Growth and characterization of La1 − xAxMnO3 (A = Ag and K, x = 0.33) epitaxial and polycrystalline manganite thin films derived by sol-gel dip-coating technique

Manganite La_0.67Ag_0.33MnO₃ (LAgMO) and La_0.67K_0.33MnO₃ (LKMO) films have been obtained on a single-crystal of LaAlO₃ (100) and quartz substrates using sol-gel dip-coating technique. Structural, electrical, magnetic and magnetoresistance properties of the films have been investigated. X-ray diffraction patterns of the films grown on LaAlO₃ (100) substrate showed to be highly oriented in the direction of (100) and the films grown on the quartz substrate have perovskite with rhombohedral structure. The oriented films exhibited typical transport properties, whereas the polycrystalline films showed significantly different behaviors of the temperature dependent resistivity, magnetization and magnetoresistance (MR). The epitaxial films of the LAgMO and LKMO showed different metal-insulator transition temperature (T_MI) and the paramagnetic-ferromagnetic phase transition temperature (T_C). This was mainly due to the different ionic radius size of Ag¹⁺ and K¹⁺. The variation of T_MI and T_C was due to the different annealing temperatures and grain size effect in the polycrystalline films. The polycrystalline films showed a higher MR than the corresponding epitaxial films. An extrinsic MR has been observed at low temperatures (< 100 K) for the polycrystalline films due to the spin dependent scattering of conduction electrons at grain boundaries.