Strain effect on the magnetic and transport properties of LaCoO3 thin films

Y Li,D J Wang,S H Wang,S J Peng,K M Wu

doi:10.1063/1.5006280

Abstract

LaCoO3 (LCO) has attracted much attention due to the unique magnetic transition and spin transition of Co3+ ions. Epitaxial LCO film exhibits an unexpected ferromagnetism, in contrast to the non-magnetism of bulk LCO. An in-depth study on the property of strained LCO film is of great importance. We have fabricated 30 nm LCO films on various substrates and studied the magnetic and transport properties of films in different strain states (compressed strain for LCO/LaAlO3, tensile strain for LCO/(LaAlO3)0.3(Sr2TaAlO6)0.35, SrTiO3). The in-plane tensiled LCO films exhibit ferromagnetic ground state at 5K and magnetic transition with TC around 85K, while compressed LCO/LaAlO3 film has a negligibly small moment signal. Our results reveal that in-plane tensile strain and tetragonal distortion are much more favorable for stabilizing the FM order in LCO films.

Highlights

The lanthanum cobaltate LaCoO3 (LCO) is a perovskite complex oxide material, which has been studied extensively both theoretically and experimentally in the past few years, due to its unique magnetic transition and spin transition of Co3+ ions from diamagnetic low spin (LS, S=0) state, to paramagnetic high spin (HS, S=2) state, as the temperature increases above ∼ 80K.1 The ground state of bulk LCO is non-magnetic with Co3+ ions in the LS state at low temperature
An unexpected ferromagnetic (FM) order has been observed in epitaxial LCO films which are subjected to in-plane tensile strain, e.g., LCO films grown on SrTiO3 (STO) and (LaAlO3)0.3(Sr2TaAlO6)0.35 (LSAT).[4,5,6,7,8,9,10]
Our results demonstrate that in-plane tensile strain and tetragonal distortion are much more favorable for stabilizing the FM order in LCO films

Summary

Introduction

The lanthanum cobaltate LaCoO3 (LCO) is a perovskite complex oxide material, which has been studied extensively both theoretically and experimentally in the past few years, due to its unique magnetic transition and spin transition of Co3+ ions from diamagnetic low spin (LS, S=0) state, to paramagnetic high spin (HS, S=2) state, as the temperature increases above ∼ 80K.1 The ground state of bulk LCO is non-magnetic with Co3+ ions in the LS state at low temperature. The ground state of bulk LCO is non-magnetic with Co3+ ions in the LS state at low temperature. Relatively weak dynamic ferromagnetic and antiferromagnetic properties were reported in bulk LCO.[2,3] an unexpected ferromagnetic (FM) order has been observed in epitaxial LCO films which are subjected to in-plane tensile strain, e.g., LCO films grown on SrTiO3 (STO) and (LaAlO3)0.3(Sr2TaAlO6)0.35 (LSAT).[4,5,6,7,8,9,10] This finding has attracted scientists’ attention rapidly and a lot of research work has been done on the novel magnetic property and spin state in LCO film since . The magnetism in compressive film is controversial, e.g., some researchers have observed FM order in compressed LaAlO3 (LAO) film,[4,11] but some haven’t.12 More surprising, almost all first-principles calculations predicted that the half metallicity would evolve along with the FM state in LCO thin film,[13,14] but people only observed FM insulating behavior until now.[11,15]

Methods

Results

Conclusion