Symmetry breaking and spin lattice coupling in NdCrTiO5

The origin of multiferroicity in NdCrTiO5 has been examined. A first-order phase transition, due to breaking of the inversion symmetry, near the lowerature antiferromagnetic ordering (TN∼21 K) where spontaneous electric polarization also appears, is confirmed. From synchrotron x-ray powder diffraction measurements, the structure at low temperatures is found to be noncentrosymmetric (space group Pba2), justifying the polar behavior of this compound below TN. Temperature-dependent Raman measurements reveal that the lattice is strongly coupled with the spins, pointing to the spin lattice correlations in a noncentrosymmetric space group being responsible for invoking the ferroelectricity below 21 K. Through time-of-flight neutron powder diffraction experiments, it is confirmed that the magnetic sublattices, both Nd and Cr, simultaneously order at TN, and at temperatures below 15 K the Cr moments are found to be saturated while the Nd moments continue to grow until 6 K.