Comparative study of the Raman vibrational modes in pure and Fe-doped La2/3Ca1/3MnO3 thin films

Abstract

A comparative study of Raman spectra at room temperature of La2/3Ca1/3MnO3 (LCMO) and La2/3Ca1/3Mn0.97Fe0.03O3 (LCMFO) thin films, grown on monocrystalline substrates LaAlO3, is presented. The films were grown with thickness between 30 and 130 nm under identical deposition conditions by DC magnetron sputtering system at high O2 pressure. In order to observe changes in the vibration modes of the lattice due to the substitution of Mn by Fe ions, we compared the different values of wave numbers obtained from the fittings of each Raman spectrum. The results show that the characteristic–and most intense-peak at ∼486 cm−1 corresponds to the substrate. In the LCMO thick films, Raman modes are very weak and mix up with the substrate one, whereas in LCMFO, these modes were found in three intervals around 220–250 cm−1 (υ1), 450–520 cm−1 (υ2) and 610–720 cm−1 (υ3). A mode at ∼717 cm−1 is associated to structural disorder due to Fe doping effect. In both LCMO and LCMFO films, the conduction mechanism are related with electron localization and the electronic transition is mediated by phonons. According to the T* values from resistivity data fit (Variable Range Model -VRH), it is observed once more that the Fe doping relaxes the strain effects.