Enhancement of perpendicular magnetic anisotropy and Dzyaloshinskii–Moriya interaction in thin ferromagnetic films by atomic-scale modulation of interfaces

To stabilize nontrivial spin textures, e.g., skyrmions or chiral domain walls in ultrathin magnetic films, an additional degree of freedom, such as the interfacial Dzyaloshinskii–Moriya interaction (IDMI), must be induced by the strong spin-orbit coupling (SOC) of a stacked heavy metal layer. However, advanced approaches to simultaneously control the IDMI and perpendicular magnetic anisotropy (PMA) are needed for future spin-orbitronic device implementations. Here, we show the effect of atomic-scale surface modulation on the magnetic properties and IDMI in ultrathin films composed of 5d heavy metal/ferromagnet/4d(5d) heavy metal or oxide interfaces, such as Pt/CoFeSiB/Ru, Pt/CoFeSiB/Ta, and Pt/CoFeSiB/MgO. The maximum IDMI value corresponds to the correlated roughness of the bottom and top interfaces of the ferromagnetic layer. The proposed approach for significant enhancement of PMA and the IDMI through interface roughness engineering at the atomic scale offers a powerful tool for the development of spin-orbitronic devices with precise and reliable controllability of their functionality. Introducing surface roughness at the atomic scale can improve control of magnetic patterns in thin films, which is potentially useful for very low-power consumption memories. Swirling magnetic-field patterns can form in ultra-thin layers of magnetic materials. Alexander Samardak from the Far Eastern Federal University, Vladivostok, Russia, Young Keun Kim from Korea University, Seoul, Republic of Korea, and their co-workers have identified a method for improving the strength of the so-called interfacial Dzyaloshinskii–Moriya interaction (IDMI), which can influence the dynamics of these magnetic patterns. The team sandwiched a thin film of the ferromagnet cobalt-iron-silicon-boron between two metallic layers and demonstrated the IDMI was correlated with the roughness of the bottom and top interfaces. Using surface roughness, they were able to achieve a 2.5-fold increase in the IDMI. An effect of atomic-scale surface modulation on the magnetic properties and the interfacial Dzyaloshinskii-Moriya interaction (IDMI) is shown in Pt/CoFeSiB/X(MgO, Ta, Ru) ultrathin films sputtered on the epitaxial Pd layers of the different thickness and surface morphology. The correlated roughness of the bottom and top interfaces of CoFeSiB increases IDMI values by up to 2.5 times, with the maximum magnitude Deff = −0.88 erg/cm2. The main reasons for this significant enhancement are the intermixing at interfaces and the correlated interface-roughness variations, which both affect electronic transport across the interface and, as a result, the degree of the electron scattering.