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Title: Orientation Control of Interfacial Magnetism at La 0.67Sr 0.33MnO 3/SrTiO 3 Interfaces

Abstract

Understanding the magnetism at the interface between a ferromagnet and an insulator is essential because the commonly posited magnetic “dead” layer close to an interface can be problematic in magnetic tunnel junctions. Previously, degradation of the magnetic interface was attributed to charge discontinuity across the interface. In this paper, the interfacial magnetism was investigated using three identically prepared La 0.67Sr 0.33MnO 3 (LSMO) thin films grown on different oriented SrTiO 3 (STO) substrates by polarized neutron reflectometry. In all cases the magnetization at the LSMO/STO interface is larger than the film bulk. We show that the interfacial magnetization is largest across the LSMO/STO interfaces with (001) and (111) orientations, which have the largest net charge discontinuities across the interfaces. In contrast, the magnetization of LSMO/STO across the (110) interface, the orientation with no net charge discontinuity, is the smallest of the three orientations. We show that a magnetically degraded interface is not intrinsic to LSMO/STO heterostructures. Finally, the approach to use different crystallographic orientations provides a means to investigate the influence of charge discontinuity on the interfacial magnetization.

Authors:
ORCiD logo [1];  [1];  [2];  [1]; ORCiD logo [3];  [4]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Quantum Condensed Matter Division
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Instruments and Source Division
  3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Materials Science and Technology Division
  4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Quantum Condensed Matter Division; Univ. of Tennessee, Knoxville, TN (United States). Dept. of Physics and Astronomy
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); USDOE Laboratory Directed Research and Development (LDRD) Program
Contributing Org.:
Univ. of Tennessee, Knoxville, TN (United States)
OSTI Identifier:
1362256
Grant/Contract Number:
AC05-00OR22725
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
ACS Applied Materials and Interfaces
Additional Journal Information:
Journal Volume: 9; Journal Issue: 22; Journal ID: ISSN 1944-8244
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; charge discontinuity; interfacial magnetization; magnetic “dead” layer; polarized neutron reflectometry

Citation Formats

Guo, Er-Jia, Charlton, Timothy, Ambaye, Haile, Desautels, Ryan D., Lee, Ho Nyung, and Fitzsimmons, Michael R.. Orientation Control of Interfacial Magnetism at La0.67Sr0.33MnO3/SrTiO3 Interfaces. United States: N. p., 2017. Web. doi:10.1021/acsami.7b03252.
Guo, Er-Jia, Charlton, Timothy, Ambaye, Haile, Desautels, Ryan D., Lee, Ho Nyung, & Fitzsimmons, Michael R.. Orientation Control of Interfacial Magnetism at La0.67Sr0.33MnO3/SrTiO3 Interfaces. United States. doi:10.1021/acsami.7b03252.
Guo, Er-Jia, Charlton, Timothy, Ambaye, Haile, Desautels, Ryan D., Lee, Ho Nyung, and Fitzsimmons, Michael R.. Tue . "Orientation Control of Interfacial Magnetism at La0.67Sr0.33MnO3/SrTiO3 Interfaces". United States. doi:10.1021/acsami.7b03252. https://www.osti.gov/servlets/purl/1362256.
@article{osti_1362256,
title = {Orientation Control of Interfacial Magnetism at La0.67Sr0.33MnO3/SrTiO3 Interfaces},
author = {Guo, Er-Jia and Charlton, Timothy and Ambaye, Haile and Desautels, Ryan D. and Lee, Ho Nyung and Fitzsimmons, Michael R.},
abstractNote = {Understanding the magnetism at the interface between a ferromagnet and an insulator is essential because the commonly posited magnetic “dead” layer close to an interface can be problematic in magnetic tunnel junctions. Previously, degradation of the magnetic interface was attributed to charge discontinuity across the interface. In this paper, the interfacial magnetism was investigated using three identically prepared La0.67Sr0.33MnO3 (LSMO) thin films grown on different oriented SrTiO3 (STO) substrates by polarized neutron reflectometry. In all cases the magnetization at the LSMO/STO interface is larger than the film bulk. We show that the interfacial magnetization is largest across the LSMO/STO interfaces with (001) and (111) orientations, which have the largest net charge discontinuities across the interfaces. In contrast, the magnetization of LSMO/STO across the (110) interface, the orientation with no net charge discontinuity, is the smallest of the three orientations. We show that a magnetically degraded interface is not intrinsic to LSMO/STO heterostructures. Finally, the approach to use different crystallographic orientations provides a means to investigate the influence of charge discontinuity on the interfacial magnetization.},
doi = {10.1021/acsami.7b03252},
journal = {ACS Applied Materials and Interfaces},
number = 22,
volume = 9,
place = {United States},
year = {Tue May 16 00:00:00 EDT 2017},
month = {Tue May 16 00:00:00 EDT 2017}
}

