Controlling the sharpness of metal-insulator transition in epitaxial (La1−xPrx)0.67Ca0.33MnO3 (0 ≤ x ≤ 0.35) films

Abstract

We report that epitaxial strain and chemical doping can be used cooperatively to tune the sharpness of metal-insulator transition (MIT) in epitaxial (La1−xPrx)0.67Ca0.33MnO3 (LPCMO) films. Compared to multiple MITs in anisotropically strained LPCMO/(LaAlO3)0.3(SrAl0.5Ta0.5O3)0.7(001)C (LSAT) films with a phase-separated ground state, the lattice-matched LPCMO/NdGaO3(110)Or (NGO) films show a sharp MIT near the Curie temperature (TC), with a ferromagnetic-metallic ground state. The sharpness of MIT, as evaluated by the temperature coefficient of resistance (TCR), can be two times larger in LPCMO/NGO films than in LPCMO/LSAT films. Moreover, for LPCMO/NGO films, TCR greatly relies on the Pr doping level x, where a maximum TCR value of 88.17% K−1 can be obtained at x = 0.25, but shows less dependence on the film thicknesses. These results suggest that the combination of epitaxial strain and chemical doping could be employed to control not only the ground state of the manganite films, but the sharpness of MIT at various TC, providing the feasibility to design manganite-based infrared devices in a broad temperature range.