Enhanced thermally-activated skyrmion diffusion in synthetic antiferromagnetic systems with tunable effective topological charge

Magnetic skyrmions, topologically-stabilized spin textures that emerge in particular magnetic systems, have attracted attention due to a variety of electromagnetic responses that are governed by the topology. A well-studied effect of topology on the deterministic and drift motion under a nonequilibrium excitation is the so-called skyrmion Hall effect. For stochastic diffusive motion, the effect of topology is expected to have a drastically stronger impact, but the predicted even qualitative impact has not been demonstrated. The required tuning of the topology to achieve zero effective topological charge can be achieved using antiferromagnetic skyrmions. However, the diffusive motion has previously not been observed due to strong pinning in ferrimagnets and intrinsic antiferromagnets. Here we demonstrate enhanced thermally-activated diffusive motion of skyrmions in a specifically designed synthetic antiferromagnet where the topology can be tuned. Suppressing the effective topological charge for synthetic antiferromagnetic skyrmions leads to a more than 10 times enhanced diffusion coefficient as compared to ferromagnetic skyrmions. By varying the topology, we can not only demonstrate the topology-dependence of the diffusion coefficient but also enable ultimately energy-efficient unconventional computing that is actively making use of the stochasticity.