The sign of the interfacial Dzyaloshinskii–Moriya interaction in ultrathin amorphous and polycrystalline magnetic films

We investigate the sign of the interfacial Dzyaloshinskii–Moriya interaction (iDMI) energy density in system with inversion symmetry breaking for amorphous and polycrystalline ferromagnetic layers (CoFeB, Co) sandwiched by two different or the same heavy metals (Pt, Ta). By employing Brillouin light scattering, we observe non-reciprocal spin-wave dispersions which is a fingerprint of iDMI in SiO₂/(Pt,Ta)/(CoFeB, Co)/(Pt,Ta) systems. We carefully confirm that the signs of DMI of structurally inverted systems are changed accordingly. Negative iDMI for SiO₂/Pt/(CoFeB, Co)/Ta and positive iDMI for SiO₂/Ta/(CoFeB, Co)/Pt are observed, and iDMI of the symmetric structures (Pt/CoFeB/Pt and Ta/CoFeB/Ta) are not measureable with our Brillouin light scattering setup due to a negligible iDMI. For amorphous CoFeB, the magnitudes of iDMI are the same within the experimental error regardless the stacking order. For the textured Co, however, the magnitude of iDMI for Pt/Co/Ta is about 30 % larger than Ta/Co/Pt structure. (paper)