Optical detection of magnetic orders in HgCr₂O₄ frustrated spin magnet under pulsed high magnetic fields

A magneto-optical survey was conducted for HgCr$_2$O$_4$ powder samples under pulsed high magnetic fields of up to 55 T. Intensity changes in magnetic fields observed for the exciton-magnon-phonon optical transition spectra coincide well with those of magnetization, lattice distortion from X-ray diffraction, and electron-magnetic resonances. The last-ordered phase was detected prior to the fully polarized magnetic phase, similarly to the other chromium spinel oxide, ZnCr$_2$O$_4$ and CdCr$_2$O$_4$.