Observation of large perpendicular magnetic anisotropy and excessive polar magneto-optical effect in Pt/CoFeB/Ru tri-layer system

Abstract

Heterostructures comprising ferromagnet (FM) and heavy metals (HM) with perpendicular magnetic anisotropy (PMA) and interfacial Dzyaloshinskii-Moriya interaction (iDMI) can host chiral domain walls and topological spin textures, making them highly promising for various spintronics applications. In this paper, we have investigated the magneto-optical properties, the anomalous Hall effect (AHE), and PMA of Pt/CoFeB/Ru multilayers engineered to possess significant iDMI. We utilized the Anomalous Hall effect (AHE), and the polar magneto-optical Kerr effect (p-MOKE), Hall response and the domain wall motion in Pt/CoFeB/Ru-systems. Both MOKE and AHE measurements confirm that the films maintain strong perpendicular magnetization for CoFeB thicknesses below 1.2 nm. The effective magnetic anisotropy K_{\mathrm{eff}} of 0.88 \times 10^6 erg/cm^3 has been achieved without any post-annealing, highlighting the high-quality interface in this multilayer design. The angular dependence of the switching field deviates from the conventional Kondorsky model and is well described using a modified Kondorsky formalism, capturing the role of field-induced domain-wall softening and pinning effects in the reversal process. Furthermore, p-MOKE microscopy imaging during the magnetization reversal process provides detailed insight into domain nucleation and subsequent domain-wall propagation. The observations reveal well-defined, stable magnetic domains that evolve coherently under the applied magnetic field. Such a behavior is expected in the system where interfacial DMI, PMA interact to stabilize the chiral N\'eel-type domain walls, which are essential for fast, low-power domain-wall motion driven by spin-orbit torques.