Tunable Magnetic Skyrmions in Ferrimagnetic Mn₄N

The magnetic skyrmion has large potential in high-density data storage applications due to its unique properties. To get a high data density, the skyrmions should be small at room temperature (RT). Simulations and experiments have found 10–30nm small skyrmions in GdCo thin films at RT, but CoGd thin films would lose their perpendicular magnetic anisotropy at high temperatures (300 ^oC). Ferrimagnetic Mn­­₄N thin film is one of the candidate materials to host small magnetic skyrmions with much improved thermal stability. Here, we discuss the results of sputter-grown ~15 nm Mn4N thin films on MgO substrate with Cu_xPt_1-x capping layers. The optimal films showed low saturation magnetization and low magnetic anisotropy energy, which were insensitive to the composition of the capping layer. Magnetic force microscopy images showed the diameter of the magnetic skyrmion decreased from 300nm to 50nm, as the Cu concentration was increased from x= 0 to 0.9. The interfacial Dzyaloshinskii-Moriya Interaction (iDMI), as calculated by DFT, decreases with Cu substitution and is likely the source of the decrease in skyrmion radius. The DFT results will be discussed in greater detail in a separate talk.  This work provides guidance to achieve smaller Néel-type skyrmions in Mn4N thin films.