Raman spectra in epitaxial thin films $La_{1-x}Ca_xMnO_3$ (x = 0.33, 0.5) grown on different substrates

TL;DR

This study investigates how temperature, doping, and substrate-induced strain influence the Raman spectra of La-Ca-Mn-O thin films, revealing strain-related modes and disorder effects linked to magnetic and charge-ordering transitions.

Contribution

It provides detailed analysis of strain and temperature effects on Raman spectra in epitaxial La-Ca-Mn-O films, highlighting strain-induced modes and their relation to physical properties.

Findings

Strain significantly alters Raman spectra in thin films.

A mode near 690 cm^{-1} is strain-dependent.

Disorder-related oxygen defect modes are observed under tensile strain.

Abstract

Raman spectra of LCMO films grown on LAO (001), STO (001), and MgO (001) substrates were studied at different temperatures. The effect of temperature, doping level and strain on Raman spectra are discussed in detail. With decreasing temperature, the changes of Raman spectra are correlated with the disorder-order transition, shuch as: paramagnetism to ferromagnetism, and charge-ordering. The strain induced by lattice-substrate mismatch affects the Raman spectra strongly. The mode induced by disorder of oxygen defects is apparently observed in $La_{0.67}Ca_{0.33}MnO_3$ film on STO due to the larger tensile strain. While this mode can not be seen in the Raman spectra for the films on LAO and MgO. A strong unsigned mode at about 690 $cm^{-1}$ is observed in all films except for $La_{0.67}Ca_{0.33}MnO_3$ film on LAO, which is not observed in bulk sample easily. It suggests that the mode is closely related to the strain.