Magnetization dynamics in a 2D van der Waals ferromagnet

Two-dimensional van der Waals semiconductors possess certain advantages over traditional epitaxially grown semiconductors for spintronics applications. In particular, the thickness of these structures can be mechanically manipulated with monolayer accuracy, which proves useful for controlling their layer-dependent intrinsic ferromagnetism. Such 2D ferromagnets have shown unique properties for fundamental research and device applications.

Zhang et al. decided to investigate an unanswered question in the development of 2D magnet-based storage devices. What are the magnetization dynamics of a van der Waals magnet down to the 2D limit? In theory, how fast can one of these 2D magnets achieve read or write operation? To begin this project, they studied the magnetization dynamics of a van der Waals semi-insulating Cr₂Ge₂Te₆ nanoflake at cryogenic temperature.

For the experiment, the researchers developed a two-color, time-resolved Faraday rotation technique with an ultrafast time resolution of 1 picosecond. The technique also offers micrometer lateral resolution to separately study 2D magnets of a very small size, something not easily accomplished with the usual method of ferromagnetic resonance.

From the laser-induced magnetization dynamics, the scientists determined that the perpendicular magnetic anisotropy of the Cr₂Ge₂Te₆ nanoflake is 125 millitesla at 10 degrees Kelvin. They also found an intrinsic Gilbert damping constant as small as 0.006, which is clearly lower than most ferromagnet materials with perpendicular magnetic anisotropy. Such a small Gilbert damping constant indicates a weak energy dissipation during the magnetization operation process.

The results suggest semi-insulating van der Waals ferromagnets may be promising candidates for low-dissipation magnetic devices, such as spin-transfer torque magnetic random-access memory.

Source: “Laser-induced magnetization dynamics in a van der Waals ferromagnetic Cr₂Ge₂Te₆ nanoflake” by Tongyao Zhang, Yuansen Chen, Yanxu Li, Zhichao Guo, Zhi Wang, Zheng Han, Wei He, and Jing Zhang, Applied Physics Letters (2020). The article can be accessed at http://doi.org/10.1063/5.0006080 .