Temperature- and magnetic field-dependent Raman spectroscopy of ErFeO₃

The recent report[1] of Dicke cooperativity in the magnetic interactions of erbium orthoferrite ErFeO₃ as observed in terahertz (THz) spectra stimulates a complementary Raman spectroscopic study. Bulk ErFeO₃ forms an orthorhombic perovskite crystal structure (space group Pbnm) and demonstrates antiferromagnetic ordering of the Fe³⁺ spins below the Néel temperature T_N ~ 650K, with additional magnetic phases occurring below 85K. A novel, magneto-Raman microscope system affords measurement of low-frequency (down to ~10cm^-1) Raman-active lattice (phonons) and magnetic (magnons) excitations as a function of polarization orientation, temperature (2 to 300)K, and magnetic field (0 to 9)T in Faraday and Voigt geometries. A combination of polarized Raman and Laue x-ray diffraction determines the crystallographic axes. We discuss the dependence of the observed Raman-active phonons and magnons in b-cut ErFeO₃ on polarization, temperature, and magnetic field, specifically, low-temperature and H-field || a-axis. Furthermore, we compare our Raman spectra with THz measurements to further elucidate the nature of magnetic interactions in this material.

[1] X. Li et al., Science 361, 794 (2018).