Spontaneous sharp metamagnetic transition in manganite films: influences of post-deposition annealing and measurement protocol

We report a detailed study of magnetic field-induced steplike metamagnetic transitions at 2K in phase separated Pr-0.65(CaySr1-y)(0.35)MnO3 (0.7 <= y <= 0.8) compounds, in the form of both polycrystalline pellets and films. Epitaxial films of Pr-0.65(CaySr1-y)(0.35)MnO3 PCSMO with thickness ranging from 100 to 7000 angstrom have been grown on (001) LaAlO3 (LAO) substrates using pulsed laser deposition (PLD) and their magnetic properties have been studied systematically. By comparing as-grown and annealed films, we find that the post-deposition annealing plays an important role in the synthesis and properties of manganite films. In particular, it releases strain and changes the microstructure, and we also argue that it changes the chemical homogeneity of the specimens. All of these factors impact the phenomenology of the sharp magnetization steps in PCSMO films. With a quick sweep of magnetic field, the magnetization steps occur only in thicker films (> 0.5 mu m) with y = 0.8. However, by modifying the measurement protocol, we demonstrate that the steps absent in other films can be recovered. We interpret this behavior to signify a dynamic self-organization of martensitic accommodation strain, consistent with the previously proposed martensitic-like scenario of the magnetization steps in bulk samples. (c) 2004 Elsevier B.V. All rights reserved.