Tunable magnetic skyrmions in ferrimagnetic Mn4N

Thin films of ferrimagnetic Mn4N are candidate materials to host magnetic skyrmions that have demonstrated thermal stability up to 450 degrees C. However, there are no experimental reports observing skyrmions in this system. Here, we discuss the results of sputter grown 15-17 nm Mn4N thin films on the MgO substrate capped with Pt1-xCux layers. Vibrating sample magnetometry measurement of out-of-plane hysteresis loops confirmed that magnetic properties are insensitive to the cap layer composition. Imaging based on magnetic force microscopy measurements observed 300-50 nm sized skyrmions, as the Cu concentration was increased from x = 0-0.9. We performed density functional theory calculations and found that the interfacial Dzyaloshinskii-Moriya interactions (iDMI) follow a trend: Mn4N/MgO(001) < Cu/Mn4N(001) < Pt/Mn4N(001). We infer from these calculations that x in the Pt1-xCux capping layer can serve as a robust tuning knob to tailor the iDMI and control the skyrmion size. This work provides guidance to achieve smaller Neel-type skyrmions in Mn4N thin films, which is an important step forward for building thermally stable skyrmionic devices.