Room-temperature zero field and high-density skyrmions in Pd/Co/Pd multilayer films

Magnetic skyrmions are topological chiral spin textures, which have potential application in storage-memory and other spintronic devices. Zero-field skyrmion and high-density skyrmion are the two most important aspects for the future skyrmion-based device applications. Here, we experimentally study the room temperature zero-field skyrmion and the evolution of high density skyrmion in [Pd/Co/Pd](N) multilayer films from structure symmetry to asymmetry. The results show that the density of zero-field skyrmion can be adjusted by the number of cycles at the constant thickness of Co 0.4 nm. The maximum density eta(Sk), determined by Lorentz TEM observation, reaches 60 mu m(-2) in [Pd(3)/Co(1)/Pd(2)](15) multilayer film. We also found that the maximum density eta(Sk) mainly occur in the reversible region of magnetization reversal by the first-order reversal curve (FORC) analysis. Interestingly, the polarity of zero-field skyrmion can be tuned by different MFM tips. The simulated results well confirm the experimental result. Our findings provide a pathway for designing the zero-field and high density skyrmion in magnetic multilayer films, which may apply for the development of skyrmion-based spintronic devices.