n this work, a colossal magnetoresistive (CMR) Pr1−xCaxMnO3 (PCMO) man- 

ganite thin films and polycrystalline samples were studied with the main focus on the 

properties of the insulator to metal Mott phase transition. The polycrystalline PCMO 

samples were fabricated with the solid state reaction method. The polycrystalline sam- 

ples were further processed into the epitaxial thin films with the pulsed laser deposition 

method (PLD). The structural and magnetic properties of the samples were systemat- 

ically investigated and the thin films samples were further investigated with magneto- 

transport measurement where the thin films response to illumination was also studied. 

After the successful synthesis of polycrystalline PCMO samples with varying x = 

between 0.0 - 0.5, the magnetic characterization of the samples showed rich magnetic 

properties having the signatures of the magnetic phase coexistence of antiferromag- 

netic (AFM) and ferromagnetic (FM) ordering and cluster glass behaviour. With the 

increased doping concentration from x = 0.3 to 0.5, the AFM charge-order (CO) phase 

started to form up being strongest on the sample x = 0.5. This AFM CO phase could 

be melted with the high external magnetic field at temperatures below Neel’s tempera- 

ture TN inducing an irreversible first order metamagnetic AFM to FM phase transition. 

The strength of the AFM CO phase decreased with decreasing Ca concentration and 

increasing temperature. 

The polycrystalline PCMO samples with Ca concentrations of 0.3 - 0.5, showing 

metamagnetic behaviour, were selected for the fabrication of the thin film samples. The 

films were grown using two different in situ oxygen treatment temperatures at 500 ◦C 

and 700 ◦C in the PLD system. The films with x = 0.4 and 0.5 showed weaker AFM CO 

phase with greatly reduced melting fields when compared to polycrystalline samples. 

Also, the robustness of the AFM CO phase was further decreased in thin films with the 

lower oxygen treatment temperature of 500 ◦C. The magneto-transport measurements 

made on the thin films showed that the melting of AFM CO phase was connected to 

CMR effect where the increasing magnetic field induced an insulator to metal phase 

transition, which reduces the resistivity of the film around nine orders of magnitude. 

The use of illumination during the magneto-transport measurements showed a vari- 

ety of intriguing phenomena including magnetophotoresistance. The illumination had 

a huge effect to the insulator to metal transition (IMT) reducing the transition magnetic 

field significantly. Moreover, by magnetically biasing the thin films with the constant 

external magnetic field, the IMT could be induced by switching on the illumination.