Manipulation of topological spin textures in centrosymmetric rare-earth magnets

•Biskyrmions in Nd1–xTbxCo5 alloy were directly observed and manipulated by in-situ LTEM.•Biskyrmions can spontaneously exist at room temperature in Nd1–xTbxCo5 alloy.•A strategy to control biskyrmion nucleation via the in-plane magnetic field was proposed.•High-density biskyrmions were obtained by tuning the magnetic field.•Key factors for stabilizing spontaneous topological spin textures were revealed.