Eur. Phys. J. B 37, 339-344 (2004)
https://doi.org/10.1140/epjb/e2004-00064-6

Study of infrared phonons in the La_0.7Sr_0.3MnO₃ manganite by means of reflectance measurements on epitaxial films

¹ COHERENTIA-INFM and Dipartimento di Fisica, Universitá di Roma “La Sapienza”, P.le A. Moro 5, 00185 Roma, Italy
² COHERENTIA-INFM and Dipartimento di Ingegneria Meccanica, Università di Roma Tor Vergata, Via del Politecnico 1, 00133 Roma, Italy

Corresponding author: ^a Paolo.Dore@roma1.infn.it

Received: 10 October 2003
Revised: 7 January 2004
Published online: 2 April 2004

Abstract

The optical phonon spectrum of the La_0.7Sr_0.3MnO₃ pseudocubic manganite has been investigated by means of far infrared reflectance measurements on high-quality films of different thickness grown by Pulsed Laser Deposition on LaAlO₃ and SrTiO₃ substrates. The manganite phonon spectrum, as obtained by properly modelling the measured reflectances, does not strongly depend on substrate and film thickness d. Measurements on thick-films (100<d<200 nm) on SrTiO₃ allow to precisely determine line profile and peak-frequency of bending ( cm and stretching (3 cm phonons of the bulk manganite. The bending phonon is broadened by an extra component around 365 cm^-1, which strongly decreases in intensity on decreasing d below 100 nm. Although this finding is not yet fully understood, the unambiguous conclusion is that thick-films on SrTiO₃ are ideal samples to get detailed information on the phonon spectrum of a bulk manganite.