Creating Ferromagnetic Insulating La0.9Ba0.1MnO3 Thin Films by Tuning Lateral Coherence Length.

Chao Yun,Judith L Macmanus-Driscoll,Yuxuan Peng,Haiyan Wang,Rui Wu,Jinbo Yang,Hongyi Dou,Xing Sun,Tuhin Maity,Xingyao Gao,Weiwei Li

doi:10.1021/acsami.1c00607

Abstract

In this work, heteroepitaxial vertically aligned nanocomposite (VAN) La0.9Ba0.1MnO3 (LBMO)-CeO2 films are engineered to produce ferromagnetic insulating (FMI) films. From combined X-ray photoelectron spectroscopy, X-ray diffraction, and electron microscopy, the elimination of the insulator–metal (I–M) transition is shown to result from the creation of very small lateral coherence lengths (with the corresponding lateral size ∼ 3 nm (∼7 u.c.)) in the LBMO matrix, achieved by engineering a high density of CeO2 nanocolumns in the matrix. The small lateral coherence length leads to a shift in the valence band maximum and reduction of the double exchange (DE) coupling. There is no “dead layer” effect at the smallest achieved lateral coherence length of ∼3 nm. The FMI behavior obtained by lateral dimensional tuning is independent of substrate interactions, thus intrinsic to the film itself and hence not related to film thickness. The unique properties of VAN films give the possibility for multilayer spintronic devices that can be made without interface degradation effects between the layers.

Highlights

Aligned nanocomposite (VAN) thin films have attracted significant attention[1,2] due to their ability to threedimensionally (3D) strain tune the physical properties of numerous functional systems, leading to improved ferroelectric, ferromagnetic, superconducting, and other functional properties.[3−6] the electronic properties of vertical interfaces can be controlled to have either higher or lower conduction, depending on the materials used.[7−10]It is widely known that film thickness is critical to the physical properties in standard epitaxial films of strongly correlated perovskite oxides
We showed that vertically aligned nanocomposite (VAN) LBMO films can be made much less conductive than plain films through changing film thickness.[39]
We show that when L is reduced, the films switch from being ferromagnetic metallic (FMM) to ferromagnetic insulating (FMI) at L

Summary

Introduction

Aligned nanocomposite (VAN) thin films have attracted significant attention[1,2] due to their ability to threedimensionally (3D) strain tune the physical properties of numerous functional systems, leading to improved ferroelectric, ferromagnetic, superconducting, and other functional properties.[3−6] the electronic properties of vertical interfaces can be controlled to have either higher or lower conduction, depending on the materials used.[7−10]It is widely known that film thickness is critical to the physical properties in standard epitaxial films of strongly correlated perovskite oxides. “emergent” properties can be induced that are drastically different from either bulk or thick plain films and beyond the interfacial region, other “dead layer” effects come into play.[12−15] The critical thickness below which the physical properties undergo drastic change is termed the “dimensional crossover”[16] thickness. It can be termed a vertical coherence length. In this low-thickness regime, in addition to modification of degrees of freedom from substrate interactions, strain-relieving defects from substrate−film lattice mismatch come into play, which complicate the understanding of low-dimensional effects.[17−20]

Methods

Results

Conclusion