Interfacial Dzyaloshinskii-Moriya interaction in perpendicularly-magnetized Pt/Co/AlO$_x$ ultrathin films measured by Brillouin light spectroscopy

摘要

Spin waves in perpendicularly-magnetized Pt/Co/AlO$_x$/Pt ultrathin filmswith varying Co thicknesses (0.6-1.2 nm) have been studied with Brillouin lightspectroscopy in the Damon-Eshbach geometry. The measurements reveal apronounced nonreciprocal propagation, which increases with decreasing Cothicknesses. This nonreciprocity is attributed to an interfacialDzyaloshinskii-Moriya interaction (DMI), which is significantly stronger thanasymmetries resulting from surface anisotropies for such modes. Results areconsistent with an interfacial DMI constant $D_s = -1.7 \pm 0.11$ pJ/m, whichfavors left-handed chiral spin structures. This suggests that such films below1 nm in thickness should support novel chiral states like skyrmions.