Identification of spin wave resonances and crystal field levels in simple chromites RCrO3 (R = Pr, Sm, Er) at low temperatures in the THz spectral region

Abstract We report on THz absorption spectroscopy combined with high magnetic fields of polycrystalline RCrO 3 (R = Pr, Sm, Er) aiming understanding spin wave resonances at their low temperature magnetic phases. Our measurements show that the temperature , and the implicit anisotropies at which the Cr 3+ spin reorientation at T SR takes place, are determinant on the ferromagnetic-like (FM) and the antiferromagnetic-like (AFM) spin modes being optically active. It is found that they are dependent on Rare Earth 4 f moment and ion size. We also studied temperature and field dependence of crystal field levels in the same spectroscopic region. Pr 3+ non-Kramers emerges at 100 K and Zeeman splits. An observed absence of spin wave resonances in PrCrO 3 is attributed to Pr 3+ remaining paramagnetic. In SmCrO 3 near cancelation of the spin and orbital moments is proposed as the possible reason for not detecting Sm 3+ ground state transitions. Here, the FM and AFM resonant modes harden when the temperature decreases and split linearly under applied fields at 5 K and below. In ErCrO 3 the Er 3+ Kramers doublet becomes active at about the T SR onset. Each line further experiences Zeeman splitting under magnetic fields while an spin reversal induced by a ∼2.5 T field, back to the Γ 4 (F z ) from the Γ 1 phase at 2 K, produces a secondary splitting. The 5 K AFM and FM excitations in ErCrO 3 have a concerted frequency-intensity temperature dependence and a shoulder pointing to the Er 3+ smaller ion size also disrupting the two magnetic sublattice approximation. Both resonances reduce to one when the temperature is lowered to 2 K in the Γ 1 representation. Our findings have important implications on the complex interplay in the magneto-electrodynamics associated with the Rare-Earth 4 f – 3d transition metal spin coupling and the structural A site instabilities in perovskite multiferroics.