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Quantum Hall effect in a bulk antiferromagnet EuMnBi2 with magnetically confined two-dimensional Dirac fermions: Associate Professor Shintaro Ishiwata, Department of Applied Physics.

For the innovation of spintronic technologies, Dirac materials, in which low-energy excitation is described as relativistic Dirac fermions, are one of the most promising systems because of the fascinating magnetotransport associated with extremely high mobility. To incorporate Dirac fermions into spintronic applications, their quantum transport phenomena are desired to be manipulated to a large extent by magnetic order in a solid. We report a bulk half-integer quantum Hall effect in a layered antiferromagnet EuMnBi2, in which field-controllable Eu magnetic order significantly suppresses the interlayer coupling between the Bi layers with Dirac fermions. In addition to the high mobility of more than 10,000 cm2/V s, Landau level splittings presumably due to the lifting of spin and valley degeneracy are noticeable even in a bulk magnet. These results will pave a route to the engineering of magnetically functionalized Dirac materials.



(A to D) Temperature dependence of magnetic and transport properties near the AFM transition temperature (TN) for EuMnBi2. (A) Magnetic susceptibility M/H for the field parallel to the c axis (H||c) at 0.1 T (blue) and 7 T (red). Open symbols are the data for the field perpendicular to the c axis (H⊥c) at 0.1 T. (B) Intensity of resonant magnetic reflection (0 0 11) at 6.975 keV at 0 T. The inset shows the profile of the (0 0 11) reflection along [001] at 6.975 keV (resonant) and 7.00 keV (nonresonant). In-plane resistivity ρxx (C) and interlayer resistivity ρzz (D) at 0 and 9 T (H||c). Schematic sample configuration for the resistivity measurement is shown in each panel. emu/mol, electromagnetic unit per mole; a.u., arbitrary unit. (E) Schematic illustration of the plausible magnetic structure for EuMnBi2 at zero field, together with the formal valence of each ion. The arrangement of the Mn sublattice is assumed to be the same as in SrMnBi2 (45). (F) Magnetic phase diagram for the Eu sublattice as functions of field (H||c) and temperature. PM and AFM denote the paramagnetic and antiferromagnetic states, respectively. Hf and Hc correspond to the transition fields to the spin-flop AFM and PM (forced ferromagnetic) phases, respectively. Black arrows are schematic illustration of the Eu moments sandwiching the Bi− layer. Note the Mn sublattice orders at ~315 K (>TN).


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