Ultrafast Helicity-Dependent Magnetic Switching by Optical Phonons Driven at Resonance

Using narrow-band mid- to- far-infrared circularly-polarized optical pulses, we demonstrate that magnetization can be switched all-optically in magnetic nanostructures mounted on fused-silica and sapphire substrates. The helicity-dependent magnetic switching scales in efficiency with optical phonons characteristic of the substrate. We explain the switching in terms of a transient magnetic field originating from resonantly-driven circularly-polarized lattice vibrations in the substrate.