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Hidden frustration in the triangular-lattice antiferromagnet NdCd3P3

Juan R. Chamorro, Steven J. Gomez Alvarado, Dibyata Rout, Sarah Schwarz, Allen Scheie, Ganesh Pokharel, Alexander I. Kolesnikov, Lukas Keller, Stephen D. Wilson

Abstract

We report a study of the magnetic ground state and crystal electric field (CEF) scheme in the triangular-lattice antiferromagnet NdCd$_3$P$_3$. Combined neutron scattering, magnetization, and heat capacity measurements demonstrate that the Nd$^{3+}$ moments occupying the triangular lattice in this material harbor hidden signs of frustration not detected in typical Curie-Weiss-based parameterization of the frustration index ($f=Θ_{CW} / T_N$). This is evidenced by a zero-field splitting of the Kramers' ground state and first excited state doublets at temperatures far in excess of $T_N$ as well as signatures of low-energy fluctuations for $T>>T_N$. A suppression of the zero-field ordered moment relative to its field saturation value is observed, and the impacts of this magnetic frustration as well as the coexisting bond frustration in the CdP honeycomb network on the physical properties of NdCd$_3$P$_3$ are discussed.

Hidden frustration in the triangular-lattice antiferromagnet NdCd3P3

Abstract

We report a study of the magnetic ground state and crystal electric field (CEF) scheme in the triangular-lattice antiferromagnet NdCdP. Combined neutron scattering, magnetization, and heat capacity measurements demonstrate that the Nd moments occupying the triangular lattice in this material harbor hidden signs of frustration not detected in typical Curie-Weiss-based parameterization of the frustration index (). This is evidenced by a zero-field splitting of the Kramers' ground state and first excited state doublets at temperatures far in excess of as well as signatures of low-energy fluctuations for . A suppression of the zero-field ordered moment relative to its field saturation value is observed, and the impacts of this magnetic frustration as well as the coexisting bond frustration in the CdP honeycomb network on the physical properties of NdCdP are discussed.

Paper Structure

This paper contains 12 sections, 3 equations, 4 figures, 1 table.

Table of Contents

  1. Introduction
  2. Experimental Details
  3. Powder synthesis
  4. Magnetization and heat capacity measurements
  5. Neutron Scattering
  6. Results
  7. Magnetization
  8. Neutron diffraction
  9. Inelastic neutron scattering and crystal field analysis
  10. Heat capacity
  11. Discussion
  12. Conclusion

Figures (4)

  • Figure 1: (a) Field-dependent magnetization $M(H)$ at $T = 1.8$ K with spin-$\frac{1}{2}$ Brillouin + Van Vleck fit. (b) Scaled plot of $M$ vs $H/T$ after Van Vleck subtraction, showing agreement with $g_\mathrm{eff} = 1.86$.
  • Figure 2: (a) Neutron diffraction pattern at T = 0.07 K showing the overall Rietveld fit along with individual contributions from nuclear and magnetic Bragg peaks for NdCd$_3$P$_3$, as well as impurity nuclear and magnetic peaks from NdP. Magnetic peaks at $\mathbf{Q}$ = (0, 0, 1) and (0, 0, 2) are consistent with A-type antiferromagnetic order. (b) Crystal structure of NdCd$_3$P$_3$ with $\mathbf{k}$ = (0, 0, 0) antiferromagnetic order. (c) Top-down view of a triangular layer of Nd$^{3+}$ demonstrating ferromagnetic coupling of moments in-plane.
  • Figure 3: (a) Inelastic neutron scattering intensity $I(Q, \hbar\omega)$ at $T = 6$ K with $E_i = 55$ meV, showing CEF excitations of Nd$^{3+}$. (b) Momentum-integrated energy cut with CEF fit (solid line); inset: energy-level diagram of the five Kramers doublets. (c) High-resolution INS data with $E_i = 11$ meV resolving the first excited doublet. (d) Energy cut of the first excitation showing a $\Delta$E$_{split}$ = 0.8 meV splitting; solid line shows a model including a static molecular field of B$_\mathrm{eff}$ = 0.089(5) meV (root-mean-square magnitude determined from [0.11 (1), -0.11(1), 0.0] meV).
  • Figure 4: (a) Magnetic contribution to heat capacity C$_{p,\mathrm{mag}}$T$^{-1}$ from $\mu_0$H = 0 to 14 T, showing the suppression and broadening of the $T_N$ anomaly and a broad Schottky tail. (b) Fits to a two-level Schottky model of the Schottky tail at selected fields. (c) Extracted Schottky gap $\Delta$E$_\mathrm{Schottky}$ vs. applied field, showing linear Zeeman behavior with $g = 1.94(2)$.