Direct observation of attractive skyrmions and skyrmion clusters in the cubic helimagnet Cu2OSeO3

We report the discovery of attractive magnetic skyrmions and their clusters in noncentrosymmetric ferromagnets. These three-dimensional solitons have been predicted to exist in the cone phase of chiral ferromagnets [J. Phys: Condens. Matter 28, 35LT01 (2016)] and are fundamentally different from the more common repulsive axisymmetric skyrmions that occur in the magnetically saturated state. We present real-space images of these skyrmion clusters in thin (∼70 nm) single-crystal samples of Cu2OSeO3 taken using transmission electron microscopy and develop a phenomenological theory describing this type of skyrmion.