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Net Magnetization and Inhomogeneous Magnetic Order in a High-Tc Nickelate Superconductor

Alexander J. Grutter, Nurul Fitriyah, Brian B. Maranville, Saurav Prakash, Andreas Suter, Jochen Stahn, Gianluca Janka, Xing Gao, King Yau Yip, Zaher Salman, Thomas Prokscha, Julie A. Borchers, Ariando Ariando

TL;DR

The study investigates how magnetism intertwines with high-temperature superconductivity in the infinite-layer nickelate SECNO using depth-resolved LEμSR and PNR. LEμSR reveals a disordered, inhomogeneous magnetic state that begins freezing around $T\approx 200$ K and evolves toward a static limit, while PNR uncovers a substantial, nonuniform net magnetization ($M\sim 55$ kA/m at the film surface) that persists across the superconducting transition at $T_c$. The magnetization is concentrated near the film surface and is best described by a two-layer SECNO magnetic structure, indicating coexistence of ferromagnetic-like order with superconductivity rather than a uniform magnetic phase. These results, together with the influence of Eu doping and substrate effects, provide new insights into the magnetic environment of nickelate superconductors and its possible role in the observed high-field re-entrant superconductivity.

Abstract

High-temperature and high-magnetic-field-induced re-entrant superconductivity has been discovered in the infinite-layer nickelate $\mathrm{Sm_{1-x-y} Eu_x Ca_y Ni O_2}$ (SECNO). Infinite-layer nickelates are the closest known analogues of high-$\mathrm{T}_c$ cuprate superconductors, yet they host distinct magnetic ground states. Using low-energy muon spin relaxation and polarized neutron reflectometry, we reveal the magnetic order in SECNO. We find that magnetic freezing occurs at a higher-temperature than in other nickelate compounds, and that a substantial net magnetization of 55 $\,\mathrm{kA}\,\mathrm{m}^{-1}$ $\pm10 \,\mathrm{kA}\,\mathrm{m}^{-1}$ emerges and remains largely unchanged across the superconducting transition. The magnetism in SECNO is disordered and nonuniform.

Net Magnetization and Inhomogeneous Magnetic Order in a High-Tc Nickelate Superconductor

TL;DR

The study investigates how magnetism intertwines with high-temperature superconductivity in the infinite-layer nickelate SECNO using depth-resolved LEμSR and PNR. LEμSR reveals a disordered, inhomogeneous magnetic state that begins freezing around K and evolves toward a static limit, while PNR uncovers a substantial, nonuniform net magnetization ( kA/m at the film surface) that persists across the superconducting transition at . The magnetization is concentrated near the film surface and is best described by a two-layer SECNO magnetic structure, indicating coexistence of ferromagnetic-like order with superconductivity rather than a uniform magnetic phase. These results, together with the influence of Eu doping and substrate effects, provide new insights into the magnetic environment of nickelate superconductors and its possible role in the observed high-field re-entrant superconductivity.

Abstract

High-temperature and high-magnetic-field-induced re-entrant superconductivity has been discovered in the infinite-layer nickelate (SECNO). Infinite-layer nickelates are the closest known analogues of high- cuprate superconductors, yet they host distinct magnetic ground states. Using low-energy muon spin relaxation and polarized neutron reflectometry, we reveal the magnetic order in SECNO. We find that magnetic freezing occurs at a higher-temperature than in other nickelate compounds, and that a substantial net magnetization of 55 emerges and remains largely unchanged across the superconducting transition. The magnetism in SECNO is disordered and nonuniform.

Paper Structure

This paper contains 15 sections, 4 equations, 14 figures, 1 table.

Table of Contents

  1. Experimental Methods
  2. Sample Synthesis
  3. Electrical Transport
  4. X-ray Diffraction
  5. Low-Energy Muon Spin Relaxation
  6. Neutron Reflectometry
  7. Supplemental Information
  8. Additional Low-energy Muon Spin Relaxation (LE$\mu$SR) Analysis and Information
  9. $\mathrm{LCNO}$ implantation profiles and measurement
  10. Characterization of $\mathrm{NdGaO_3}$ substrates
  11. $\mathrm{SECNO}$ and $\mathrm{LCNO}$ wTF LE$\mu$SR energy dependence
  12. Additional zero-field (ZF) LE$\mu$SR data and analysis
  13. Note on the influence of substrates in LE$\mu$SR
  14. Polarized Neutron Reflectometry Analysis
  15. LCNO Transport

Figures (14)

  • Figure 1: (a) Resistance, normalized to the value at 300 K, vs. temperature for the samples used in this study. (b) Close-up view of the temperature range encompassing the superconducting transitions of all samples, emphasizing the narrow distribution of transition temperatures. (c) x-ray diffraction measurement of s35, showing Laue fringes from the film and 00L film diffraction peaks consistent with a c-axis lattice constant of approximately 3.26 Å. Substrate peaks indexed using the pseudocubic (pc) unit cell.
  • Figure 2: (a) Simulated muon implantation distribution vs. depth for the SECNO mosaic, using average thickness values. (b) Fraction of implanted muons stopping in each layer. (c) ZF LE$\mu$SR asymmetry vs. time for the SECNO mosaic at selected temperatures. (d) ZF LE$\mu$SR asymmetry vs. time for the LCNO sample at selected temperatures. (e) Stretching parameter ($\beta$) from fits to the ZF asymmetry vs. temperature. (f) Fitted ZF muon polarization relaxation rate ($\lambda_{\rm S}$) vs. temperature. (g) Representative wTF LE$\mu$SR asymmetry vs. time for the SECNO mosaic in 10 mT applied field at $300\,\mathrm{K}$ and $4\,\mathrm{K}$, alongside theoretical fits. (h) F$_M$ vs. temperature for SECNO and LCNO. (i) wTF muon polarization relaxation rate for SECNO, LCNO, and NGO substrate vs. temperature. Error bars represent $\pm 1$ standard deviation.
  • Figure 3: (a) Spin-dependent neutron reflectivity, normalized by theoretical substrate reflectivity, vs. $Q_Z$, alongside theoretical fits. Curves offset for visual clarity. (b) Spin asymmetry vs. $Q_Z$ calculated from the data in (a), alongside theoretical curves. Curves offset for visual clarity. (c) Best-fit nuclear and magnetic neutron scattering length densities vs. distance from the NGO/SECNO interface ($Z$), based on model with two distinct magnetic regions in the SECNO. Error bars represent $\pm1$ standard deviation.
  • Figure S1: (a) Simulated muon implantation distribution vs. depth for the LCNO sample. (b) Fraction of implanted muons stopping in each layer.
  • Figure S2: (a) Temperature-dependent LE$\mu$SR asymmetry from NGO substrates at implantation energies of 1 keV, 2.5 keV, and 18 keV. (b) Calculated F$_M$ for NGO for 1 keV muons. (c) Raw F$_M$ from the SECNO mosaic and the corrected F$_M$ after subtracting the contribution from muons stopping in the NGO substrate. The rescaled curve shown in the main text is obtained by dividing the corrected data by the fraction of muons stopping in the STO and SECNO. (d) Muon polarization relaxation rate vs. temperature for SECNO and NGO mosaics at 1 keV implantation energy. Error bars represent $\pm$1 standard deviation.
  • ...and 9 more figures