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Helical magnetic state in the vicinity of the pressure-induced superconducting phase in MnP

Sachith E. Dissanayake, Masaaki Matsuda, Kazuyoshi Yoshimi, Shusuke Kasamatsu, Feng Ye, Songxue Chi, William Steinhardt, Gilberto Fabbris, Sara Haravifard, Jinguang Cheng, Jiaqiang Yan, Jun Gouchi, and Yoshiya Uwatoko
Phys. Rev. Research 5, 043026 – Published 10 October 2023
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  • INTRODUCTION
  • PREVIOUS RESULTS
  • EXPERIMENTAL DETAILS
  • EXPERIMENTAL RESULTS
  • THEORETICAL ANALYSIS
  • DISCUSSION
  • SUMMARY
  • ACKNOWLEDGMENTS
    • References

    Abstract

    MnP is a metal that shows successive magnetic transitions from paramagnetic to ferromagnetic and helical magnetic phases at ambient pressure with decreasing temperature. With applied pressure, the magnetic transition temperatures decrease and superconductivity appears around 8 GPa where the magnetic order is fully suppressed and the quantum critical behavior is observed. These results suggest that MnP is an unconventional superconductor in which magnetic fluctuations may be relevant to the superconducting pairing mechanism. In order to elucidate the magnetic ground state adjacent to the superconducting phase first discovered in Mn-based materials, high-pressure neutron diffraction measurements have been performed in hydrostatic pressure up to 7.5 GPa. The helical magnetic structure with the propagation vector along the b axis, reported previously at 3.8 GPa, was found to be robust up to 7.5 GPa. First-principles and classical Monte Carlo calculations have also been performed to understand how the pressure-driven magnetic phase transitions are coupled with change of the exchange interactions. The calculations, which qualitatively reproduce the magnetic structures as a function of pressure, suggest that the exchange interactions change drastically with applied pressure and the further-neighbor interactions become more influential at high pressures. Combining the experimental and theoretical results, we describe the detail of exchange interactions in the vicinity of the superconducting phase, which is critical to understand the pairing mechanism of the unconventional superconductivity in MnP.

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    • Received 26 April 2023
    • Revised 26 August 2023
    • Accepted 1 September 2023

    DOI:https://doi.org/10.1103/PhysRevResearch.5.043026

    Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

    Published by the American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    Exchange interactionHigh-pressure studiesMagnetic order
    1. Physical Systems
    HelimagnetsLow-temperature superconductors
    1. Techniques
    Density functional theoryMonte Carlo methodsNeutron diffractionPressure techniques
    Condensed Matter, Materials & Applied Physics

    Authors & Affiliations

    Sachith E. Dissanayake1,*, Masaaki Matsuda1,†, Kazuyoshi Yoshimi2, Shusuke Kasamatsu3, Feng Ye1, Songxue Chi1, William Steinhardt4, Gilberto Fabbris5, Sara Haravifard4,6, Jinguang Cheng7, Jiaqiang Yan8, Jun Gouchi2, and Yoshiya Uwatoko2

    • 1Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
    • 2Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan
    • 3Faculty of Science, Yamagata University, 1-4-12 Kojirakawa, Yamagata-shi, Yamagata 990-8560, Japan
    • 4Department of Physics, Duke University, Durham, North Carolina 27708, USA
    • 5Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA
    • 6Department of Mechanical Engineering & Materials Science, Duke University, Durham, North Carolina 27708, USA
    • 7Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
    • 8Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA

    • *Present address: Department of Mechanical Engineering, University of Rochester, Rochester, NY 14617.
    • †Corresponding author: matsudam@ornl.gov

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    Vol. 5, Iss. 4 — October - December 2023

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    Images

    • Figure 1
      Figure 1

      (a) The temperature-pressure phase diagram of MnP showing multiple magnetic phases and a superconducting phase. The open and filled circles are data from Cheng et al. (Ref. [7]) and Matsuda et al. (Ref. [9]), respectively. The filled squares have been added in the present study. Note that the pressure is determined at room temperature and it gradually decreases by ∼0.5% at 3 K. (b) The magnetic structure in the ground state at low pressures <1.2GPa (helical c). (c) The magnetic structure at high pressures >3GPa (helical b). The red spheres with blue arrows are Mn atoms, whereas the purple spheres are P ions. The shaded circles represent easy planes. (b) and (c) were created using the VESTA software [11].

