Grain size-induced structural, magnetic and magnetoresistance properties of Nd_0.67Ca_0.33MnO₃ nanocrystalline thin films

The effects of grain size (G _S) on the structural, magnetic and magnetoresistance properties of sol–gel-derived Nd_0.67Ca_0.33MnO₃ (NCMO) nanocrystalline thin films were investigated. To change the G _S of the NCMO samples, the annealing temperature (T _A) was changed from 600 to 800 °C. All the prepared samples were confirmed as hexagonal single-phased polycrystalline structure. The average nanocrystalline size and G _S were increased with increasing T _A. The range of the G _S was approximately 25–40, 50–65 and 75–90 nm for the NCMO samples annealed at T _A = 600, 700 and 800 °C, respectively. As the G _S increased, the metal–insulator transition temperature, T _MI, and the paramagnetic–ferromagnetic transition temperature, T _C, also increased including the ferromagnetic response. The magnetoresistance, MR, values were found to increase with increasing the G _S at any annealing temperature.