Comparative study on the roles of anisotropic epitaxial strain and chemical doping in inducing the antiferromagnetic insulator phase in manganite films

Epitaxial strain and chemical doping are two different methods that are commonly used to tune the physical properties of epitaxial perovskite oxide films, but their cooperative effects are less addressed. Here we try to tune the phase separation (PS) in (La1-xPrx)2/3Ca1/3MnO3 (0≤x≤0.4, LPCMO) films via cooperatively controlling the anisotropic epitaxial strain (AES) and the Pr doping. These films are grown simultaneously on NdGaO3(110),(LaAlO3)0.3(SrAl0.5Ta0.5O3)0.7(001), and NdGaO3(001) substrates with progressively increased in-plane AES, and probed by x-ray diffraction, magnetotransport, and magnetic force microscopy (MFM) measurements. Although it is known that for x=0 the AES can enhance the orthorhombicity of the films yielding a phase diagram with the antiferromagnetic charge-ordered insulator (AF-COI) state induced, which is quite different from the bulk one, we illustrate that the Pr doping can further drive the films towards a more robust COI state. This cooperative effect is reflected by the increasing magnetic fields needed to melt the COI phase as a function of AES and the doping level. More strikingly, by directly imaging the phase competition morphology of the LPCMO/NdGaO3(001) films via MFM, we find that during COI melting the PS domain structure is subject to both AES and the quenched disorder. However, in the reverse process, as the magnetic field is decreased, the COI phase reappears and the AES dominates leaving a crystalline-orientation determined self-organized microstructure. This finding suggests that the PS states and the domain configurations can be selectively controlled by the AES and/or the quenched disorder, which may shed some light on the engineering of PS domains for device fabrications.