Temperature-Dependent Structural, Dielectric, and Raman Spectroscopy Studies on Magnetoelectric Co<sub>4</sub>Nb<sub>2</sub>O<sub>9</sub>
Satish Yadav, Mohit Chandra, R. Rawat, Ashish Khandelwal, L. S. Sharath Chandra, R. J. Choudhary, Vasant Sathe, A. K. Sinha, Kiran Singh
Abstract
Co4Nb2O9 (CNO) is one of the interesting magnetoelectric materials. Here, we report comprehensive temperature-dependent structural, phonon, dielectric, and magnetic properties of CNO. In contrast to most of the earlier reports, a clear transition (upturn feature) is observed in temperature-dependent dielectric measurements at the antiferromagnetic ordering (TN) ∼27.2 K, even in the absence of magnetic field. The upturn-like feature at TN (in zero magnetic field) becomes a sharp peak above the critical magnetic field. The isothermal magnetodielectric (MD) results infer magnetic field-induced transition below TN with nonlinear behavior. The maximum MD effect (∼4%) is observed at TN at 80 kOe. The terahertz measurements exhibit spin excitation mode below TN in the absence of magnetic field. The temperature-dependent synchrotron X-ray diffraction results demonstrate that the crystal structure of CNO remained P3̅c1 down to 12 K; however, small distortion in the lattice is observed at TN. The temperature-dependent Raman measurements infer an unusual phonon shift and line width of optical phonons below TN. These results illustrate that CNO exhibits dielectric transition even in the absence of magnetic field and exhibit magnetoelastic coupling. The correlation in these order parameters is also discussed.