Ultrafast control of lattice strain via magnetic circular dichroism

Using ultrafast x-ray diffraction, we directly monitor the lattice dynamics induced by femtosecond laser pulses in nanoscale thin films of bismuth iron garnet in external magnetic fields ${H}_{\mathrm{ext}}$. We control the ultrafast laser-induced lattice strain amplitude by changing the laser pulse helicity. The strength of ${H}_{\mathrm{ext}}$ is used as an external parameter to switch the helicity dependence on and off, respectively. Based on magneto-optical spectroscopic measurements, we explain these phenomena by magnetic circular dichroism. Our findings highlight an important approach for ultrafast manipulation of lattice strain in magnetic materials, in particular insulators, and open exciting perspectives towards ultrafast control of lattice strain and heat-induced magnetization switching and spin waves in bismuth substituted iron garnets using the polarization of light.