Experimental evidence of symmetry breaking in the multiferroic Ba_3NbFe_3Si_2O_(14) using sound velocity measurements

摘要

Using high-resolution sound velocity measurements, we determined the temperature dependence of the principal elastic constants of the multiferroic compound Ba_3NbFe_3Si_2O_(14) at different magnetic fields. All four elastic constants revealed an anomaly at T_N = 27.1(1) K, which coincides very well with the emergence of the magnetic chiral state. More importantly, we carried out velocity measurements as a function of a field rotating in the basal trigonal plane at different fields and temperatures. In particular, in the magnetically ordered state, we observed an angular hysteresis of ΔC_(11)/C_(11), which might be associated with the field-induced ferroelectric polarization suddenly switching from the b∗ axis to the a direction, due to the magnetoelectric effect previously observed inBa_3NbFe_3Si_2O_(14). The data analysis also leads to an estimate for the lattice distortion (e_1 − e_2 ≤ 10~(−5)) accounting for a symmetry reduction in the magnetic chiral state possibly associated with the induced polarization along the a axis in zero field.