Experimental evidence of symmetry breaking in the multiferroic Ba3NbFe3Si2O14 using sound velocity measurements

Abstract

Using high-resolution sound velocity measurements, we determined the temperature dependence of the principal elastic constants of the multiferroic compound Ba 3 NbFe 3 Si 2 O 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 C 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 in Ba 3 NbFe 3 Si 2 O 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.

Spin-wave directional anisotropies in antiferromagnetic Ba3NbFe3Si2O14

“…Given the underlying nuclear structure, the magnetic spins form a single domain chiral spin pattern below T N . [31,32] The original papers discussing the magnetic structure [33] defined two terms to characterize the magnetic structure -helicity and chirality. The helicity was used to define the orientation of Fe 3+ moments on neighboring planes and is fixed through competing symmetric exchange interactions with J ∼ 1 meV.…”

Field-induced double spin spiral in a frustrated chiral magnet

“…As we see, the onset field of the δ-modulation is found to perfectly match the occurrence of the second component of the pyroelectric current and relates to the inflection points in the net polarization. We note that this transition can also be identified by an anomaly of the elastic constants [31].…”