Nonlinear Hall Effect in Antiferromagnetic Half-Heusler Materials

It has recently been demonstrated that various topological states, including Dirac, Weyl, nodal-line, and triplepoint semimetal phases, can emerge in antiferromagnetic(AFM) half-Heusler compounds. However, how to determine the AFM structure and to distinguish different topological phases from transport behaviors remains unknown. We show that, due to the presence of combined time-reversal and fractional translation symmetry, the recently proposed second-order nonlinear Hall effect can be used to characterize different topological phases with various AFM configurations. Guided by the symmetry analysis, we obtain expressions of the Berry curvature dipole for different AFM configurations. Based on the effective model, we explicitly calculate the Berry curvature dipole, which is found to be vanishingly small for the triple-point semimetal phase, and large in the Weyl semimetal phase. Our results not only put forward an effective method for the identification of magnetic orders and topological phases in AFM half-Heusler materials, but also suggest these materials as a versatile platform for engineering the nonlinear Hall effect.

Chiral mesostructured hematite with temperature-independent magnetism due to spin confinement

Hematite(α-Fe_(2)O_(3))is known to undergo conversion from weak ferromagnetic to antiferromagnetic as the temperature decreases below the Morin temperature(TM=250 K)due to spin moment rotation occurring during the Morin transition(MT).Herein,we endowed hematite with mesostructured chirality to maintain weak ferromagnetism without MT.Chiral mesostructured hematite(CMH)nanoparticles were prepared by a hydrothermal method with glutamic acid(Glu)as the symmetry-breaking agent.The triangular bipyramidal CMH nanoparticles were composed of helically cleaved nanoflakes with twisted crystal lattice.Field-cooled(FC)magnetization measurements showed that the magnetic moments of CMH were stabilized without MT within the temperature range of 10–300 K.Hysteresis loop measurements confirmed the weak ferromagnetism of CMH.The enhanced Dzyaloshinskii–Moriya interaction(DMI)was speculated to be responsible for the temperature-independent weak ferromagnetism,in which the spin configuration would be confined with canted antiferromagnetic coupling due to the mesostructured chirality of CMH.