Photoinduced Switching of Magnetization in the Epsilon-Near-Zero Regime

Midinfrared laser pulses tuned to optical phonon frequencies can induce magnetization switching in magnetic dielectrics, but the underlying mechanisms remain unclear, since excitations of the crystal lattice can simultaneously produce heating and nonthermal strain. Here, we study the response of labyrinthine magnetic domains in a cobalt-doped yttrium iron garnet film to midinfrared pulses. We observe a transformation of the labyrinthine domains into stable parallel stripes, which micromagnetic calculations can explain through a partial quenching of the magnetic anisotropy. Surprisingly, the efficiency of this thermally driven process of switching is spectrally strongest not at the maximum of absorbed optical energy, but rather at the epsilon-near-zero (ENZ) points. Electromagnetic calculations show that, in this regime, the optical field penetrates the film more uniformly, leading to homogeneous energy deposition across the magnetic layer. Our results demonstrate that magnetization switching can be controlled through engineering of the optical field distribution via the ENZ condition, which optimally shapes the spatial profile of optical absorption.