Ferromagnetism, insulator-metal transition and magnetotransport in Pr0.58Ca0.42MnO3 films: role of microstructural perturbations

Abstract

Magnetic and magnetotransport properties of oriented polycrystalline Pr0.58Ca0.42MnO3 thin films prepared in flowing oxygen (O2) and air ambient have been investigated. In the air, annealed film charge order (CO) is quenched and ferromagnetic (FM) transition, which appears at TC ≈ 148 K is followed by antiferromagnetic (AFM) transition at TN ≈ 104 K. This film shows self-field insulator-metal transition (IMT) at ≈ 89 K and ≈ 148 K in the cooling and warming cycle, respectively. Magnetic field (H) enhances and , reduces the thermo-resistive hysteresis. The film annealed in O2 shows a CO transition at TCO ≈ 236 K, which is followed by FM and AFM transitions at TC ≈ 158 K and TN ≈ 140 K, respectively. No self-field IMT is observed in this film up to H = 20 kOe. At H ≥ 30 kOe, IMT having sharp resistivity jumps appears at ≈ 66 K and ≈ 144 K in the cooling and warming cycle, respectively. As H increases the resistivity jumps disappear and ΔTIM decreases. In the lower temperature regime (T = 5 K and 40 K) the H dependent resistivity (ρ-H) measurements show that the frozen cluster state is more robust in the O2 annealed film. At temperatures around TC, the ρ-H hysteresis and H induced drop in resistivity are more prominent in the O2 annealed film. At TC < T < TCO, higher H is required to induce IMT in the O2 annealed film. The magnetic and magnetotransport data clearly show that the film annealed in O2 has higher fraction of the AFM/COI phase, while the air annealed film has higher fraction of FMM phase. The microstructural analysis of the two set of films employing high resolution transmission electron microscopy reveals that the air annealed film has higher density of microstructural disorder and lattice defects, which could be responsible for CO quenching, FM transition and self-field IMT.