Annealing assisted substrate coherency and high-temperature antiferromagnetic insulating transition in epitaxial La0.67Ca0.33MnO3/NdGaO3(001) films

L F Wang,X L Tan,B B Chen,W B Wu,P F Chen,B W Zhi,G Y Gao,Z Huang

doi:10.1063/1.4804541

Abstract

Bulk La0.67Ca0.33MnO3 (LCMO) and NdGaO3 (NGO) have the same Pbnm symmetry but different orthorhombic lattice distortions, yielding an anisotropic strain state in the LCMO epitaxial film grown on the NGO(001) substrate. The films are optimally doped in a ferromagnetic-metal ground state, after being ex-situ annealed in oxygen atmosphere, however, they show strikingly an antiferromagnetic-insulating (AFI) transition near 250 K, leading to a phase separation state with tunable phase instability at the temperatures below. To explain this drastic strain effect, the films with various thicknesses were ex-situ annealed under various annealing parameters. We demonstrate that the ex-situ annealing can surprisingly improve the epitaxial quality, resulting in the films with true substrate coherency and the AFI ground state. And the close linkage between the film morphology and electronic phase evolution implies that the strain-mediated octahedral deformation and rotation could be assisted by ex-situ annealing, and moreover, play a key role in controlling the properties of oxide heterostructures.

Highlights

For the past decades, researches in transition-metal perovskite oxides have flourished
To explain this drastic strain effect, the films with various thicknesses were ex-situ annealed under various annealing parameters
We develop a new strategy by investigating the surface morphology and magnetotransport property in parallel from the LCMO/NGO(001) films with various thicknesses after being ex-situ annealed under various annealing parameters

Summary

INTRODUCTION

Researches in transition-metal perovskite oxides have flourished. Based on observed close relationship between the epitaxial quality and phase evolution, along with the quantitative analyses of the octahedral response to the anisotropic strain, we suggest that after annealing the enhanced substrate coherency could stabilize the Jahn-Teller distortion in the LCMO films and trigger the AFI phase

EXPERIMENT

RESULTS AND DISCUSSION

CONCLUSIONS