In the present study, we have synthesized polycrystalline samples of BaTi[Formula: see text]CoxO3 (BTCO) ([Formula: see text], 0.01, 0.03, 0.05, 0.07 and 0.10) with standard solid state reaction technique. The obtained samples are characterized by X-ray diffraction (XRD) and Raman spectroscopy for structural study. The detailed structural analysis has been performed by Rietveld refinement using Fullprof program. We observed an increase in lattice parameters, which results due to substitution of Co[Formula: see text] with large ionic radii (0.9[Formula: see text]Å) for smaller ionic radii (0.6[Formula: see text]Å) Ti[Formula: see text]. Moreover, peak at 45.5∘ shifts to 45∘ on Co doping, which is due to structure phase transition from tetragonal to cubic. Raman study infers that the intensity of characteristic peaks decreases and line width increases with Co doping. The bands linked with the tetragonal structure (305[Formula: see text]cm[Formula: see text]) decreased due to the tetragonal-to-cubic phase transition with Co doping. Our structural study reveals the expansion of BTCO unit cell and tetragonal-to-cubic phase transformation takes place. The results from different characterization techniques are conclusive and show structural evolution with Co doping. The samples are further characterized by dielectric spectroscopy, dielectric measurement reveals the increase of dielectric constant and transition [Formula: see text]C is observed for Barium titanate (BaTiO3), whereas transition disappears with Co doping. Both temperature and frequency-dependent tangent loss is also studied.

Double perovskite (DP) oxide material receive extensive research interest due to exciting physical properties with potential technological application. 3d based DP oxides are promising for exciting physics like magnetodielectric, ferroelectric, Griffith phase etc., specially Co/Mn DPs are gaining much research interest. In this paper we present the study of magnetic phase and transport properties in nano-crystalline Pr2CoMnO6 a 3d based double perovskite compound. This material shows a paramagnetic (PM) to ferromagnetic (FM) phase transition below 173 K marked by a rapid increase in magnetic moment due to spin ordering. We found divergence in inverse magnetic susceptibility (χ −1 ) from Curie weiss behavior around 206 K which indicates the evolution of Griffiths phase before actual PM-FM transition. We found that the Griffiths phase suppressed with increasing applied magnetic filed. For the understanding of charge transport in this material we have measured temperature dependent electrical resistivity. Pr2CoMnO6 is a strong insulator where resistivity increase abruptly below magnetic phase transition. To understand the effect of magnetic field on transport behavior we have also measured the magnetoresistance (MR) at different temperatures. Sample shows the negative MR with maximum value ∼22 % under applied magnetic field of 50 kOe at 125 K. MR follows quadratic field dependency above Tc however below Tc the MR shows deviation from this field dependency at low field.

To understand the nature of magnetic phase transition in nano-crystalline Pr2CoMnO6, in present study we have investigated the critical behavior and magnetocaloric effect. To estimate the critical exponents, various methods have been adopted like; the modified Arrott plots (MAP), the Kouvel-Fisher method (KF) and the critical isotherm analysis. This material shows a second order type a paramagnetic (PM) to ferromagnetic (FM) phase transition around 160 K. The critical exponents obtained from modified Arrott plots are β = 0.531, γ = 0.935 and Tc = 160 K. Kouvel-Fisher method gives the exponents as β = 0.533±0.001 with Tc = 160.72±0.03 K and γ = 0.932±0.003 with Tc = 160.15±0.05 K. The third exponent δ = 2.763±0.005 obtained from critical isothermal is in agreement with Wisdom scaling rule. The estimated critical exponents do not exactly match with any established universality class, however, the deduced exponent values suggest that spin interaction in the present material is close to mean-field model which suggests the existence of longrange ferromagnetic order in nano-crystalline Pr2CoMnO6. The reliability of critical exponents is checked by universal scaling hypothesis on magnetic data across Tc. We have calculated the magnetic entropy change from magnetic data and found maximum value of -∆S = 2.05 (J kg −1 K −1 ) for 50 kOe at 180 K. Moreover, field dependent change in magnetic entropy obeys scaling and also indicates that the magnetic interaction is close to mean-field type.

3d based double perovskite materials have received much attention in recent years due to their exotic magnetic structure and magneto-electric coupling. In this work we have prepared and studied the nano-crystalline sample of Ho 2 CoMnO 6 . Structural, magnetic, Raman and dielectric properties have been studied in detail. The structural analysis shows that the sample crystallize in monoclanic crystal structure with P2 1 /n phase group. The X-ray photoelectron spectroscopy have been employed to confirms the charge state of cations presents in the material. Magnetic study shows that the sample undergoes a paramagnetic to ferromagnetic phase transition around T c ∼85 K. The isothermal magnetization measurements shows hysteresis curve hence confirm ferromagnetic behavior at low temperature. Temperature dependent Raman study reveals that there is spin phonon coupling in the sample marked by deviation in phonon mode from anharmonic behavior. Dielectric response of Ho 2 CoMnO 6 shows the large dispersion and large dielectric constant. Impedance spectroscopy and electrical modulus study reveal that system shows deviation from ideal Debye model. AC conductivity have been studied as a function of both temperature and frequency. We found that the conduction mechanism is obeyed by Jonscher's model. The exponent factor n is suggest that the material deviates from ideal Debye model.

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In this paper, we present the spin-phonon coupling and dielectric response of nano-crystalline Pr 2 CoMnO 6 employing Raman and dielectric spectroscopic study. Pr 2 CoMnO 6 is a manganite compound , it undergoes a paramagnetic to ferromagnetic (PM-FM) phase transition around T c ∼172 K. Temperature-dependent Raman scattering experiment is carried out across T c to study the spin-phonon behavior in this material. The results from Raman study reveal an obvious softening of the phonon mode involving stretching vibrations of the (Co/Mn)O 6 octahedra in ferromagnetic temperature regions, indicating a close correlation between magnetism and lattice in Pr 2 CoMnO 6 and conform the spin phonon coupling. Further, we have carried out detailed study on dielectric response, impedance spectroscopy, electric modulus and AC conductivity of Pr 2 CoMnO 6 ceramics in the temperature range of 20 K -300 K and frequency range of 1kHz -5.5MHz. We found Pr 2 CoMnO 6 shows strong frequency dependence with large dispersion and large dielectric constant. It is found that thermally activated relaxation mechanism is involve and material is deviated from Debye's model which is confirmed by Nyquist plot and complex modules behavior.

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