No abstract

Although the magnetic phase diagrams of bulk and thin film samples of Pr 1−x Ca x MnO 3 (x ≤ 0.5) are widely explored, few works have been published on the magnetic properties of nanoparticles, especially in the lightly doped regime. In this paper, microwave irradiation was used to synthesize the Pr 0.977 Ca 0.023 MnO 3 and Pr 0.964 Ca 0.036 MnO 3 Manganite phases with Pnma space group in the form of anisotropic nanoparticles. The phase identification, structural characteristics, and formation of the nanostructures were analyzed by Rietveld analysis of the X-ray diffraction patterns, electron microscopy, and combining thermal analysis with infrared spectroscopy, respectively. Transport measurements on the annealed samples revealed the insulating nature, and electrical conduction occurs through thermally activated hopping of small polarons. The Mn−O c −Mn tilt angles in the MnO 6 octahedra show considerable flattening (160.9°and 167.6°for x = 0.023 and x = 0.036, respectively), possibly enhancing the electronic double exchange and promoting ferromagnetism. Ferromagnetic ordering of Mn spins was indeed observed below 109 K, and interestingly, the magnetic moment for x = 0.036 was 3.92 μ B /f.u. at 5 K, which is higher than the saturated Mn magnetic moment (3.8 μ B ). The enhanced magnetization is attributed to ordering of the Pr spins.

Separating out effects of point defects and lattice strain on thermal conductivity is essential for improvement of thermoelectric properties of SrTiO3. We study relations between defects generated during deposition, induced lattice strain, and their impact on thermal conductivity κ in homoepitaxial SrTiO3 films prepared by ion-beam sputtering. Lowering the deposition temperature gives rise to lattice expansion by enhancement of point defect density which increases the hardness of the films. Due to a fully coherent substrate-film interface, the lattice misfit induces a large biaxial strain. However, we can show that the temperature dependence of κ is mainly sensitive on the defect concentration.

Abstract

No abstract