  Magnetic and magnetotransport properties of oriented polycrystalline
Pr0.58Ca0.42MnO3 thin films prepared in flowing oxygen and air ambient has been
investigated. The magnetic ground state of both the films is a frozen cluster
glass. 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 hysteretic
insulator-metal transition (IMT) at TIMC=89 K and TIMW=148 K in the cooling and
warming cycle, respectively. Application of magnetic field (H) gradually
enhances TIMC and TIMW, reduces the thermoresistive hysteresis and TIM
diminishes. In contrast, the film annealed in flowing oxygen shows a CO
transition, which is followed by FM and AFM transitions. This film shows
appreciably smaller magnetic moment and does not show IMT upto H=20 kOe. As H
is increased to H=30 kOe, IMT having strong thermoresistive hysteresis and
sharp resistivity jumps appears in the cooling and warming cycles. As H
increases to higher values the thermoresistive hysteresis is reduced,
resistivity jumps are observed to disappear and TIM decreases. In the lower
temperature regime the resistivity first decreases slowly with H and then shows
sharp drop. The virgin cycle is not recoverable in subsequent cycles. The
decrement far more pronounced in the oxygen annealed film and occurs at much
higher H suggesting that the frozen cluster glass state is more robust in this
film. The microstructural analysis of the two set of films shows CO quenching,
FM transition and self-field IMT in air annealed film is caused by higher
density of microstructural disorder and lattice defects. The difference in
growth ambience of the two films could give rise to such microstructural
perturbations.
