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

[摘要] We report on THz absorption spectroscopy combined with high magnetic fields of polycrystalline RCrO3 (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 Cr3+ 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 4f moment and ion size. We also studied temperature and field dependence of crystal field levels in the same spectroscopic region. Pr3+ non-Kramers emerges at 100 K and Zeeman splits. An observed absence of spin wave resonances in PrCrO3 is attributed to Pr3+ remaining paramagnetic. In SmCrO3 near cancelation of the spin and orbital moments is proposed as the possible reason for not detecting Sm3+ 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 ErCrO3 the Er a Kramers doublet becomes active at about the TSR onset. Each line further experiences Zeeman splitting under magnetic fields while an spin reversal induced by a similar to 2.5 T field, back to the Gamma(4) (F-z) from the Gamma(1) phase at 2 K, produces a secondary splitting. The 5 K AFM and FM excitations in ErCrO3 have a concerted frequency-intensity temperature dependence and a shoulder pointing to the Er3+ 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 Gamma(1) representation. Our findings have important implications on the complex interplay in the magneto-electrodynamics associated with the Rare-Earth 4f - 3d transition metal spin coupling and the structural A site instabilities in perovskite multiferroics.

[发布日期] 2018-12-15

[关键词] THz spectroscopy;Spin wave resonances;Crystal field levels;Magneto optical effects;Multiferroics