Columnar defect induced phase transformation in epitaxial La0.7Ca0.3MnO3 films

• Published in: Journal of applied physics 2000-05, Vol.87 (9), p.4210-4215
• Main Authors: Ogale, S. B., Li, Y. H., Rajeswari, M., Riba, L. Salamanca, Ramesh, R., Venkatesan, T., Millis, A. J., Kumar, Ravi, Mehta, G. K., Bathe, Ravi, Patil, S. I.
• Format: Article
• Language: English
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.373054

Epitaxial La0.7Ca0.3MnO3 thin films on the SrTiO3(100) surface have been irradiated with 250 MeV Ag17+ ions at different nominal fluence values in the range of 5×1010–4×1011 ions/cm2, resulting in columnar defects. At low fluences these defects cause changes in material properties that are small and scale linearly with dosage. Above a threshold fluence value ∼3×1011 ions/cm2 dramatic changes are observed, including an order of magnitude increase in the resistivity and 50 K drop in the Curie temperature. Transmission electron microscopy measurements show that the changes are associated with a phase transformation of the undamaged region between the columnar defects. The transformed phase has a diffraction pattern very similar to that seen in charge-ordered La0.5Ca0.5MnO3. We propose that above a critical level of ion damage, strains caused by the presence of the columnar defects induce a charge-ordering phase transition that causes the observed dramatic changes in physical properties. We speculate that a conceptually similar surface-induced charge ordering may be responsible for the “dead layer” observed in very thin strained films, and the dramatic changes in optical properties induced by polishing, and that an impurity-induced charge ordering causes the extreme sensitivity of properties to lattice substitution.