layer where expected Oersted field is low [18]) , (ii) ms range pulses duration give the Joule heating significant, (iii) gold for the capping and seed layer and the symmetry of the stack prevent spin-orbits torque observed in ferromagnetic nanowire with structural inversion asymmetry [23,37]. As consequence in our system, 3 major effects as STT, Joule heating and Oersted field are expected to be not negligible and can help to depin the DW.…”