Fig. 1. Cold all-optical toggle switching of magnetization.

a (left panel) Magnetic domain pattern, where initially the magnetization can be either in the [11−1] state (black domain) or in the [1−11] state (white domain). Schematic illustration of the magnetic switching between [11−1] and [1−11] in iron garnet (right panel). b Magneto-optical images of Co-substituted yttrium iron garnet (YIG:Co) after illumination with a series of pump pulses. The fluence of a single laser pulse is 50 mJ/cm². The central wavelength of the laser is 1300 nm. The pump is linearly polarized along the [100] crystallographic axis. Dashed circles indicate the area exposed to the laser excitation. Small solid circles indicate the region, where the measurements of the magneto-optical Faraday effect shown in (a) were done. c Differential magneto-optical images obtained as the difference between the images after $n$-th and $\left(n-1\right)$-th pump pulses. The images reveal the toggle switching. As the switched states were captured as static images, the remaining ring on the switched spot’s edge results from a domain wall motion on a much longer (microsecond) time-scale, as also observed in metallic alloys⁹. d Changes of the Faraday rotation in the black domain upon excitation by a sequence of laser pulses. Every single pulse changes the magneto-optical effect suggesting that the magnetization is toggled between two stable bit-states.