Tuning isolated zero-field skyrmions and spin spirals at room-temperature in synthetic ferrimagnetic multilayers

Abstract

We demonstrate the observation of spin spirals and individual skyrmions in synthetic Pt/CoGd/Pt ferrimagnetic multilayers at room-temperature without the assistance of an external magnetic field. The magnetic coupling between the magnetic moments of Co and Gd, was investigated across various CoGd thicknesses by element specific X-ray magnetic circular dichroism (XMCD) performed around the Co L2,3 and Gd M4,5 edges. It shows an uncompensated ferrimagnetic orientation between the Co and Gd atoms preserved at ambient conditions, even for sub-nanometer thick layers. In addition, with the tunable enhanced perpendicular magnetic anisotropy Ku and remnant magnetization MR found for thinner CoGd ≤ (0.9 nm) isolated zero-field skyrmions were imaged by magnetic force microscopy (MFM) as the magnetic ground state, replacing the spin spirals observed for thicker CoGd layers ≥ (1.2 nm). Such stable skyrmions in perpendicularly magnetized materials with antiparallel exchange-coupling are potential candidates for energy-efficient data storage and processing in future antiferromagnetic-based devices.