Phase-separated manganites: The effect of reversible elastic lattice strain on the electronic properties

In this work, the effect of reversible elastic lattice strain on the electronic properties of a) (Pr1−y Lay )0.7 Ca0.3 MnO3 (PLCMO) thin films and b) the interface layer of La0.7 Sr0.3 MnO3 (LSMO) with SrTiO3 (STO) has been determined using piezoelectric substrates. Lattice strain is known to effectively alter the electronic structure of compounds from the manganite family, since it shifts the balance of competing electronic interactions by changing bond angles and bond lengths.The PLCMO films have been repared by pulsed laser deposition (PLD) from a La0.7 Ca0.3 MnO3 (LCMO) and a Pr0.7 Ca0.3 MnO3 (PCMO) target. The metal- insulator phase boundary has been established to lie around y = 0.6. In films with y = 0.6, the piezoelectric release of tensile strain in the film plane induces a drastic reduction of the resistance, or a “colossal” elastoresistance. Resistive gauge factors as high as Γ = 1000 have been found. Consistent with the transport results, the release of tensile strain leads to an increase in both the Curie temperature and the magnetisation. The coexistence of the ferromagnetic metallic (FMM) and charge ordered insulating (COI) phases in PLCMO has been found to be strongly affected by the reversible substrate strain. Both the magnetisation and the resistance data in controlled strain states demonstrate a strong suppression of the ferromagnetic double exchange interaction by tensile strain. [La0.7 Sr0.3 MnO/SrTiO3 ] superlattices have been deposited on STO and piezoelectric PMN-PT (001) (PbMg1/3 Nb2/3 O3 )0.72 (PbTiO3 )0.28 substrates by PLD. X-ray reflectivity (XRR) measurements show clear Kiessig fringes as well as the larger interference maxima caused by the superlattice, giving qualitative proof of a well defined superlattice structure with sharp interfaces on both substrates. With decreasing LSMO layer thickness d, the samples show a sharp decrease of the Curie temperature, accompanied by a decrease of the saturation magnetisation and an increase of the coercive field around d = 5 nm. Reversible strain measurements on thicker superlattices (d = 16.7 nm) reveal a behaviour of the magnetisation similar to that of single thick films of LSMO. When d is decreased, the strain induced relative change in magnetisation ∆M/M0 shows a behaviour comparable to PLCMO thin films. This has been attributed to the increased volume fraction of the LSMO inter- face layer with STO, which displays a reduced magnetic order and phase-separated tendencies. From the absolute change in magnetisation per interface, the thickness of the so-called magnetically “dead” layer of the LSMO has been estimated to lie between 1.3 nm and 1.7 nm in the superlattices grown on PMN-PT