Effect of large compressive strain on low field electrical transport in La0.88Sr0.12MnO₃thin films

We have investigated the effect of large in-plane compressive strain on the electrical transport in La 0.88 Sr 0.12 MnO 3 in thin films. For achieving large compressive strain, films have been deposited on single crystal LaAlO 3 (LAO, a = 3.798 Å) substrate from a polycrystalline bulk target having average in-plane lattice parameter a av = ( a b + b b )/2 = 3.925 Å. The compressive strain was further relaxed by varying the film thickness in the range ∼6–75 nm. In the film having least thickness (∼6 nm) large increase ( c = 3.929 Å) in the out-of-plane lattice parameter is observed which gradually decreases towards the bulk value ( c bulk = 3.87 Å) for ∼75 nm thick film. This shows that the film having the least thickness is under large compressive strain, which partially relaxes with increasing film thickness. The T IM of the bulk target ∼145 K goes up to ∼235 K for the ∼6 nm thin film and even for partially strain relaxed ∼75 nm thick film T IM is as high as ∼200 K. This enhancement in T IM is explained in terms of suppression of Jahn–Teller distortion of the MnO 6 octahedra by the large in-plane compressive strain. We observe a large enhancement in the low field magnetoresistance (MR) just below T IM in the films having partial strain relaxation. Thick films of 6 and 20 nm have MR ∼14% at 3 kOe that almost doubles in 35 nm film to ∼27%. Similar enhancement is also obtained in the case of the temperature coefficient of resistivity. The near doubling of low field MR is explained in terms of delocalization of weakly localized carriers around T IM by small magnetic fields.