Abstract Recently, magnetic skyrmions have been emerged as one of the promising candidates to use information carriers in high density and low power spintronic devices, which potentially be use in memory, logic, and neuromorphic computing due to their nanometer scale small size, non-volatile, and complete linearity [1-2]. Previous studies reported the observation of skyrmion sizes below 100 nm at room temperature [3-4]. However, so far, researches on the size of generated skyrmions depending on the different materials of interface reducing layer have not been discussed. In this study, therefore, we investigated the dependency of generated skyrmion size in perpendicular magnetic anisotropy (PMA) structures on the material of interface reducing layer (tungsten (W), platinum (Pt), and titanium (Ti)) to generate skyrmion. In addition, We designed a novel PMA structure having an interface reducing layer inserted in between CoFeB free layer and MgO tunnel barrier to generate skyrmions. In particular, the dependencies of the PMA characteristics, including coercivity (H c ), perpendicular anisotropy (H k ), and saturation magnetization (M s ) on the materials (W, Pt, and Ti) and thickness of interface reducing layer were investigated by using a vibrating sample magnetometer (VSM), and magneto-optical Kerr effect (MOKE). Our proposed PMA structures exhibited that H c was reduced to ~ 5 Oe at the specific thickness of interface reducing layer (W: 0.0804 nm, Pt: 0.1670 nm, Ti: 0.3602 nm), indicating that the skyrmions generated. In addition, it was confirmed that the material of the interface reducing layer strongly influences the size of skyrmions generated in a PMA structure, i.e., 0.0804-nm-thick tungsten generated the skyrmion diameter of 1.23 μm, 0.1670-nm-thick platinum generated the skyrmion diameter of 0.78 μm, and 0.3602-nm-thick titanium generated the skyrmion diameter of 0.84 μm, respectively. We present in detail how H c , H k , M s , and generated skyrmion size were affected by the material of interface reducing layer. Acknowledgements This work was supported by the Technology Innovation Program (or Industrial Strategic Technology Development Program-Public-private joint investment semiconductor R&D program(K-CHIPS) to foster high-quality human resources) ("RS-2023-00235634", Development of high speed/low power/high reliability 2-terminal field-free SOT-MRAM) funded By the Ministry of Trade, Industry & Energy (MOTIE, Korea)( 1415187787) References [1] Nagaosa N. and Tokura Y., Nat. Nanotechnol. 8, 899-911 (2013). [2] C Back, V Cros et al., J. phys. D. Appl. phys. 53, 363001 (2020). [3] Aranda A.R. et al. Journal of Magnetism and Magnetic Materials, 465, 471-479 (2018). [4] Mouad F. et al. Physics Letters A, 384(13), 126260 (2020). Figure 1