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    • Figure 2
      Figure 2

      Exchange interactions J1, J2, J3, and J4 (a) and J5, J6, and J7 (b) in the MnP-type structure. Only magnetic ions are depicted. The figures were created using the VESTA software [11].

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    • Figure 3
      Figure 3

      Incommensurate magnetic Bragg intensity at (0 1−δ 1) measured at (a) 5.5 GPa, (b) 7 GPa, and (d) 7.5 GPa and at (0 1+δ1) measured at (c) 7 GPa. The intensities in (a), (b), and (d) are raw data, whereas those in (c) are the data at 3 K subtracted the 150 K data as a background. Note that a constant background remains due to the temperature-dependent signal from the pressure cell. The solid lines are fits to a Gaussian function. Temperature dependence of the (0 1–δ 1) magnetic Bragg peak intensity measured at (e) 5.5 GPa and (f) 7 GPa. The solid lines are the fitting results to a power-law function. θ−2θ scans of the (011) nuclear Bragg peak at 3 K, just below Tm, and a temperature higher than 200 K measured at (g) 5.5 GPa, (h) 7 GPa, and (i) 7.5 GPa. The measurements at 5.5 and 7 GPa were performed on HB-3 and the measurements at 7.5 GPa were performed on HB-1.

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    • Figure 4
      Figure 4

      (a) Magnetic moment Ma, Mb, and Mc and magnitude of the average moment <|M|> around 3 K as a function of applied pressure. The broken line is a guide to the eye. (b) Incommensurability, δ as a function of pressure for each different magnetic ground state. The different background colors correspond to different magnetic ground states in the phase diagram. Note that the y-error bars are smaller than the symbols. (c) The temperature dependence of δ as a function of pressure. The solid lines are guides to the eye.

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    • Figure 5
      Figure 5

      [(a)–(c)] Temperature dependence of the lattice constants a, c, and b, respectively, measured using neutron diffraction technique as a function of pressure labeled in each panel. (d) Temperature dependence of the lattice constant b at 2.3 and 6 GPa measured using synchrotron x-ray diffraction technique. The solid lines are guides to the eye. The ferromagnetic transition temperature TCurie, the helical c transition temperature Ts, and the helical b transition temperature Tm are marked with arrows. The transition temperatures are derived from the neutron diffraction results shown in Fig. 1. Interpolated values are used for the data in (d). (e) Pressure dependence of the lattice constant b at ∼10 and ∼280K.

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    • Figure 6
      Figure 6

      The calculated pressure dependence of the magnetic moment per MnP unit in the collinear ferromagnetic structure.

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    • Figure 7
      Figure 7

      The calculated pressure dependence of the exchange interactions J up to the ninth-nearest neighbor. Positive and negative values correspond to ferromagnetic and antiferromagnetic interactions, respectively.

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    • Figure 8
      Figure 8

      The calculated exchange interactions J up to the 51st-nearest neighbor plotted vs bond distance. Positive and negative values correspond to ferromagnetic and antiferromagnetic interactions, respectively. Dashed horizontal lines are drawn at ±0.5meV as guides for the eye. The inset shows an expanded figure in the range of −1meV<J<1meV.

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    • Figure 9
      Figure 9

      The snapshots of magnetic structures obtained at 1.8×105 MC step under the pressure P=0, 1.25, 2.94, 3.20, 5.29, 6.43, 7.41, 9.00, and 10.29 GPa for Jmin=0.01, 0.1, 0.5, and 1 meV, respectively. Red and blue represent spins with Sz components of 1 and −1 along the c axis, respectively [50].

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    • Figure 10
      Figure 10

      (a) The snapshots of magnetic structures obtained at 1.8×105 MC step for T=10, 100, 200, and 300 K under the pressure P=0, 1.25, 2.94, 3.20, 5.29, 6.43, 7.41, 9.00, and 10.29 GPa with Jmin=0.5meV. The enlarged figures of the snapshots of magnetic structures for (b) P=0GPa, (c) P=1.25GPa, and (d) P=6.43GPa at T=10K. Red and blue represent spins with Sz components of 1 and −1 along the c axis, respectively [50].

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