Skyrmion state of exchange coupled core-shell nanostructure

The intriguing magnetic states - skyrmion and skyrmion lattice - have been observed and created in helical magnetics, such as MnSi, Fe_1-xCo_xSi, the helical FeGe and monolayer Fe film [1-3]. The skyrmions in helical magnets are always associated with the chiral magnetic interaction, namely Dzyaloshinskii-Moriya interaction (DMI). However, several novel works present new approaches to create the skyrmion in nanostructures in absence of DMI [4-7]. Here, we study the skyrmion created in exchange coupled core-shell structure (Co/CoPt) without DMI. As shown in Fig. 1, exchange coupled core-shell disk and square has been modeled under the framework of micromagnetics. For the core-shell nanodisk, r represents the radius of core region, and R represents the radius of the whole nanodisk. Similarly, l represents the edge length of the core region and L represents the edge length of the whole nanosquare. t represents the thickness of the disk as well as nanosquare.