The role of epitaxial strain on the electronic and magnetic structure of La0.7Sr0.3MnO3/LaCoO3 bilayers

S Das,S Thota,R Medwal,R G Tanguturi,R S Rawat,S Gupta,S Das,S Ghosh,R K Dokala

doi:10.1063/5.0071572

Abstract

Realizing atomically flat interfaces between the ultrathin perovskite oxides is a challenging task, which usually possess different chemical environments, depending on the terminating lattice planes. Hence, tuning the interfaces across the heterostructures for desired electrical and magnetic properties is a powerful approach in oxide electronics. Focusing on these aspects, in the present work we employ a novel strategy of engineering the interfaces through the layer stacking sequence and degree of strain to probe the changes occurring in the local atomic environment at the interfaces, magnetic behaviour, and electronic properties of ferromagnetic bilayers La0.7Sr0.3MnO3 (LSMO)/LaCoO3 (LCO) grown by the pulsed laser deposition technique. The biaxial tensile strain experienced by these layers drives the ferromagnetic (FM) ordering temperatures to lower values as compared to their bulk counterparts. Interestingly, the bilayer sequence LCO (15 nm)/LSMO (5 nm) (BL2) exhibits large magnetocrystalline anisotropy (Ku ≈ 4.7 × 104 erg/cc) and weak anti-FM coupling across the interface of the two FM constituents, resulting in a partial compensation in the magnetic moment of the system within a specific temperature window (ΔT = 184 − 82 K). However, for T ≤ 82 K, the FM superexchange interaction between the trivalent Co high-spin and low-spin states dominates the overall magnetic ordering in BL2. The magnetodynamic features probed by the frequency dependent FM resonance (FMR) on this system yield the gyromagnetic ratio (γ/2π ∼ 29.22 GHz/T), demagnetization fields (4πMeff ∼ 3770 Oe), and effective damping constant (αeff ∼ 0.0143) for the BL2 configuration. Moreover, the strength of the nearest-neighbor exchange interaction Jeff in the BL2 configuration exhibits linear falloff with the increasing LCO layer thickness (2 nm ≤tLCO≤ 18 nm). This scenario is also consistent with the variation of the effective number of spins available per unit volume [10 cm−3 ≤ NV(×1022) ≤ 2 cm−3] with increasing tLCO. As tLCO approaches negligibly small values (&lt;2 nm), the magnitude of Jeff/kB reaches its maximum ∼5.47 K (for LCO) and 21.93 K (for LSMO), which is in good agreement with Jeff/kB ∼ 5 ± 2 K (20 ± 2 K) for highly epitaxial LCO (LSMO) single layers. These results demonstrate that the layer sequence control of magnetic coupling across the interfaces opens a constructive approach for exploring the novel electronic devices.

Highlights

INTRODUCTIONScitation.org/journal/adv manipulate the functionalities using both the charge and spin of the layers.[6,7,8,9,10,11,12,13,14,15,16] Our main motivation in choosing the LSMO layer is that it exhibits tunable metal-to-insulator phase transition due to the band filling, large negative magnetoresistance (MR) across the Curie temperature (TC), and induced planar uniaxial anisotropy with a moderate anisotropy field (≈100–500 Oe) grown on the variety of substrates at room temperature.[11,17–28] Multilayers of manganites and cobaltites exhibit recorded magnitudes of MR in which the stacking order of layers plays a major role in the spin polarization of the electrons.[29–31] On the other hand, depending on the ambient pressure, substrate induced strain, and heat-treatment conditions during the synthesis stage, LCO exhibits unusual electronic and magnetic properties
In the present work, we consider the bilayer (BL) heterostructures of ferromagnetic (FM) lanthanum manganite [La0.7Sr0.3MnO3 (LSMO)] and lanthanum cobaltate [LaCoO3 (LCO)] where their functionalities are tuned by interchanging the stacking layers
A considerable in-plane tensile strain induced in STO/LCO is found, which is larger than that of STO/LSMO, even though the lattice mismatch between the LSMO and LCO layers is almost similar in both the altered stacks of heterostructures

Summary

INTRODUCTION

Scitation.org/journal/adv manipulate the functionalities using both the charge and spin of the layers.[6,7,8,9,10,11,12,13,14,15,16] Our main motivation in choosing the LSMO layer is that it exhibits tunable metal-to-insulator phase transition due to the band filling, large negative magnetoresistance (MR) across the Curie temperature (TC), and induced planar uniaxial anisotropy with a moderate anisotropy field (≈100–500 Oe) grown on the variety of substrates at room temperature.[11,17–28] Multilayers of manganites and cobaltites exhibit recorded magnitudes of MR in which the stacking order of layers plays a major role in the spin polarization of the electrons.[29–31] On the other hand, depending on the ambient pressure, substrate induced strain, and heat-treatment conditions during the synthesis stage, LCO exhibits unusual electronic and magnetic properties. LCO gained significant scientific attention in the recent past due to its FM characteristics with TC ≈ 85 K.32 Such FM behavior arises because of the strain driven suppression of the Jahn–Teller distortion with the altered ground state spin configuration (t25ge1g, S = 1 and t24ge2g , S = 2) of trivalent Co between different ranges of temperatures.[17] Density-functional theory (DFT) studies by Kushima et al reported that the lattice strain influences the oxygenvacancy formation and oxygen adsorption, which, in turn, mediates the magneto-elastic and elastoplastic effects in LCO.[33]. Recent studies reveal that the energy conversion efficiency and oxygen reduction/evolution reaction activity of LCO can be enhanced by controlled charge transfer between a LCO thin film and an active layer under the film.[38] All these studies motivated us to investigate the bilayer combination of LSMO and LCO in which one can expect interesting magnetic behavior in the range of 350–360 K and 80–90 K in the vicinity of TC of LSMO and LCO, respectively.[24–27]. All these studies motivated us to investigate the bilayer combination of LSMO and LCO in which one can expect interesting magnetic behavior in the range of 350–360 K and 80–90 K in the vicinity of TC of LSMO and LCO, respectively.[24–27] Since the mixed valency of the cations is very much essential to attain unique magnetotransport properties and robust magnetic behavior in the multilayer systems, in the present work, we bring both trivalent and tetravalent manganese (Mn3+/Mn4+) and trivalent cobalt (Co3+) ions together in a single entity by considering the bilayer configuration of LSMO and LCO systems with different stacking orders.[39]

EXPERIMENTAL DETAILS

RESULTS AND DISCUSSION

SUMMARY