Single-domain to Multi-domain Transition Due to Phase Separation in (La_1-yPr_y)_1-xCa_xMnO₃ Thin Films

The perovskite manganite (La_1-yPr_y)_1-xCa_xMnO₃ exhibits complex electronic and magnetic behaviors caused by a phase competition between its ferromagnetic metallic (FMM) and charged order insulating (COI) phases. While La_0.67Ca_0.33MnO₃ (x = 0.33, y = 0) undergoes a transition from a paramagnetic insulator to a pure FMM below 250 K, (La_0.4Pr_0.6)_0.67Ca_0.33MnO₃ (x = 0.33, y = 0.6) shows electronic phase-separation between FMM and COI phases at temperatures approximately below 120 K. Thin films of (La_1-yPr_y)_1-xCa_xMnO₃ (x = 0.33, y = 0, 0.5, 0.6) were grown on (110) NdGaO₃ (NGO) using pulsed laser deposition. Among these thin films, (La_0.4Pr_0.6)_0.67Ca_0.33MnO₃ also shows a single-domain to multi-domain transition in the FMM regions as they percolate at low temperatures. This domain transition is partially due to the in-plane uniaxial magnetic anisotropy caused by the anisotropic substrate strain exerted by (110) NGO. To check if phase separation also plays a role in the domain transition, we measured the temperature dependence of the coercive field (H_c) for y = 0 and y = 0.5 thin films. These films show a monotonic increase in H_c with lowering temperature showing that phase separation and a percolation of the FMM regions is required for the domain transition.