Laser-induced excitation and decay of coherent optical phonon modes in an iron garnet

Abstract

The excitation of optical phonon modes at resonance has been recently identified as offering a promising energy-efficient pathway for the ultrafast switching of magnetization. Here, using time-resolved pump–probe measurements, we explore the characteristics of different optical phonon modes in ferrimagnetic cobalt-doped yttrium iron garnet. By rotating the linear polarization of both the pump and probe, we identify a large spectrum of optical phonons within the frequency band of 3–11 THz. We determine the lifetimes of the different phonons using band filtration, revealing that the phonon mode with the eigenfrequency 3.4 THz survives for up to 13 ps. Its long lifetime, comparable with the relaxation time of photo-magnetic anisotropy in garnets, renders this phonon mode the most promising candidate for ultrafast phononic switching of magnetization.