Emergence of Sizeable Interfacial Dzyaloshinskii-Moriya Interaction at Cobalt/Fullerene Interface

Abstract

The interfacial Dzyaloshinskii-Moriya interaction (iDMI) originating from a heavy-metal/ferromagnet (FM) interface plays a crucial role in stabilizing chiral spin textures in magnetic multilayers. Recently, graphene based on the low-spin-orbit-coupling (SOC) element carbon ($\mathrm{C}$) has shown a significant iDMI owing to the Rashba SOC when deposited on top of $\mathrm{Co}$. A similar enhanced SOC has been reported earlier for other $\mathrm{C}$ allotropes, namely fullerene (${\text{C}}_{60}$) and carbon nanotubes, and a sizeable DMI can be expected to emerge from them. In this context, we elucidate the magnetization-reversal mechanism, the domain-wall (DW) dynamics, and the strength of the iDMI in a $\mathrm{Pd}(4.0\phantom{\rule{0.2em}{0ex}}\mathrm{nm})/\mathrm{Co}(0.5\phantom{\rule{0.2em}{0ex}}\mathrm{nm})/{\text{C}}_{60}({t}_{{\mathrm{C}}_{60}})/\text{Pd}(2.0\phantom{\rule{0.2em}{0ex}}\mathrm{nm})$ system with varying ${t}_{{\mathrm{C}}_{60}}$. The field-induced DW velocity measured in the creep region shows a DW velocity 2 orders of magnitude higher for a sample with 1.6 nm of ${\text{C}}_{60}$, due to a lower depinning field and spin-dependent hybridization at the $\text{Co}/{\text{C}}_{60}$ interface. Further, DMI measurements performed by use of the asymmetric DW expansion method exhibit a systematic increase in the iDMI from $\ensuremath{-}0.07$ to $\ensuremath{-}0.46\phantom{\rule{0.2em}{0ex}}\mathrm{mJ}/{\mathrm{m}}^{2}$ with an increase in ${t}_{{\mathrm{C}}_{60}}$. Such an enhanced iDMI turns an achiral Bloch wall into a chiral N\'eel wall. The emergence of a finite DMI (${D}_{\mathrm{Co}/{\mathrm{C}}_{60}}\ensuremath{\sim}\ensuremath{-}0.11\phantom{\rule{0.2em}{0ex}}\mathrm{mJ}/{\mathrm{m}}^{2}$) from the $\text{Co}/{\text{C}}_{60}$ interface is particularly encouraging for the use of $\mathrm{C}$-based materials in chiral-DW-based device applications.