Phase transition in Y$_3$Fe$_5$O$_{12}$ at high pressures observed by Raman spectroscopy

The vibrational properties of yttrium iron garnet Y$_3$Fe$_5$O$_{12}$ at a high quasihydrostatic pressure are studied by the Raman spectroscopy method. Raman spectra are measured in a high-pressure diamond anvil cell in the pressure range of $0$–$72$ GPa at room temperature. A fundamental change in the character of spectra with the disappearance of sharp peaks is detected near $\sim50$ GPa. This confirms a phase transition from the crystalline to amorphous state, which was previously detected by other experimental methods. This transition is accompanied by spin crossover in Fe$^{3+}$ ions, which transit from the high-spin (HS, $S = 5/2$) to low-spin (LS, $S=1/2$) state. The pressure dependences of phonon modes in Y$_3$Fe$_5$O$_{12}$ are measured from atmospheric pressure to the critical phase transition pressure.