Strain-Dependence of the Structure and Ferroic Properties of Epitaxial NiTiO3Thin Films Grown on Different Substrates

Tamas Varga,Mark E Bowden,Timothy C Droubay,Libor Kovarik,Dehong Hu,Scott A Chambers

doi:10.1155/2015/493045

Abstract

Polarization-induced weak ferromagnetism has been predicted a few years back in perovskite MTiO3(M = Fe, Mn, and Ni). We set out to stabilize this metastable perovskite structure by growing NiTiO3epitaxially on different substrates and to investigate the dependence of polar and magnetic properties on strain. Epitaxial NiTiO3films were deposited on Al2O3, Fe2O3, and LiNbO3substrates by pulsed laser deposition and characterized using several techniques. The effect of substrate choice on lattice strain, film structure, and physical properties was investigated. Our structural data from X-ray diffraction and electron microscopy shows that substrate-induced strain has a marked effect on the structure and crystalline quality of the films. Physical property measurements reveal a dependence of the weak ferromagnetism and lattice polarization on strain and highlight our ability to control the ferroic properties in NiTiO3thin films by the choice of substrate. Our results are also consistent with the theoretical prediction that the ferromagnetism in acentric NiTiO3is polarization induced. From the substrates studied here, the perovskite substrate LiNbO3proved to be the most promising one for strong multiferroism.

Highlights

There has been a recent wave of interest in the MTiO3 (M = Fe, Mn, and Ni) compounds as a result of a theoretical prediction that their polymorph crystallizing in space group R3c exhibits multiferroic properties and may enable switching of the direction of magnetization by the application of an electric field [1, 2]
Based on high-resolution X-ray diffraction (HRXRD) and transmission electron microscopy (TEM), we describe the effect of strain from lattice mismatch on the structure of the films
From our complimentary physical property characterization by DC magnetization and second harmonic generation (SHG), we infer that our NiTiO3/Al2O3 and NiTiO3/LiNbO3 films exhibit polarization-induced weak ferromagnetism and that the choice of substrate can be employed to control the ferroic properties of these potentially multiferroic films

Summary

Introduction

Al2O3 exerts a large compressive strain on NiTiO3, which may promote the stabilization of the metastable LNOtype structure, but the effect of smaller and/or tensile strains on LNO-type MTiO3 films is still unknown. Both compressive and tensile strains are known to promote multiferroic properties in the same compound [12]. From our complimentary physical property characterization by DC magnetization and second harmonic generation (SHG), we infer that our NiTiO3/Al2O3 and NiTiO3/LiNbO3 films exhibit polarization-induced weak ferromagnetism and that the choice of substrate can be employed to control the ferroic properties of these potentially multiferroic films

Experiment

Results and Discussion

Conclusions