Thickness dependent Raman study of epitaxial LaMnO3 thin films

• A progressive release of strain with increasing film thickness was observed.
• Decrease in metal insulator and ferromagnetic transition temperature is observed.
• This decrease is related with Jahn–Teller (JT) distortion.
• JT distortion is found to increase with decreasing film thickness.
• Decrease in JT distortion results in lower transition temperature.

Epitaxial thin films of LaMnO3 of increasing thickness from 20 nm to 200 nm are deposited on LaAlO3 (001) substrates by pulsed laser deposition. The films are in-plane compressively strained and a 20 nm film is fully strained. The strain relaxation mechanism in these films is studied by X-ray diffraction and it is observed that the strain relaxes gradually as the thickness is increased. The low temperature Raman measurements on these films revealed that the Jahn–Teller distortion is responsible for the magnetic transition temperature in these films. The Jahn–Teller distortion is found to increase with decreasing film thickness that results in decreasing magnetic transition temperature. The films with thicknesses of 40 and 20 nm showed structural quenching due to strong strain imposed by the substrate.