Complex spin dynamics induced metamagnetic phase transitions in Dirac semimetal EuAuBi

TL;DR

This work investigates EuAuBi, a Dirac semimetal with localized Eu moments, using neutron diffraction, magnetization, specific heat, and transport to map magnetic order and textures. First-principles calculations confirm a Dirac crossing near the Fermi level along $ ext{Γ}$–$A$. Zero-field neutron diffraction reveals a commensurate canted AFM ground state with $ extbf{k}=(1/3,0,0)$, while field- and temperature-dependent measurements uncover a field-induced non-trivial spin texture with a tilted magnetization plateau and slow relaxation, inferred from ac susceptibility and relaxation analyses. The authors construct a detailed magnetic phase diagram, relate transport anomalies to spin-texture scattering, and argue that EuAuBi hosts coexisting momentum-space and real-space Berry curvature, offering a platform to study their interplay in a quantum material.

Abstract

We report a comprehensive investigation of the physical properties of the Dirac semimetal compound EuAuBi single crystals, using neutron diffraction, magnetization, electrical transport, and specific heat measurements. EuAuBi crystallizes in a hexagonal structure with space group P63mc (No. 186). First-principles calculations using density functional theory characterize it as a Dirac semimetal, with a notable band-crossing in proximity to the Fermi level (EF ) along the Γ-A direction. The crystal exhibits three distinct magnetic phases at 4 K (TN1), 3.5 K (TN2), and 2.8 K (TN3)as observed from magnetic and specific heat measurements. However, zero-field neutron diffraction resolves only two magnetic phases: a commensurate antiferromagnetic phase and a canted antiferromagnetic phase. Field-dependent ac and dc magnetization measurements uncover field-induced non-trivial spin textures in the magnetic field range 1.5 to 3 T, manifested as a tilted plateau in the magnetization curves. The interplay between conduction carriers and these spin textures is further evidenced by unique features in the magnetic field-dependent longitudinal resistivity in the system. Finally, we present a comprehensive magnetic phase diagram of EuAuBi, highlighting diverse spin alignments present in the material. EuAuBi thus emerges as a rare material system in which both momentum-space and real-space Berry curvature effects may coexist, providing a unique opportunity to investigate their interplay.

Figures (11)

• Figure 1: (a) Atomic arrangement of the EuAuBi crystal structure with the top and side view. Blue, Yellow and Green atoms represent the Eu, Au, and Bi atoms respectively. (b) Laue diffraction pattern of EuAuBi single crystal. (c) Raw Laue diffraction pattern is superimposed over a simulated pattern. (c) $\theta$ - 2$\theta$ XRD of the EuAuBi crystal, reflecting the peak orientations as indexed with the (000l) planes. The inset shows the grown EuAuBi crystal with the directions defined. (d) The band structure of EuAuBi with and without SOC. The inset shows the Dirac point (DP) along the $\Gamma$-A direction.
• Figure 2: (a) Temperature dependent zero-field-cooling (ZFC) and field-cooling (FC) magnetization M(T) for B = 0.1 T applied field in the ab plane of crystal (B$\perp$c). Inset shows a zoomed-in picture from 2 - 10 K, which indicates three transitions present in the system at $T_{N1}$, $T_{N2}$, and $T_{N3}$ (b) Temperature-dependent inverse susceptibility (1/$\chi$) in the paramagnetic regime (overlaps for B$\parallel$c and B$\perp$c) follows the extended Curie-Weiss law. The inset shows the temperature dependence of susceptibility ($\chi$(T)). (c) Temperature-dependent specific heat (C$_p$(T)) at B = 0 T. Inset shows zoomed-in picture from 2 - 10 K showing three transition temperatures similar to M(T). (d) Temperature dependent longitudinal resistivity ($\rho_{xx}$(T)) for B = 0 T and current applied in the ab plane of the crystal (I$\parallel$ [10$\bar{1}$0]). A zoomed-in view of $\rho_{xx}$(T) around the transition ($T_{N1}$) is shown in the inset.
• Figure 3: PND patterns of EuAuBi collected at different temperatures along with Rietveld refinements: (a) 10 K (paramagnetic region), (b) 3.5 K, and (c) 1.5 K (below the long-range ordering temperature). The blue and black vertical ticks indicate the Bragg peak positions corresponding to the main EuAuBi phase and a trace amount of the binary AuEu impurity phase, respectively. The red ticks in (b) and (c) mark the positions of the magnetic Bragg reflections. The green line below the Bragg markers represents the difference between the experimental and calculated profiles. Panel (d) displays the temperature-dependent PND patterns in the 1.5–10 K range, illustrating the evolution of magnetic Bragg peaks below the ordering temperature. Panel (e) presents a perspective view of the refined Eu spin configuration at 1.5 K.
• Figure 4: (a) Isothermal field-dependent magnetization from 0 to 14 T dc magnetic field at T = 2 K for B$\parallel$c and B$\perp$c configuration. (b) Isothermal field-dependent magnetization at different temperatures with dc field from 0 - 7 T dc field for B$\perp$c configuration. (c) Zoomed-in view of (b), from 1.5 to 3.5 T, revealing the metamagnetic transitions. B$_1$ and B$_2$ are marked as the starting and ending of the hysteresis around 2 T, B$_3$ and B$_4$ are marked as the starting and ending of the hysteresis around 3 T. The arrow highlights the shift in hysteresis towards lower magnetic fields with increasing temperature. Temperature-dependent magnetization at different magnetic fields for field-cooled cooling (FCC) and field-cooled warming (FCW) curves shown in black and red colors, respectively for (d) B$\perp$c and (e) B$\parallel$c. T$_S$ denotes the middle of the thermal hysteresis for B$\geq$ 1.6 T and the arrow shows the shifting of hysteresis towards lower temperature as B increases.
• Figure 5: (a) Field-dependent real part of ac susceptibility ($\chi$$^\prime$(B)) for B$\perp$c at different temperatures. An ac field of 9 Oe with frequency 93 Hz, is superimposed over the varying dc field.(b) Field dependent dM/dB at different temperatures (as derived from M(B) in fig 4c). Comparison of dM/dB and $\chi$$^\prime$ at (c) T = 2 K, (d) T = 2.2 K, (e) T = 2.5 K, (f) T = 2.8 K, (g) T = 3 K, (h) T = 4 K.