A-site Ordering versus Electronic Inhomogeneity in CMR-Manganite Films

TL;DR

This study investigates how A-site cation ordering in LaCaMnO3 thin films influences their structural and electronic properties, revealing that ordered films exhibit sharp phase transitions and electronic homogeneity, challenging the typical phase separation model for colossal magnetoresistance.

Contribution

It demonstrates that A-site cation ordering enhances electronic homogeneity and sharp phase transitions in CMR manganite films, providing new insights into the mechanisms behind colossal magnetoresistance.

Findings

Ordered films show sharp insulator-metal and magnetic transitions.

Ordered films are electronically homogeneous down to 1 nm scale.

Large CMR observed even without phase separation.

Abstract

Epitaxial La3/4Ca1/4MnO3/MgO(100) (LCMO) thin films show unusual rhombohedral (R-3c) structure with a new perovskite superstructure due to unique ordering of La and Ca at the A-site positions. Very sharp insulator-metal and para-ferromagnetic phase transitions at temperatures up to TMI ~ TC=295 K were observed. The ordered films were electronically homogeneous down to 1 nm scale as revealed by scanning tunnelling microscopy/spectroscopy. In contrast, orthorhombic and A-site disordered LCMO demonstrate broadened phase transitions as well as mesoscopic phase separation for T<<TC. The unique La/Ca ordering suppresses cation mismatch stress within one super-cell, a~1.55 nm, enhancing electronic homogeneity. Phase separation scenario seems not to be a unique mechanism for CMR as very large CMR=500 % was also observed in A-site ordered films.