Double Perovskites Nd₂CoMnO₆ Ceramics And La₂NiMnO₆ Films

Double perovskite ceramics have attracted much attention because of the excellentphysical properties, especially the magnetic properties. For the better understanding ofthe nature of electric and magnetic properties, Nd₂CoMnO₆ ceramics wereinvestigated to determine the physical nature of dielectric relaxations, the dielectricand magnetic characteristics. Meanwhile, La₂NiMnO₆ double perovskite films wereprepared by Pulsed Laser Deposition on Pt/TiCVSiCVSi substrate under differentdeposition conditions to pursue the best one.Dense Nd₂CoMnO₆ ceramics could be obtained by a solid state reaction process.A giant dielectric constant peak with strong frequency dispersion was observed, andthe corresponding dielectric relaxation was well fitted with the modified Debyeequation, and the parametersÏ„₀=3.41 ns and Ea=0.19 eV were obtained by theArrhenius fitting. The activation energy Ea is close to the energy required to transferan electron from Co²⁺ to Mn⁴⁺. Two ferromagnetic phase (FM) transitions weredetermined at the temperature of 150 K (T_c1) and 136 K (T_c2), respectively. Where,Tcl is the result of the interactions between Co²⁺-O-Mn⁴⁺, and T_c2 is related to theexistence of Co³⁺ resulting from an electron transfer from Co²⁺ to Mn⁴⁺.La₂NiMnO₆ thin films were prepared on Pt/TiO₂/SiO₂/Si substrates by the pulsedlaser deposition process. The temperature and the oxygen pressure played the primaryrole dominating the crystallization behavior and the morphology of La₂NiMnO₆ thinfilms. The well crystallized La₂NiMnO₆ thin films could be obtained at 873K and 923K under all oxygen pressures investigated here, and the fine morphology was obtainedunder the oxygen pressures equal to or higher than 50 Pa and 100 Pa, respectively.When the temperature was lower than 873 K or higher than 923 K, the wellcrystallized single phase La₂NiMnO₆ thin films could not be obtained. So pursuingthe best deposition condition is the most critical requirement for the high quality of thin film.