DiscussionA semi-skyrmions-based oscillator in elliptical nanopillars with perpendicular anisotropy
Introduction
Magnetic skyrmions have recently aroused the interest of many scientists and technicians because of its numerous topological physical properties, such as topological Hall effect [1], [2], [3], [4], skyrmions Hall effect [5], [6], spin orbital torque [7], [8], etc. Previous studies have shown that as an information carrier, magnetic skyrmions have significant advantages: small size, low critical driving current, good stability and so on [9], [10], [11]. Therefore, Skyrmions have potential application prospects in the research and development of high density and low energy consumption memory. In theory, skyrmions have also been proved to be applicable to transistors [12], logic devices [13], and spin-torque nano-oscillator (STNO) [14], [15], [16], [17]. In addition, the shape and motion of skyrmions can be driven not only by current, but also by static magnetic field [18], [19], [20], microwave magnetic field [21], [22], magnetic field gradients [23], spin wave and electric field [24], [25]. The diversification of manipulation means greatly expanding the application prospects of skyrmions.
The STNO has the advantages of small size, wide frequency modulation range, low power consumption and easy integration [26]. Garcia-Sanchez et al. have reported the skyrmions STNO with different polarization layers [15]. The skyrmions-based STNO driven by point current and the nano-oscillator array based on the repulsion between the domain wall and magnetic skyrmion are also proposed [14], [17]. It is mentioned in reference [14] that the oscillation frequency of the STNO with multiple magnetic skyrmions is higher than that of the STNO with a single magnetic skyrmion oscillator. In this paper, we show the dynamics of magnetic skyrmions in elliptical spin-valve nanopillar with PMA free layer and spin polarizer [27], [28]. The STNO with semi-skyrmions behaviors at GHz frequencies are observed in this geometry. Based on this semi-skyrmion behavior, we put our research on the frequency of the semi-skyrmions oscillation.
Section snippets
Model and simulation details
Our studied elliptical spin-valve nanopillar consists of a PMA free layer and a PMA spin polarizer, as illustrated in Fig. 1(a). Micromagnetic simulations were performed by using a finite-difference code based on the MuMax3 program [29], which employs the Landau-Lifshitz-Gilbert-Slonczewski (LLGS) equation with the Dzyaloshinskii-Moriya interaction (DMI) [29], [30]. In the simulations, the positive current is defined as electrons flowing from the polarizer to the free layer. The saturation
Results and discussion
First, the simulations are performed in an elliptical spin-valve nanopillar with the free layer thickness , major axis , and minor axis . The simulation time is set as 20 ns, which is enough for observing the stable spin texture in the free layer. Fig. 1(b) shows the typical spin texture observed in the free layer including stripe, skyrmion, and semi-skyrmion states. Previous studies have shown that skyrmion will have a velocity perpendicular to the current direction due to
Conclusions
In summary, we show the dynamics of the semi-skyrmions oscillation in elliptical spin-valve nanopillar with PMA free layer and spin polarizer. Two semi-skyrmions move along the edge of the sample in the counterclockwise (CCW) direction, which generates a GHz frequency. The simulation results show that the semi-skyrmion oscillation frequency is strongly depend on the in-plane dimension of the elliptical nanopillar, and is also affected by the material parameters including damping constant α,
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This work was supported by the Opening Project of Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology, the National Natural Science Foundation of China (NSFC) Grant Nos. 51971161, 51302157, and the funding for first-class discipline from Shandong Agricultural University.
References (35)
Current-driven excitation of magnetic multilayers
J. Magn. Magn. Mater.
(1996)- et al.
Phys. Rev. B
(2009) - et al.
Phys. Rev. Lett.
(2009) - et al.
Phys. Rev. Lett.
(2011) - et al.
Nat. Phys.
(2016) - et al.
Nat. Mater.
(2016) - et al.
Nat. Phys.
(2016) - et al.
Science
(2012) - et al.
Nat. Phys.
(2012) - et al.
Phys. Rev. B
(2013)
Proc. IEEE
IEEE Electron Device Lett.
Sci. Rep.
Sci. Rep.
New J. Phys.
New J. Phys.
AIP Adv.
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