MnBi2Te4 has attracted tremendous research interest recently as the first intrinsic antiferromagnetic (AF) topological insulator. It undergoes a long-range AF order at TN 24 K accompanied with a cusp-like anomaly in the metallic resistivity. Here, we studied the effect of hydrostatic pressure on its electrical transport properties up to 12.5 GPa by using a cubic anvil cell apparatus. We find that TN determined from the resistivity anomaly first increases slightly with pressure and then decreases until vanished completely at ~7 GPa. Intriguingly, its resistivity (T) is enhanced gradually by pressure, and evolves from metallic to activated behavior as the AF order is suppressed. From the Hall resistivity measurements, we confirm that the n-type carriers dominate the transport properties and the carrier density is raised by pressure. In addition, the critical magnetic field Hc1 ~3.3 T at 0 GPa for the spin-flop transition to the canted AF state is found to increase to ~ 5 T and 7.5 T at 1 and 3 GPa. Highpressure XRD evidenced no structural transition up to 12.8 GPa. Based on the Hall resistivity results and first-principles calculations, we proposed that the intralayer direct AF interactions are strengthened by pressure and the competition between AF and FM interactions not only prevents long-range magnetic order but also promotes charge carrier localizations through enhance magnetic fluctuations at high pressures.
We report a comprehensive investigation of Ln2NiIrO6 (Ln = La, Pr, Nd) using thermodynamic and transport properties, neutron powder diffraction, resonant inelastic x-ray scattering, and density functional theory (DFT) calculations to investigate the role of A-site cations on the magnetic interactions in this family of hybrid 3d-5d-4f compositions. Magnetic structure determination using neutron diffraction reveals antiferromagnetism for La2NiIrO6, a collinear ferrimagnetic Ni/Ir state that is driven to long range antiferromagnetism upon the onset of Nd ordering in Nd2NiIrO6, and a non-collinear ferrimagnetic Ni/Ir sublattice interpenetrated by a ferromagnetic Pr lattice for Pr2NiIrO6. For Pr2NiIrO6 heat capacity results reveal the presence of two independent magnetic sublattices and transport resistivity indicates insulating behavior and a conduction pathway that is thermally mediated. First principles DFT calculation elucidates the existence of the two independent magnetic sublattices within Pr2NiIrO6 and offers insight into the behavior in La2NiIrO6 and Nd2NiIrO6. Resonant inelastic x-ray scattering is consistent with spin-orbit coupling splitting the t2g manifold of octahedral Ir 4+ into a J eff = 1 2 and J eff = 3 2 state for all members of the series considered.
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