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Magnetic frustration driven by conduction carrier blocking in Nd2Co0.85Si2.88

Mily Kundu, Santanu Pakhira, Renu Choudhary, Shuvankar Gupta, Sudip Chakraborty, N. Lakshminarasimhan, R. Ranganathan, Duane D. Johnson, and Chandan Mazumdar
Phys. Rev. B 107, 094421 – Published 17 March 2023
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  • INTRODUCTION
  • EXPERIMENTAL DETAILS
  • COMPUTATIONAL DETAILS
  • RESULTS AND DISCUSSIONS
  • CONCLUDING REMARKS
  • ACKNOWLEDGMENTS
    • References

    Abstract

    The intermetallic compound Nd2Co0.85Si2.88 having a triangular lattice could be synthesized in single phase only with defect crystal structure. Investigation through different experimental techniques indicate the presence of two magnetic transitions in the system. As verified experimentally and theoretically, the high-temperature transition TH∼ 140 K is associated with the development of ferromagnetic interaction between itinerant Co moments, whereas the low-temperature transition at TL∼ 6.5 K is due to the coupling among Nd−4f and Co−3d moments, which is antiferromagnetic in nature. Detailed studies of temperature-dependent dc magnetic susceptibility, field dependence of isothermal magnetization, nonequilibrium dynamical behavior, viz., magnetic relaxation, aging effect, magnetic-memory effect, and temperature dependence of heat capacity, along with density functional theory (DFT) calculations, suggest that the ground state is magnetically frustrated spin glass in nature, having competing magnetic interactions of equivalent energies. DFT results further reveal that the 3d/5d-conduction carriers are blocked in the system and act as a barrier for the 4f−4f RKKY interactions, resulting in spin frustration. Presence of vacancy defects in the crystal are also conducive to the spin frustration. This is an unique mechanism of magnetic frustration, not emphasized so far in any of the ternary R2TX3 (R = rare earth, T = transition elements, and X = Si, Ge, In) type compounds. Due to the competing character of the itinerant 3d and localized 4f moments, the compound exhibits anomalous field dependence of magnetic coercivity. The system also exhibits a considerable magnetic entropy change of −ΔSM∼ 13.3 J/kg K with a relative cooling power (RCP) of 220 J/kg and adiabatic temperature change ΔTad of 6 K for magnetic field change of 70 kOe.

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    • Received 17 November 2021
    • Revised 16 November 2022
    • Accepted 27 February 2023

    DOI:https://doi.org/10.1103/PhysRevB.107.094421

    ©2023 American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    AntiferromagnetismFerromagnetismFrustrated magnetismMagnetic susceptibilityMagnetismRKKY interactionSpecific heat
    1. Physical Systems
    AntiferromagnetsSpin glassesStrongly correlated systems
    1. Techniques
    CrystallographyDensity functional theorySpecific heat measurementsSusceptibility measurementsX-ray diffraction
    Condensed Matter, Materials & Applied Physics

    Authors & Affiliations

    Mily Kundu1, Santanu Pakhira1,2,*, Renu Choudhary2, Shuvankar Gupta1, Sudip Chakraborty1, N. Lakshminarasimhan3,4, R. Ranganathan1, Duane D. Johnson2,5, and Chandan Mazumdar1

    • 1Condensed Matter Physics Division, Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata 700064, India
    • 2Ames Laboratory, Iowa State University, Ames, Iowa 50011, USA
    • 3Electro-organic and Materials Electrochemistry Division, CSIR-Central Electrochemical Research Institute, Karaikudi 630 003, India
    • 4Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201 002, India
    • 5Department of Materials Science & Engineering, Iowa State University, Ames, Iowa 50011, USA

    • *Corresponding author: spakhira@ameslab.gov

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    Vol. 107, Iss. 9 — 1 March 2023

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    Images

    • Figure 1
      Figure 1

      Crystal structure of Nd2Co0.85Si2.88 belonging to the U2RuSi3-type structure (space group: P6/mmm), which is a superstructure of AlB2-type structure.

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    • Figure 2
      Figure 2

      (a) Room temperature XRD pattern of Nd2CoSi3. (b) The XRD patterns of Nd2Co0.85Si2.88 at T = 300 K (top) and T = 15 K (bottom) along with full-Rietveld analysis. Top inset shows the major peaks associated with the secondary phase NdCoSi2 that is absent in defect formation. Bottom inset presents the temperature dependence of unit-cell volume along with fit using Eq. (1). Estimated errors are smaller than the symbol size.

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    • Figure 3
      Figure 3

      (a) Backscattered electron (BSE) image and [(b)–(d)] elemental mapping by SEM equipped with EDX on the polished surface of Nd2Co0.85Si2.88 from the region presented in (a). (e) EDX results of Nd2Co0.85Si2.88.

