Magnetic switching of ferromagnetic materials with a single femtosecond laser pulse

In 2007, researchers achieved a major breakthrough in ultrafast magnetism, which involves manipulating magnetic materials on a very short time-scale, by demonstrating that a single femtosecond laser pulse could reverse magnetization in the ferrimagnetic GdFeCo. However, ferromagnetic systems, which are of great interest for improving information processing, recording and other technologies, require thousands of repeated laser pulses for full switching. Multiple pulses mean lower switching speed and more input energy.

In Applied Physics Letters, researchers from California detail their innovation for reversal of magnetization in ferromagnetic materials with only a single laser pulse. Such ultrafast operation expands the range of applications that use magnetic devices. The researchers achieved full switching in a ferromagnetic Co/Pt layer a mere 7 picoseconds after irradiation with a femtosecond laser.

According to author Jon Gorchon, the trick was to grow the ferromagnetic layer on top of a layer of GdFeCo to exploit the coupling between the two materials. This configuration extends the single-shot capabilities of GdFeCo to the ferromagnet.

To verify the switching, the researchers performed hysteresis loops with a magneto optical Kerr effect (MOKE) microscope and polarizer to separate the contributions from each layer. Also, time-resolved switching experiments probed for changes in magnetization after sending femtosecond laser pulses of varying power.

The researchers indicate this method can be extended to other ferromagnets, ferrimagnets, or antiferromagnets. Because intense heat is considered the cause of the switching, Gorchon and his colleagues want to explore the possibilities of using very short electrical pulses instead of laser pulses. In the future, this type of ultrafast control could improve the density and stability of hard drive memory, while also having important implications for the field of spintronics.

Source: “Single shot ultrafast all optical magnetization switching of ferromagnetic Co/Pt multilayers,” by Jon Gorchon, Charles-Henri Lambert, Yang Yang, Akshay Bhimesh Pattabi, Richard Wilson, Sayeef Salahuddin, and Jeffrey Bokor, Applied Physics Letters (2017). The article can be accessed at https://doi.org/10.1063/1.4994802 .