Spatial control of skyrmion stabilization energy by low-energy Ga+ ion implantation

Author:

Miki S.123ORCID,Hashimoto K.123,Cho J.4ORCID,Jung J.5ORCID,You C. Y.5ORCID,Ishikawa R.6ORCID,Tamura E.123,Nomura H.123ORCID,Goto M.123ORCID,Suzuki Y.123

Affiliation:

1. Graduate School of Engineering Science, Osaka University 1 , Toyonaka, Osaka 560-8531, Japan

2. Spintronics Research Network Division, Institute for Open and Transdisciplinary Research Initiatives, Osaka University 2 , Suita, Osaka 565-0871, Japan

3. Center for Spintronics Research Network (CSRN), Graduate School of Engineering Science, Osaka University 3 , Toyonaka, Osaka 560-8531, Japan

4. Division of Nanotechnology, Daegu Gyeongbuk Institute of Science and Technology (DGIST) 4 , Daegu 42988, South Korea

5. Department of Physics and Chemistry, Daegu Gyeongbuk Institute of Science and Technology (DGIST) 5 , Daegu 42988, South Korea

6. ULVAC-Osaka University Joint Research Laboratory for Future Technology, Osaka University 6 , Suita, Osaka 565-0871, Japan

Abstract

Magnetic skyrmions are candidates for information carriers in Brownian and stochastic computers. Developing a technique for fabricating a film with a suitable potential landscape, wherein the information carrier may diffuse freely, is essential for these probabilistic computers. In this study, to build the desired local potential into magnetic films, a 1.2 nm-thick Co-Fe-B film with a 5.2 nm-thick cap layer was irradiated by a focused ion beam (FIB) using Ga+ as the ion source under a low acceleration voltage of 5 keV. The fluences ranged from 0 to 25 × 1012 ions/cm2. Consequently, the critical temperature at which skyrmions appear or disappear is shifted by several 1–10 K depending on the ion fluence. The origin of this effect is discussed by observing the ion implantation profile and the surface sputtering depth using time-of-flight secondary ion mass spectrometry (TOF-SIMS) and atomic force microscopy (AFM). The results of TOF-SIMS measurements show that most of the Ga atoms exist in the Co–Fe–B layer. If all Ga atoms exist in the Co–Fe–B layer, the Ga concentration is 7 × 10−3 at. % after irradiation of 0.8 × 1012 ions/cm2. The AFM results show a sputtered pattern with 0.2 nm depth after irradiation of 16 × 1012 ions/cm2. Finally, the effect of irradiation on the diffusion coefficient was examined. It was determined that small fluences of 1.6 × 1012 and 0.8 × 1012 ions/cm2 can construct a potential barrier controlling skyrmions while maintaining diffusion coefficients as high as 10 μm2/s. The FIB process can be used to draw a circuit of probabilistic computers with skyrmions as information carriers.

Funder

Japan Society for the Promotion of Science

Core Research for Evolutional Science and Technology

Nanotechnology Platform of MEXT

National Research Foundation of Korea

ULVAC, Inc The Center for Spintronics Research Network (CSRN), Graduate School of Engineering Science, Osaka University

Publisher

AIP Publishing

Subject

Physics and Astronomy (miscellaneous)

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