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  • The dead-layer behavior, deterioration of the bulk properties in near-interface layers, restricts the applications of many oxide heterostructures. We present the systematic study of the dead-layer in La{sub 0.67}Sr{sub 0.33}MnO{sub 3}/SrTiO{sub 3} grown by ozone-assisted molecular beam epitaxy. Dead-layer behavior is systematically tuned by varying the interfacial doping, while unchanged with varied doping at any other atomic layers. In situ photoemission and low energy electron diffraction measurements suggest intrinsic oxygen vacancies at the surface of ultra-thin La{sub 0.67}Sr{sub 0.33}MnO{sub 3}, which are more concentrated in thinner films. Our results show correlation between interfacial doping, oxygen vacancies, and the dead-layer, whichmore » can be explained by a simplified electrostatic model.« less
  • We demonstrate reversible control of magnetization and anisotropy in La 0.67Sr 0.33MnO 3 films through interfacial oxygen migration. Gd metal capping layers deposited onto La 0.67Sr 0.33MnO 3 leach oxygen from the film through a solid-state redox reaction to form porous Gd 2O 3. X-ray absorption and polarized neutron reflectometry measurements show Mn valence alterations consistent with high oxygen vacancy concentrations, resulting in suppressed magnetization and increased coercive fields. Effects of the oxygen migration are observed both at the interface and also throughout the majority of a 40 nm thick film, suggesting extensive diffusion of oxygen vacancies. After Gd-capped Lamore » 0.67Sr 0.33MnO 3 is exposed to atmospheric oxygen for a prolonged period of time, oxygen diffuses through the Gd 2O 3 layer and the magnetization of the La 0.67Sr 0.33MnO 3 returns to the uncapped value. In conclusion, these findings showcase perovskite heterostructures as ideal candidates for developing functional interfaces through chemically-induced oxygen migration.« less
  • La{sub 0.67}Sr{sub 0.33}MnO{sub 3-{delta}} films, fabricated on (1 1 1) LaAlO{sub 3} single-crystal substrates using a direct current magnetron sputtering technique, are demonstrated by X-ray diffraction patterns and pole figures to be high quality epitaxial films and there is a perfect matching relationship between the films and the substrates. We observed an obvious difference of the electronic-magnetic transportation properties among films sputtered on (1 1 1) (1 0 0) and (1 1 0) LaAlO{sub 3} substrates, respectively. A mechanism for the difference is discussed briefly.
  • Using ferromagnetic La{sub 0.67}Sr{sub 0.33}MnO{sub 3} electrodes bridged by single-layer graphene, we observe magnetoresistive changes of ∼32–35 MΩ at 5 K. Magneto-optical Kerr effect microscopy at the same temperature reveals that the magnetoresistance arises from in-plane reorientations of electrode magnetization, evidencing tunnelling anisotropic magnetoresistance at the La{sub 0.67}Sr{sub 0.33}MnO{sub 3}-graphene interfaces. Large resistance switching without spin transport through the non-magnetic channel could be attractive for graphene-based magnetic-sensing applications.
  • The interfacial spin state of the multiferroic heterostructure PbZr{sub 0.52}Ti{sub 0.48}O{sub 3}/La{sub 0.67}Sr{sub 0.33}MnO{sub 3} and its dependence on ferroelectric polarization is investigated with magnetic second-harmonic generation at 78 K. The spin alignment of Mn ions in the first unit cell layer at the heterointerface can be tuned from ferromagnetic to antiferromagnetic exchange coupled, while the bulk magnetization remains unchanged. Multiple domains of both phases coexist as the ferroelectric polarization is switched. The results will help promote the development of new interface-based functionalities and device concepts.