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MMM 2022

November 07, 2022

Minneapolis, United States

Tuning domain wall chirality of Pt/Co/Pt based Perpendicularly Magnetized systems with Au insertion

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, Deff 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 Hz in presence of Hx. 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 (HDMI) in PMA system. The Hx dependence of the DMV has a minimum at Hx = HDMI. iDMI strength calculated using the formula described by Je et. al 6 and displayed in Fig. 2. The Deff 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. Deff 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 Deff 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.
1. S. S. Parkin, M. Hayashi, and L. Thomas, Science 320, 190–194 (2008)
2. A. Fert, V. Cros, and J. Sampaio, Nature nanotechnology 8, 152–156 (2013)
3. C. Onur Avci, K. Garello, and P. Gambardella, Applied Physics Letters 100, 212404 (2012)
4. V. M. P, K. R. Ganesh, and P. S. A. Kumar, Phys. Rev. B 96, 104412 (2017)
5. S. Guddeti, A. K. Gopi, and P. S. Anil Kumar, IEEE Transactions on Magnetics 54, 1–5 (2018)
6. S. G. Je, K. J. Lee, and S. B. Choe, Physical Review B 88, 214401 (2013)
7. H. Yang, A. Fert, and M. Chshiev, Phys. Rev. Lett. 115, 267210 (2015)

Asymmetric expansion of bubble domain at an in-plane magnetic field,Hx = 30 mT of (a) Au (t = 0 nm) and (b) Au (t = 0.3 nm)

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

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