Magnetic, thermal, and electronic-transport properties of EuMg₂Bi₂ single crystals

Journal Article · Wed Jun 03 00:00:00 EDT 2020 · Physical Review B

DOI:https://doi.org/10.1103/PhysRevB.101.214407· OSTI ID:1631824

Pakhira, Santanu  ^[1]; Tanatar, M. A.  ^[2]; Johnston, D. C.  ^[2]

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1. Ames Lab., Ames, IA (United States)
2. Ames Lab., Ames, IA (United States); Iowa State Univ., Ames, IA (United States)

The trigonal compound ${\mathrm{EuMg}}_2{\mathrm{Bi}}_2$ has recently been discussed in terms of its topological band properties. These are intertwined with its magnetic properties. In this paper detailed studies of the magnetic, thermal, and electronic-transport properties of ${\mathrm{EuMg}}_2{\mathrm{Bi}}_2$ single crystals are presented. The ${\mathrm{Eu}}^{+2}$ spins 7/2 in ${\mathrm{EuMg}}_2{\mathrm{Bi}}_2$ exhibit an antiferromagnetic (AFM) transition at a temperature $T_{\mathrm{N}}=6.7$ K, as previously reported. By analyzing the anisotropic magnetic susceptibility $\chi$ data below $T_{\mathrm{N}}$ in terms of molecular-field theory (MFT), the AFM structure is inferred to be a $c$-axis helix, where the ordered moments in the hexagonal $ab$-plane layers are aligned ferromagnetically in the $ab$ plane with a turn angle between the moments in adjacent moment planes along the $c$ axis of $\approx {120}^{°}$. An alternate but less likely magnetic structure is a planar structure with nearest-neighbor Eu spins aligned at $\approx {120}^{°}$ with respect to each other, where these ordered-moment layers are stacked along the $c$ axis. The magnetic heat capacity exhibits a $\lambda$ anomaly at $T_{\mathrm{N}}$ with evidence of dynamic short-range magnetic fluctuations both above and below $T_{\mathrm{N}}$. The high- $T$ limit of the magnetic entropy is close to the theoretical value for spins 7/2. The in-plane electrical resistivity $\rho \left(T\right)$ data indicate metallic character with a mild and disorder-sensitive upturn below $T_{\min }=23$ K. An anomalous rapid drop in $\rho \left(T\right)$ on cooling below $T_{\mathrm{N}}$ as found in zero field is replaced by a two-step decrease in magnetic fields. The $\rho \left(T\right)$ measurements also reveal an additional transition below $T_{\mathrm{N}}$ in applied fields of unknown origin that is not observed in the other measurements and may be associated with an incommensurate to commensurate AFM transition. The dependence of $T_{\mathrm{N}}$ on the $c$-axis magnetic field $H_{\perp }$ was derived from the field-dependent $\chi \left(T\right)$, $C_{\mathrm{p}}\left(T\right)$, and $\rho \left(T\right)$ measurements. This $T_{\mathrm{N}}\left(H_{\perp }\right)$ was found to be consistent with the prediction of MFT for a $c$-axis helix with $S=7/2$ and was used to generate a phase diagram in the $H_{\perp }\text{–}T$ plane.

• Research Organization: Ames Lab., Ames, IA (United States); Iowa State Univ., Ames, IA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES). Materials Sciences & Engineering Division
• Grant/Contract Number: AC02-07CH11358
• OSTI ID: 1631824
• Report Number(s): IS-J-10,230; PRBMDO; TRN: US2201031
• Journal Information: Physical Review B, Vol. 101, Issue 21; ISSN 2469-9950
• Publisher: American Physical Society (APS)
• Country of Publication: United States
• Language: English

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