Structure, electrical transport, and magnetoresistance of manganite films on sapphire

In this work, Pr_0.7Sr_0.3MnO₃ (PSMO) films with the thickness of 12 and 36 nm have been grown on (0001) sapphire substrates with six symmetry using pulsed laser deposition technology. The structure, electrical transport, and magnetoresistance (MR) of PSMO films have been investigated. In the PSMO film with the thickness of 12 nm, there is only one metal-to-insulator (MI) transition. Some textures and disorder coexist in the 12-nm-thick PSMO film, reducing temperature dependence of MR. This kind of MR can be explained by the double exchange (DE) theory. We find a low-field MR (LFMR) ~ 38% (at µ₀H  = 1 T, T = 80 K) and a MR ~ 125% (at µ₀H  = 5 T, T = 185 K) in this thinner PSMO (12 nm) film. On the contrary, there are two MI transitions in the PSMO film with the thickness of 36 nm. The LFMR ~ 55% (at µ₀H  = 1 T, T = 115 K) and MR ~ 300% (at µ₀H  = 5 T, T = 140 K) are obtained in this thicker PSMO (36 nm) film. This kind of MR cannot be explained by the DE theory, which is induced by the charge-ordered antiferromagnetic state. The electrical transport and the MR can be tuned by the charge ordering, multiple textures and the disordering induced by both grain boundary and large lattice mismatch between PSMO film and sapphire. These interesting physical properties in manganite films have opportunities for practical application in developing manganite-based magnetic sensor and memory devices.