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Surfaces, Interfaces, and Applications
Strain-Enhanced Charge Transfer and Magnetism at Manganite/Nickelate Interface Zedong Xu, Songbai Hu, Rui Wu, Jiaou Wang, Tom Wu, and Lang Chen ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b06949 • Publication Date (Web): 21 Aug 2018 Downloaded from http://pubs.acs.org on August 22, 2018
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ACS Applied Materials & Interfaces
Strain-Enhanced
Charge
Transfer
and
Magnetism
at
Manganite/Nickelate Interface Zedong Xu,*,† Songbai Hu,† Rui Wu,‡ Jia-Ou Wang,‡ Tom Wu,§ Lang Chen*,† †
Department of Physics, Southern University of Science and Technology, Shenzhen, Guangdong
518055, China. ‡
Laboratory of Synchrotron Radiation, Institute of High Energy Physics, Chinese Academy of
Sciences, Beijing 100039, China. §
School of Materials Science and Engineering, UNSW Australia, Sydney New South Wales 2052,
Australia. ABSTRACT: Strain effect on the charge transfer in correlated oxide La0.8Sr0.2MnO3/NdNiO3 (LSMO/NNO) heterostructures is investigated. This is achieved by carefully tailoring the strain on the two layers using various substrates. In contrast to bare LSMO films, the strain dependence of the enhanced magnetic moment of the LSMO/NNO bilayers strongly suggests that the charge transfer can be controlled via strain engineering in complex oxide heterostructures. Furthermore, our study also reveals that the coercive field, exchange bias and conductivity are dramatically affected by the strain-modulated charge transfer in LSMO/NNO heterostructures. Our work thus point out a new path to control electronic states in oxide heterostructures to advance the use of interface in oxide-based electronics. KEYWORDS: complex oxide heterostructures, interface engineering, strain effect, charge transfer, enhanced magnetism
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1.
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INTRODUCTION Interface engineering often brings about novel physical properties unattainable in the bulk
materials. Such emergent properties are often modified by the interfacial mismatches in lattice, composition and/or valence state, 1, 2 leading to electronic, spin and structural reconstructions. One classic example is the interface between two insulators, LaAlO3 and SrTiO3, which possesses two-dimensional electron gas due to unusual electronic reconstruction.3 Rational design and control of various reconstructions in charge, spin, orbit and structure degrees of freedom is the key to tailoring the properties of artificial heterostructures. Charge transfer is ubiquitous at hetero-interfaces, which often causes a dramatic change of interfacial properties. And the manipulation of the electronic behavior would advance the use of heterointerface in oxide-based electronics. In strongly correlated oxide manganite/nickelate heterostructures, charge transfer results in the appearance of additional interfacial electronic states, i.e., Mn3+ (t2g3eg1) + Ni3+ (t2g6eg1)→ Mn4+ (t2g3eg0) + Ni2+ (t2g6eg2),4-7 which profoundly affects the electric and magnetic properties of manganites. What is less known, however, is how external strain
would
affect
the
interface
charge
transfer
process.
Here,
we
employ
the
La1-xSrxMnO3/NdNiO3 (LSMO/NNO) heterostructures deposited on various substrates to clarify this question. The La0.8Sr0.2MnO3 composition is chosen because it lies near the boundary between an insulating antiferromagnetic (AFM) and a metallic ferromagnetic (FM) ground states in bulk phase diagram.8 A set of perovskite oxide single-crystal substrates are used to exert various strains on the LSMO/NNO heterostructures, while bare LSMO films on the same substrates are used as references. It is observed that charge transfer at the interface can be tuned by strain in both compressive and tensile regions (with respect to LSMO film). Furthermore, it is observed that the 2 / 23
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ACS Applied Materials & Interfaces
tensile strain leads to more obvious effect than compressive one in the bilayers. 2.
EXPERIMENTAL SECTION The epitaxial single layer LSMO (15 u.c.) and NNO (10 u.c.) and LSMO/NNO (15/10 u.c.)
heterostructures were grown by the pulsed laser deposition (PLD) method on a series of (001)-oriented
perovskite
single-crystal
substrates,
including
LaAlO3
(LAO),
(La0.3Sr0.7)(Al0.65Ta0.35)O3 (LAST), SrTiO3 (STO) and KTaO3 (KTO). All of the films were grown at 700 °C with an oxygen pressure of 200 mTorr to avoid any change of oxygen vacancies density at the interface. The 2 J cm-2 of laser fluence is applied with a repetition rate of 1 Hz. Before deposition, low miscut (