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    • Figure 4
      Figure 4

      (a) Left panel shows the temperature dependence of susceptibility (χ) in ZFC and FC protocol at H=0.1 kOe and right panel represents the inverse susceptibility data for FC measurement. Inset shows an expanded view of χ(T) for both the ZFC and FC configuration at low temperature region. (b) χ(T) in ZFC and FC protocol for various applied magnetic fields. The data are separated from each other manually to have a clear view. (c) χ−1(T) for FC mode at different magnetic fields. Curie-Weiss fitting of χ−1(T) is presented for 160–300 K at H=1 kOe.

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    • Figure 5
      Figure 5

      (a) Magnetic field dependence of magnetization at different temperatures. Inset shows the isothermal magnetization curve at T = 2 K along with the estimated FM and AFM/PM contributions. (b) Isothermal magnetization at some selected temperatures, T = (I) 2 K; (II) 30 K; (III) 100 K, and (IV) 140 K, close to the low field region. (c) Temperature dependence of coercive field. Solid line is guide to the eye.

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    • Figure 6
      Figure 6

      (a) Zero-field heat capacity of Nd2Co0.85Si2.88 and its non-magnetic analog La2Co0.99Si2.99. The magnetic contribution to the heat capacity (left panel) and magnetic entropy (right panel) as a function of temperature have been estimated by subtracting the non-magnetic contribution. (Top inset) The experimental C(T) data in the region of magnetic ordering. (Bottom inset) The expanded view of magnetic contribution for a limited range of temperature. (b) Heat capacity of Nd2Co0.85Si2.88 fitted using Eq. (8).

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    • Figure 7
      Figure 7

      Nd−4f spin configuration in Nd2CoSi3 (pseudoprimitive): I, Nd1 and Nd2 are antiparallel; II, one Nd-atom at site-2 is antiparallel to others; III, Nd spins of both sites are parallel.

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    • Figure 8
      Figure 8

      Configurations I and III from the Fig. 7 are extended into 2×1×1 supercell. IV and V are newly added configurations.

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    • Figure 9
      Figure 9

      Configurations I and III from Fig. 7 are extended into 1×1×2 supercell. VI, VII, and VIII are newly added configurations.

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    • Figure 10
      Figure 10

      Spin-polarized local density of states (LDOS) of Nd2CoSi3 with spin structure-III (see Fig. 7) for (a) 4f and 3d states of Nd and Co, (b) 3p, 3d, 5d, and 4f states showing hybridization. Note: Nd−5d and Si−3p states are magnified by a factor of 5 and 2, respectively, in the figure.

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    • Figure 11
      Figure 11

      (a) Time-dependent normalized magnetization of Nd2Co0.85Si2.88 at T = 2 K under ZFC protocol for different wait times, along with stretched exponential fit [Eq. (13)]. (b) The relaxation rate S(t) at T = 2 K for two different wait times in ZFC protocol for Nd2Co0.85Si2.88, exhibiting aging phenomenon.

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    • Figure 12
      Figure 12

      (a) Magnetic relaxation rate as a function of time on a log-log plot for Nd2Co0.85Si2.88 at different temperatures obtained from the corresponding ZFC magnetic relaxations in a 100 Oe field as shown in the inset. The straight lines correspond to the linear fit following Eq. (15) and the exponent values n are determined from the slopes of the fit. (b) Time dependence of magnetic relaxation rate on a log-log plot at 2 K for different magnetic fields, obtained from corresponding ZFC magnetic relaxations as shown in the inset. The exponent values n for different fields are determined from the linear fits [Eq. (15)] to the relaxation rate.

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    • Figure 13
      Figure 13

      Magnetic memory effect of Nd2Co0.85Si2.88 in (a) field-cooled (FC) condition and (b) zero-field-cooled (ZFC) condition for 100 Oe applied field.

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    • Figure 14
      Figure 14

      Magnetic relaxation behavior of Nd2Co0.85Si2.88 at 4 K for H = 100 Oe with temporary cooling at 2 K in (a) FC method and (b) ZFC method. Magnetic relaxation behavior at 4 K with an opposite relaxation during temporary cooling at 2 K using (c) the FC and (d) ZFC protocol. The insets present the relaxation data as a function of total time spent at 4 K along with the fit (solid red line) using stretched exponential function [Eq. (13)].

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    • Figure 15
      Figure 15

      Magnetic relaxation behavior of Nd2Co0.85Si2.88 at 4 K with temporary heating at 6 K measured using ZFC and FC protocol for H = 100 Oe.

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    • Figure 16
      Figure 16

      Field dependence of isothermal magnetization for Nd2Co0.85Si2.88 at different temperatures during field change 0 Oe → 70 kOe.

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    • Figure 17
      Figure 17

      Temperature dependence of isothermal magnetic entropy change (−ΔSM) for Nd2Co0.85Si2.88 at different applied magnetic fields. Inset presents Relative cooling power (RCP) as a function of applied field changes.

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    • Figure 18
      Figure 18

      Temperature dependence of adiabatic temperature change (ΔTad) of Nd2Co0.85Si2.88 for different magnetic fields.

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