Force-driven control of individual magnetic skyrmions on Fe/Ir(111) with atomic force microscopy

抄録

Magnetic skyrmions, shown in Fig. 1(a), are noncollinear magnetic structures. They are stable despite their nanometer scale size because they are topologically protected. Besides, they can be driven easily with small currents [1]. With these properties, they are promising for applications for memory technologies such as racetrack memories [2]. It is necessary to write and delete individual magnetic skyrmions for this application. This was achieved with spin-polarized current, electric field and magnetic field gradient [3, 4, 5]. As the information density should increase in the next generation memories, more localized methods for manipulation will be preferred. We focused on external force as a local means of manipulation. The aim of the present study is to control magnetic skyrmions with external force and to quantify it.

Individual magnetic skyrmions appear on Fe/Ir(111) when external magnetic fields are applied [4]. In the present study, local external force was applied to individual magnetic skyrmions on Fe/Ir(111) by bringing atomic force microscopy (AFM) tips closer to them. When an external magnetic field was applied to Fe/Ir(111), an individual magnetic skyrmion was observed with scanning tunneling microscopy (STM), as shown in Fig. 1(b). It had a bean-like shape, similar to those seen in the previous study [3]. The AFM tip was brought closer to the sample surface, and this resulted in annihilation of the magnetic skyrmion. Forces acting between the tip and the sample during the tip approach and the tip retraction were measured. The measurement clarified that they are different before and after the annihilation. In this presentation, we discuss what kind of force is acting between the tip and the sample during the annihilation to reveal the origin of the skyrmion annihilation. In addition, the creation and annihilation mechanism of individual magnetic skyrmions proposed in the previous research will be compared.

[1] N. Nagaosa and Y. Tokura, Nat. Nanotechnol. 8, 899 (2013). [2] A. Fert, V. Cros and J. Sampaio, Nat. Nanotechnol. 8, 152 (2013). [3] N. Romming et al., Science 341, 636 (2013). [4] P.-J. Hsu et al., Nat. Nanotechnol. 12, 123 (2017). [5] A. Casiraghi et al., Commun. Phys. 2, 145 (2019).