Temperature-Dependent Structural, Dielectric, and Raman Spectroscopy Studies on Magnetoelectric Co₄Nb₂O₉

Abstract

Co 4 Nb 2 O 9 (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 (T N ) ∼27.2 K, even in the absence of magnetic field. The upturn-like feature at T N (in zero magnetic field) becomes a sharp peak above the critical magnetic field. The isothermal magnetodielectric (MD) results infer magnetic field-induced transition below T N with nonlinear behavior. The maximum MD effect (∼4%) is observed at T N at 80 kOe. The terahertz measurements exhibit spin excitation mode below T N in the absence of magnetic field. The temperature-dependent synchrotron X-ray diffraction results demonstrate that the crystal structure of CNO remained P3̅ c1 down to 12 K; however, small distortion in the lattice is observed at T N . The temperature-dependent Raman measurements infer an unusual phonon shift and line width of optical phonons below T N . 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.

Magnetoelastic Coupling Evidence by Anisotropic Crossed Thermal Expansion in Magnetocaloric RSrCoFeO6 (R = Sm, Eu) Double Perovskites

“…Anomalies in the structural parameters near the magnetic transition temperature are generally associated with the presence of a magnetoelastic coupling − , and require a detailed investigation to understand and clarify this correlation. The R/Sr–O (R = Sm, Eu) and Co/Fe–O bond distances in the crystallographic a -, b -, and c -axis directions were extracted from the refined crystal structures and are displayed in Figure S8.…”

“…To circumvent this situation, this work focuses on new disordered double-perovskite-based RSrCoFeO 6 (R = Sm, Eu) oxides, which have the potential to lead to high magnetocaloric performance with enhanced magnetic entropy changes. In these compounds, the coupling behavior between magnetism and the crystal lattice plays a crucial role, the so-called magnetoelastic effect, − manifested when magnetic ions interact with the crystal lattice structure in response to an external magnetic field, which is still poorly explored so far.…”

Terahertz dielectric properties of Fe3O4 thin films deposited on Si (100) substrate

“…At first the complex optical conductivity of reference substrate is measured For this, the Si substrate was placed in one of the slots of the sample holder (figure 2(a)) at the bottom of the VTI of the cryostat and the other slot was kept empty. At each temperature, the electric field amplitudes of THz beam passed through a 10 mm empty circular window (wos) and the reference substrate (ws) was measured [24,25]. In the second experiment, the electric field amplitudes of the THz beam passed through the reference substrate (ws) and the film on the substrate (wf ) was measured at the same temperatures where the optical properties of the substrate were measured earlier [24,25].…”

“…At each temperature, the electric field amplitudes of THz beam passed through a 10 mm empty circular window (wos) and the reference substrate (ws) was measured [24,25]. In the second experiment, the electric field amplitudes of the THz beam passed through the reference substrate (ws) and the film on the substrate (wf ) was measured at the same temperatures where the optical properties of the substrate were measured earlier [24,25]. The wos & ws and ws & wf were placed one after the other on the THz beam path using a stepper motor attached to the insert.…”