Double-strain effect in doped La_0.7Ca_0.3MnO₃ PLD grown thin films and fabrication of high-resistance tunnel junction using a novel nano-scale insulating tunnel barrier

Thin films of La_0.65R_0.05Ca_0.3MnO₃ (R = Ho and Y) grown using pulsed laser deposition (PLD) technique on (100) NdGaO₃ (NGO) single-crystal substrates have shown a decrease in T_P farther from the corresponding values obtained on bulk samples. This decrease could be attributed to an additional substrate strain effect. The uniqueness of the present result is that Ho-doped La_0.7Ca_0.3MnO₃ (LCMO) films have shown drastic reduction in resistance (ρ_max) compared to that of Y-doping similar to what has been observer in the bulk samples. We have also fabricated a novel FM/I/FM (FM = ferromagnet (La_2/3Ba_1/3MnO₃ (LBMO) in this case); 1 = insulator) tunnel junction by replacing the widely used SrTiO₃ (STO) insulating layer by an insulating phase of Ho-doped LCMO composition (La_0.55Ho_0.15Ca_0.3MnO₃) to study the MR and electronic correlation effects. High resistance values have been realized across junctions made up of the LCMO-based insulating layer. This result could open up new avenues in TMR research.