Perpendicular magnetic anisotropy (PMA) systems that involve HM/FM/HM tri-layer structure have immense scope for constructing high speed memory devices 1,2. Broken inversion symmetry at HM/FM interface introduces interfacial Dzyaloshinskii- Moriya interaction (iDMI) which stabilizes chiral Neel wall that can be manipulated with spin polarized current. The current induced deterministic switching of PMA systems also realized with 3 or without 4,5 application of bias magnetic field. Several methods have been introduced to estimate the iDMI of HM/FM/HM as well as HM/FM/metal-oxide thin films in last few years. In this work, we have used field induced domain wall motion (FIDWM) to estimate iDMI strength, D_eff of sputter deposited Ta (3.5 nm)/Pt (3 nm)/Co (0.4 nm)/Au (x nm)/Pt (1 nm) thin films where x = 0, 0.3, 0.5 and 0.7 nm. The domain wall velocity (DMV) of a nucleated bubble domain was estimated applying pulsed H_z in presence of H_x. The asymmetric expansion of bubble domain reveals the chirality of domain wall of the samples. Ta/Pt/Co/Pt systems has Neel walls with right-handed chirality whereas the chirality reverses with introduction of ultrathin Au layer as shown in Fig. 1. The iDMI can be manifested as an effective in-plane magnetic field (H_DMI) in PMA system. The H_x dependence of the DMV has a minimum at H_x = H_DMI. iDMI strength calculated using the formula described by Je et. al 6 and displayed in Fig. 2. The D_eff of symmetric Ta/Pt/Co/Pt system have very small negative value which can be attributed to the difference of roughness of bottom Pt/Co and top Co/Pt interface. D_eff increases as the asymmetry around Co layer was introduced with insertion of Au layer. The maximum Deff was observed for the sample with highest degree of asymmetry (Au thickness = 0.7 nm). The D_eff also becomes positive when Au is introduced at top Co/Pt interface. The Pt/Co and Au/Co interface has opposite polarity of iDMI 7. These two interfaces of Ta/Pt/Co/Au/Pt effectively reverse the iDMI sign.
References
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Asymmetric expansion of bubble domain at an in-plane magnetic field,H_x = 30 mT of (a) Au (t = 0 nm) and (b) Au (t = 0.3 nm)

Effective in-plane field of iDMI, H_DMI and iDMI strength, D_eff as a function of Au layer thickness