Room-Temperature Skyrmions at Zero Field in Exchange-Biased Ultrathin Films

Abstract

Magnetic skyrmions are topologically stable configuration with particle-like properties. Due to their efficient current-induced manipulation, they could act as carrier of information in futur devices. They where initially observed at low temperature and by applying an intense magnetic field in bulk materials exhibiting broken inversion symmetry[1-2] and in epitaxial ultrathin films with interfacial Dzyaloshinskii-Moriya interaction[3-4]. An intense research effort during the past few years has led to their stabilization at room temperature[5] but still by applying an external magnetic field. A promising strategy to overcome this last obstacle is to exploit the interlayer exchange coupling in magnetic heterostructure to produce an internal effective magnetic field Bint[6-7]. Here, we demonstrate that magnetic skyrmions with a mean diameter around 60 nm can be stabilized at room temperature and zero external magnetic field in an exchange-biased Pt/Co/Ni80Fe20/Ir20Mn80 multilayerstack[8]. This is achieved through an advanced optimization of the multilayer-stack composition in order to balance the different magnetic energies controlling the skyrmion size and stability. Magnetic imaging is performed both with magnetic force microscopy and scanning nitrogen-vacancy magnetometry, the latter providing unambiguous measurements at zero external magnetic field. Simulation of the PL quenching image are also achieved and the results, in agreement with experimental data, allows us to extract informations such as skyrmion's size. These results establish exchange-biased multilayer stacks as a promising platform toward the effective realization of memory and logic devices based on magnetic skyrmions.