Eur. Phys. J. B 48, 255-258 (2005)
https://doi.org/10.1140/epjb/e2005-00401-3

Raman measurements on thin films of the La_0.7Sr_0.3MnO₃ manganite: a probe of substrate-induced effects

¹ Coherentia CNR-INFM and Dipartimento di Fisica, Università “La Sapienza”, P.le A. Moro 4, 00187 Roma, Italy
² Coherentia CNR-INFM and Dipartimento di Ingegneria Meccanica, Universita' di Roma Tor Vergata, via del Politecnico 1, 00133 Roma, Italy

Corresponding author: ^a paolo.dore@roma1.infn.it

Received: 27 July 2005
Published online: 16 December 2005

Abstract

We report on a Raman study of the phonon spectrum of La _0.7Sr_0.3MnO₃ thin films epitaxially grown on LaAlO₃. The spectrum, as a function of film thickness d, does not change over the 1000–100 Å range, whereas a strong hardening of the phonon frequencies of both bending and stretching modes is apparent in ultra-thin films (d<100 Å) where substrate-induced effects are remarkable. This behaviour, which appears to be related with the measured d-dependence of the insulator-to-metal transition temperature, is ascribed to co-operative effects of MnO₆ octahedra rotation and charge-localization. Raman spectroscopy proves to be a simple and powerful tool to monitor subtle structural modifications hardly detectable with conventional diffraction techniques in ultra-thin films.