Structural Imprinting of Target Skyrmions in Magnetic Multilayers

We will report on a recent study of topological spin textures that were imprinted due to coupling between a 30nm thin permalloy (Py) nanodisk with diameters from 250-1000nm and a multilayer Ir/Co/Pt film with strong DMI. Using element-specific magnetic soft x-ray microscopy we were able to image the magnetic structure of the Py nanomagnets and the spin texture in the DMI film independently. We found a significant increase of the imprinted domain period (240nm) in the film under the disks compared to the free film (180nm), which can be traced back to a locally varying stray field energy. We stabilize extended target skyrmions in the film with up to four π rotations of the z component of magnetization. This is due to the reduced stray field energy and enforced radial symmetry caused by the Py disk. We confirm that these structures have a uniform chirality enforced by the DMI of the thin film by observing an asymmetric expansion of the domain walls as a function of applied magnetic field pulses. We also observe the overall structural stability of target skyrmions in an external magnetic field has no dependence on topological charge.