Modelling of strain effects in manganite films

TL;DR

This paper models how strain and thickness influence the magnetic and transport properties of manganite films, aligning theoretical predictions with experimental observations by considering bond angle effects and electron-phonon interactions.

Contribution

It extends a variational approach to thin films, incorporating substrate-induced strain effects on electron hopping and phase coexistence in manganite films.

Findings

Thinner films show lower critical temperature and magnetization.

Strain modifies electron hopping amplitudes, affecting transition temperatures.

Properly accounting for bond angle dependence is crucial for accurate modeling.

Abstract

Thickness dependence and strain effects in films of $La_{1-x}A_xMnO_3$ perovskites are analyzed in the colossal magnetoresistance regime. The calculations are based on a generalization of a variational approach previously proposed for the study of manganite bulk. It is found that a reduction in the thickness of the film causes a decrease of critical temperature and magnetization, and an increase of resistivity at low temperatures. The strain is introduced through the modifications of in-plane and out-of-plane electron hopping amplitudes due to substrate-induced distortions of the film unit cell. The strain effects on the transition temperature and transport properties are in good agreement with experimental data only if the dependence of the hopping matrix elements on the $Mn-O-Mn$ bond angle is properly taken into account. Finally variations of the electron-phonon coupling linked to the presence of strain turn out important in influencing the balance of coexisting phases in the film