Interfacial Dzyaloshinskii-Moriya interaction in perpendicularly magnetizedPt/Co/AlOxultrathin films measured by Brillouin light spectroscopy

Spin waves in perpendicularly magnetized ${\text{Pt/Co/AlO}}_{x}/\text{Pt}$ ultrathin films with varying Co thicknesses (0.6--1.2 nm) have been studied with Brillouin light spectroscopy in the Damon-Eshbach geometry. The measurements reveal a pronounced nonreciprocal propagation, which increases with decreasing Co thickness. This nonreciprocity, attributed to an interfacial Dzyaloshinskii-Moriya interaction (DMI), is significantly stronger than asymmetries resulting from surface anisotropies for such modes. Results are consistent with an interfacial DMI constant ${D}_{\mathrm{s}}=\ensuremath{-}1.7\ifmmode\pm\else\textpm\fi{}0.11\phantom{\rule{0.28em}{0ex}}\text{pJ}$/m, which favors left-handed chiral spin structures. This suggests that such films below 1 nm in thickness should support chiral states such as skyrmions at room temperature.