Strain induced phase transition in La${}_{0.2}$Sr${}_{0.8}$MnO${}_3$

We explore the structural and magnetic tunability of polycrystalline La${}_{0.2}$Sr${}_{0.8}$MnO${}_3$ sample by varying preparation conditions using solid state reaction method. Low temperature X-ray diffraction studies indicate that one of the samples shows a transition from cubic Pm-3m structure to dominant tetragonal I4/mcm structure below ∼260 K, while the other sample exhibits transformation from cubic structure to a dominant phase with fundamental reflections corresponding to P4/mmm tetragonal symmetry below ∼260 K, followed by an incomplete transition from this phase to tetragonal I4/mcm phase below ∼225 K. The Rietveld analysis at 260K indicates that the former sample exhibits co-existence of cubic Pm-3m, tetragonal I4/mcm and P4/mmm phases while the latter sample shows the co-existence of Pm-3m and tetragonal P4/mmm phases. Density functional theory(DFT+U) calculations suggest C-type antiferromagnetic and d${}_{3z^2-r^2}$ orbital ordering in I4/mcm structure and A-type antiferromagnetic with d${}_{x^2-y^2}$ orbital ordering in P4/mmm structure. The results show a possibility of tuning magnetic structure from C-type antiferromagnetic to A-type antiferromagnetic in an intermediate temperature range at fixed concentration, by varying the strain fields. At high temperatures (300-518 K), the resistivity follows small polaron hopping model in both the samples and change in preparation conditions leads to a change over from adibatic to non-adibatic limit. Above 518 K, both the samples exhibit metallic resistivity. Our results open a new avenue for tuning magnetic and structural phases in phase separated systems, and such tunability may be useful in antiferromagnetic spintronic, designing correlated electron-based electronic devices.