Skyrmions in magnetic thin film heterostructures

Abstract

Magnetic skyrmion is expected to function as an ideal information carrier for ultra-high density magnetic storage and logic functional device in the future due to its superior properties, such as topological protection, small size, and low driving current density for motion. In order to meet the basic requirements for writing and reading information in devices, one needs to be able to accurately generate, manipulate, and probe skyrmion at room temperature. Given that the history and latest developments of the skyrmion research will be reviewed comprehensively in other articles, in order to avoid repetition, in this article we briefly review a series of recent research advances we have made in magnetic multilayer materials in recent years, and discuss the advantages of relevant device applications and problems that need to be solved. They are included in three aspects as follows. 1) The room temperature skyrmion was observed in a wedge film Ta (5 nm)/Co20Fe60B20 (CoFeB) (1 nm)/Ta (t)/MgO (2 nm)/Ta (2 nm) by a polar magneto-optical Kerr microscope. Results showed that skyrmion can be created at room temperature by controlling the perpendicular magnetic anisotropy of magnetic thin film. In the following, we designed a thin film heterojunction containing an antiferromagnetic layer IrMn. The introduction of antiferromagnetic material can produce an exchange bias field in the magnetic layer, which can play the same role as an external magnetic field, making it possible to realize zero-field skyrmion. In this study, we have successfully observed a stable skyrmion at room temperature and zero magnetic field. 2) The spin-orbit torque generated by the current proved to be able to be used to manipulate the created skyrmion. In the fourth part of this review, we discuss the dynamic process of skyrmion driven by spin-orbit torque in IrMn/CoFeB heterojunctions, and the chirality of skyrmion can be deduced by the direction of its longitudinal motion driven by an applied current. Finally, a principle device based on the skyrmion is further fabricated. In this device, a set of binary data was recorded in the track in the presence and absence of skyrmion. Generating and manipulating numbers of skyrmions were realized by using a series of pulse currents with different amplitudes and widths. The detection of a skyrmion can be achieved by using a magnetic tunnel junction at the right end of the device. 3) The advantages of skyrmion as a storage device and the problems that need to be solved for practical applications were discussed.