Sudden Collapse of Magnetic Order in Oxygen-Deficient Nickelate Films

Jiarui Li, Robert J. Green, Zhen Zhang, Ronny Sutarto, Jerzy T. Sadowski, Zhihai Zhu, Grace Zhang, Da Zhou, Yifei Sun, Feizhou He, Shriram Ramanathan, and Riccardo Comin

Phys. Rev. Lett. 126, 187602 – Published 6 May 2021

Abstract

Antiferromagnetic order is a common and robust ground state in the parent (undoped) phase of several strongly correlated electron systems. The progressive weakening of antiferromagnetic correlations upon doping paves the way for a variety of emergent many-electron phenomena including unconventional superconductivity, colossal magnetoresistance, and collective charge-spin-orbital ordering. In this study, we explored the use of oxygen stoichiometry as an alternative pathway to modify the coupled magnetic and electronic ground state in the family of rare earth nickelates ( ${RENiO}_{3 - x}$ ). Using a combination of x-ray spectroscopy and resonant soft x-ray magnetic scattering, we find that, while oxygen vacancies rapidly alter the electronic configuration within the Ni and O orbital manifolds, antiferromagnetic order is remarkably robust to substantial levels of carrier doping, only to suddenly collapse beyond 0.21 $e^{-} / Ni$ without an accompanying structural transition. Our work demonstrates that ordered magnetism in ${RENiO}_{3 - x}$ is mostly insensitive to carrier doping up to significant levels unseen in other transition-metal oxides. The sudden collapse of ordered magnetism upon oxygen removal may provide a new mechanism for solid-state magnetoionic switching and new applications in antiferromagnetic spintronics.

Received 12 June 2020
Revised 17 October 2020
Accepted 17 March 2021

DOI:https://doi.org/10.1103/PhysRevLett.126.187602

Physics Subject Headings (PhySH)

Electronic structure

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Jiarui Li ¹, Robert J. Green^2,3, Zhen Zhang⁴, Ronny Sutarto ⁵, Jerzy T. Sadowski ⁶, Zhihai Zhu¹, Grace Zhang¹, Da Zhou ^1,7, Yifei Sun⁴, Feizhou He⁵, Shriram Ramanathan⁴, and Riccardo Comin^1,*

¹Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
²Department of Physics and Engineering Physics, University of Saskatchewan, Saskatoon, Saskatchewan, Canada S7N 5E2
³Stewart Blusson Quantum Matter Institute, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4
⁴School of Materials Engineering, Purdue University, West Lafayette, Indiana 47907, USA
⁵Canadian Light Source, Saskatoon, Saskatchewan S7N 2V3, Canada
⁶Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973, USA
⁷School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China

^*rcomin@mit.edu

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Issue

Vol. 126, Iss. 18 — 7 May 2021

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Images

Figure 1
(a) Measured (solid) and simulated (dashed) x-ray absorption spectra across the Ni $L_{2, 3}$ edges for ${SmNiO}_{3 - x}$ with different electron-doping levels, obtained by annealing stoichiometric films in an oxygen deficient atmosphere. The doping level (number of doped electrons per Ni) is specified for each simulated spectrum. Spectra are vertically offset for clarity. (b) x-ray absorption spectra across the O $K$ edges for the same ${SmNiO}_{3 - x}$ samples. The same color legend is used as the data series in Fig. 1. (c) The doping levels vs annealing time for each sample, as extracted from the comparison between experimental and theoretical spectra. Vertical error bars reflect the uncertainty in the doping level for each sample.
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Figure 2
(top) Double cluster electronic model for ${RENiO}_{3}$ . The alternating expanded and compressed ${NiO}_{6}$ octahedra, inequivalent Ni $3 d$ orbital occupation, and unbalanced O $2 p$ orbitals are highlighted. (a)–(c) Doping evolution of the ${SmNiO}_{3 - x}$ electronic structure from double cluster simulation. The evolution of different physical quantities for the two inequivalent sites are shown: (a) occupation of Ni $3 d$ orbitals; (b) number of ligand holes; (c) magnitude of Ni spin moments. The charge and bond disproportionation magnitudes as defined in Eq. (1) are marked out by arrows in (a), (b), respectively. (d) The configuration weights of the ground-state wave function decomposed into states with different total electron filling ( $f^{6}$ , $f^{7}$ , $f^{8}$ ) as a function of doping.
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Figure 3
(a) Rocking curves as a function of sample angle theta, across the $Q_{AFM} = (1 / 4, 1 / 4, 1 / 4)_{pc}$ AFM reflection in ${SmNiO}_{3 - x}$ at 22 K (colored solid line) and 300 K (gray dashed line). The same color legend is used as the XAS data series in Fig. 1. Curves are vertically offset for clarity. The intensity of the last three curves was rescaled to highlight that no scattering signal could be detected above the noise level. (b) Doping dependence of the AFM ordering temperature ( $T_{AFM}$ ). The $T_{AFM}$ is determined by the temperature when the magnetic peak intensity falls below the noise level. (c) Doping dependence of the magnetic Bragg peak intensity and correlation length measured at 22 K. The dashed line is a linear fit to the data points from samples with AFM order and extrapolates to a threshold doping $n = 0.21$ for the sudden collapse of magnetic order. Note that the vertical error bar is smaller than the marker.
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Figure 4
(a) Temperature dependence of the AFM ordering peak integrated intensity in ${SmNiO}_{3 - x}$ . The intensity for the magnetic ordered samples are normalized to the lowest temperature. The same color legend is used as the XAS data series in Fig. 1. (b) Temperature-doping plot of the magnetic phase diagram in ${SmNiO}_{3 - x}$ . The magnetic scattering intensity is color coded in the background. The AFM transition temperature for each sample is marked out. The striped area highlights the temperature range that cannot be accessed in our study.
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