Magnetic memory devices that use electron spin as magnetic information have attracted attention as next-generation devices with high reading/writing speed and non-volatility. The skyrmion, an electron spin vortex, can be driven with lower current density than that for driving the conventional ferromagnetic domain walls (the boundaries between domains where electron spin is aligned). It is because that skyrmion can avoid pinning sites (such as crystal defects) when it moves under electric current, different from the magnetic domain walls in ferromagnets.
One skyrmion with topological charge of 1 acts as one information bit. However, while a skyrmion which carries a higher topological charge has been predicted theoretically, but had yet to be demonstrated experimentally.
The research group of Professor Yoshinori Tokura at the University of Tokyo Graduate School of Engineering has succeeded in creating a skyrmion molecule with topological charge of 2 in the (001)-plane plate of bilayered manganite La2-2xSr1+2xMn2O7 (x = 0.315) for the first time. Such a skyrmion molecule has been driven successfully with three orders of magnitude lower current density (<108 Am-2) than that for conventional ferromagnetic domain walls. Such findings will bring about great development in designing novel magnetic memory devices with high-density and low power consumption using skyrmions.
The main component of this research was achieved in the “Quantum Science on Strong Correlation” project (Core Researcher: Yoshinori Tokura) of the FIRST program. The research result was obtained in collaboration with RIKEN-CEMS (Director: Yoshinori Tokura) and Advanced Key Technologies Division (Division Director: Daisuke Fujita) at NIMS.
Source: University of Tokyo