Recently, a team led by Prof. DU Haifeng from High Magnetic Field Laboratory, Chinese Academy of Sciences (CHMFL) directly observed a zero-field twofold degenerate target skyrmion in a chiral magnetic nanodisk by using off-axis holography. They further show that its polarity can be switched by using an applied magnetic field.

This work was published in Physical Review Letters entitled "Direct Imaging of a Zero-Field Target Skyrmion and Its Polarity Switch in a Chiral Magnetic Nanodisk", and was simultaneously reported in American Physical Society's website Physics.

The target skyrmion was first predicted by DU in 2013. However, because the size of nanodisk to realize target skyrmion is about 100 nanometers and very high magnetic solution (<5 nm) for the setup is necessary, it is a challenge to perform the experiment.

Based on the accumulation of nanostructure preparation technique over past few years, the team overcame the obstacles by using focused ion beam technique to fabricate a 160-nanometer-wide, 90-nanometer-thick FeGe disk.

They further used the advanced off-axis electron holography microscopy in Germany to observe the magnetic structure in such small disk.

And finally they directly imaged the target skyrmion and discovered that its polarity could be switched by using an applied magnetic field.

The numerical calculation performed by group in USA also identified the stabilization and switch mechanism of target skyrmions.

This work provides a solid physical basis for future skyrmion-based applications such as logic gates or as magnetically controlled switches in nano-devices.

This study was conducted by DU's team collaborated with Prof. ZANG Jiadong from University of New Hampshire, USA, and Prof. Rafal E. Dunin-Borkowski from Forschungszentrum J lich, Germany.

The work was supported by the National Key R&D Program of China, the Key Research Program of Frontier Sciences, CAS, the Key Research Program of CAS, Natural Science Foundation of China, the Youth Innovation Promotion Association, CAS, and Collaborative Innovation Center of Advanced Microstructure, Nanjing University.

Imaging of a zero-field target skyrmion and its polarity switching by using off-axis electron holography technique.si