Deformation of Néel-type skyrmions revealed by Lorentz transmission electron microscopy

Journal Article · Mon Apr 06 04:00:00 EDT 2020 · Applied Physics Letters

DOI:https://doi.org/10.1063/5.0002592· OSTI ID:1633276

Zhang, Senfu ^[1]; Zhang, Junwei ^[2]; Wen, Yan ^[1]; Peng, Yong ^[3]; Qiu, Ziqiang ^[4]; Matsumoto, Takao ^[5]; Zhang, Xixiang ^[1]

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1. King Abdullah University of Science and Technology (KAUST), Thuwal (Saudi Arabia)
2. King Abdullah University of Science and Technology (KAUST), Thuwal (Saudi Arabia); Lanzhou University, Lanzhou (China). Key Laboratory for Magnetism and Magnetic Materials of Ministry of Education
3. Lanzhou University, Lanzhou (China). Key Laboratory for Magnetism and Magnetic Materials of Ministry of Education
4. Univ. of California, Berkeley, CA (United States)
5. Univ. of Tokyo (Japan). Institute of Engineering Innovation

Néel-type magnetic skyrmions in multilayers are promising candidates for ultra-low power spintronic devices. To image the Néel-type skyrmions using Lorentz transmission electron microscopy (L-TEM), the samples must be tilted. Thus, the external magnetic field consists of both in-plane and out-of-plane components. To date, it is still not well known on the effect of the in-plane magnetic field on the L-TEM images, leading to ambiguities in retrieving the structure of Néel-type skyrmions. Here, Néel-type skyrmions in three [Pt/Co/Ta]$$_{20}$$ multilayer samples, with the easy magnetization axis being tuned from the out-of-plane to the in-plane direction by increasing the Co thickness from 1.8 to 2.2 nm, are imaged. When using a smaller defocus value (-2 mm) and a higher magnification (×9100) of L-TEM, a surprising dark-bright-dark-bright double contrasted pattern, instead of the previously reported dark-bright contrasted pattern, is observed. The additional dark-bright contrasted pattern becomes more evident for thicker Co layer samples in which the magnetization axis tilts more toward the in-plane direction. Further analysis, via a combination of magnetic force microscopy experiments, micromagnetic simulations, and micromagnetic analysis to Lorentz TEM simulation, shows that the additional dark-bright features originate from the deformation of the Néel-type skyrmions within an in-plane magnetic field.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES). Materials Sciences & Engineering Division; King Abdullah University of Science and Technology (KAUST), Office of Sponsored Research (OSR); National Natural Science Foundation of China (NNSFC)
• Grant/Contract Number: AC02-05CH11231
• OSTI ID: 1633276
• Journal Information: Applied Physics Letters, Journal Name: Applied Physics Letters Journal Issue: 14 Vol. 116; ISSN 0003-6951
• Publisher: American Institute of Physics (AIP)
• Country of Publication: United States
• Language: English

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