Magnetic interaction effects in the temperature- and magnetic field-dependent Raman spectra 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 antiferromagnet 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. We discuss the dependence of the observed Raman-active phonons and magnons in b-cut ErFeO₃ on polarization, temperature, and magnetic field. At low temperature (T ~ 1.6K) and magnetic field H || c, the Er³⁺ electron paramagnetic resonance couples with an Fe³⁺ quasi-ferromagnetic magnon demonstrating an anti-crossing behavior. Furthermore, we compare our Raman spectra with THz measurements to further elucidate the nature of magnetic interactions in this system. [1] X. Li et al., Science 361, 794 (2018).