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

Abstract

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 ηSk, determined by Lorentz TEM observation, reaches 60 μm−2 in [Pd(3)/Co(1)/Pd(2)]15 multilayer film. We also found that the maximum density ηSk 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.