Microstructural and magnetotransport properties of La1 − xCaxMnO3 (0.45 ≤ x ≤ 0.60) thin films

Abstract

In the present work we focus on the coexistence of magnetic-electronic phases and hence phase separation in La1−xCaxMnO3 thin films in the composition range of 0.45≤x≤0.60. The oriented polycrystalline thin films were prepared by nebulized spray pyrolysis technique on single crystalline substrate LaAlO3 [LAO (001)]. The lattice parameters are observed to decrease with increasing in Ca content and the structural/microstructural disorder is also seen to increase concomitantly. As the Ca content is increased from x=0.45 to 0.55, the paramagnetic insulator (PMI) to ferromagnetic metal (FMM) transition temperatures (TC/TIM) are suppressed. This is accompanied by (i) appreciable suppression of the TC, (ii) sharp reduction in the magnetic moment, (iii) occurrence of a peak in the magnetization below TC, (iv) stronger bifurcation of the ZFC–FC magnetization, and (v) decline in the magnetization in the lower temperature regime. At x=0.60, the FMM disappears and a weak FM insulator like phase is observed. In the vicinity of x=0.55, the magnetic ground state resembles spin cluster glass. This is also confirmed by the occurrence of a hysteresis loop in the resistivity of the x=0.55 measured during the cooling and warming cycle. The transition broadening up to x=0.55 and the vanishing of the two transitions in x=0.60 film along with the simultaneous decrease in the magnetic moment and enhanced resistivity show that the observed variations are due to the increase in the antiferromagnetic-charge ordered (AFM-CO) phase fraction at higher Ca content. This is also confirmed by the decrease in magnitude of the magnetoresistance and its temperature dependence. Our results demonstrate that, there is strong phase separation in the overdoped region (0.50<x≤0.60) due to the presence of multiple magneto-electric phases.