Phonons and magnetic excitation correlations in weak ferromagnetic YCrO_3

摘要

Here, we report the temperature dependent Raman spectroscopic studies on orthorhombically distorted perovskite YCrO_3 over a temperature range of 20-300 K. Temperature dependence of DC-magnetization measurements under field cooled and zero field cooled protocols confirmed a Neel transition at T_N～142K. Magnetization isotherms recorded at 125 K show a clear loop opening without any magnetization saturation up to 20kOe, indicating a coexistence of antiferromagnetic (AFM) and weak ferromagnetic (WFM) phases. Estimation of exchange constants using mean-field approximation further confirm the presence of a complex magnetic phase below T_N. Temperature evolution of Raman line-shape parameters of the selected modes (associated with the octahedral rotation and A(Y)-shift in the unit-cell) reveal an anomalous phonon shift near T_N. An additional phonon anomaly was identified at T~* ～ 60 K, which could possibly be attributed to the change in the spin dynamics. Moreover, the positive and negative shifts in Raman frequencies between T_N and T~* suggest competing WFM and AFM interactions. A close match between the phonon frequency of B_(3g) (3)-octahedral rotation mode with the square of sublattice magnetization between T_N and T~* is indicative of the presence of spin-phonon coupling in multiferroic YCrO_3.