Magnetic, thermal, and electronic-transport properties of EuMg2Bi2 single crystals
Abstract
The trigonal compound EuMg2Bi2 has recently been discussed in terms of its topological band properties. These are intertwined with its magnetic properties. Here detailed studies of the magnetic, thermal, and electronic-transport properties of EuMg2Bi2 single crystals are presented. The Eu+2 spins 7/2 in EuMg2Bi2 exhibit an antiferromagnetic (AFM) transition at a temperature TN=6.7 K, as previously reported. By analyzing the anisotropic magnetic susceptibility χ data below TN 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 a b -plane layers are aligned ferromagnetically in the a b plane with a turn angle between the moments in adjacent moment planes along the c axis of ≈120∘ . An alternate but less likely magnetic structure is a planar structure with nearest-neighbor Eu spins aligned at ≈120∘ with respect to each other, where these ordered-moment layers are stacked along the c axis. The magnetic heat capacity exhibits a λ anomaly at TN with evidence of dynamic short-range magnetic fluctuations both above and below TN. The high-T limit of the magnetic entropy is close to the theoretical value for spins 7/2. The in-plane electrical resistivity ρ (T ) data indicate metallic character with a mild and disorder-sensitive upturn below Tmin=23 K. An anomalous rapid drop in ρ (T ) on cooling below TN as found in zero field is replaced by a two-step decrease in magnetic fields. The ρ (T ) measurements also reveal an additional transition below TN 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 TN on the c -axis magnetic field H⊥ was derived from the field-dependent χ (T ) , Cp(T ) , and ρ (T ) measurements. This TN(H⊥) 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⊥-T plane.
- Publication:
-
Physical Review B
- Pub Date:
- June 2020
- DOI:
- 10.1103/PhysRevB.101.214407
- arXiv:
- arXiv:2004.03753
- Bibcode:
- 2020PhRvB.101u4407P
- Keywords:
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- Condensed Matter - Strongly Correlated Electrons;
- Condensed Matter - Materials Science
- E-Print:
- 15 pages, 16 captioned figures, 3 tables, 67 references. New figure and text added