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MA: Fachverband Magnetismus

MA 8: Spin-Dependent Phenomena in 2D (joint session MA/HL)

MA 8.1: Vortrag

Montag, 17. März 2025, 15:00–15:15, H19

Magnetoelectric behavior of breathing kagomé monolayers of Nb3(Cl,Br,I)8 from first-principles calculations — •John Mangeri — Technical University of Denmark, Kongens Lyngby, Denmark

We apply density functional theory to explore the magnetoelectric (ME) properties of two-dimensional Nb3(Cl,Br,I)8. These compounds have recently been proposed to exhibit coupled ferroelectric and ferromagnetic order leading to a switchable anomalous valley Hall effect (AVHE). Using both spin-spiral and self-consistent spin-orbit coupled calculations, we predict an in-plane 120 degree cycloid of trimerized spins as the ground state for Nb3Cl8. For Nb3Br8 and Nb3I8 we find long period incommensurate helical order. We calculate a number of magnetic properties such as the exchange constants, orbital magnetization, and Weiss temperatures. It is then shown that, despite having both broken inversion and time-reversal symmetry, the proposed AVHE and linear ME response are forbidden by the presence of helical order in the ground state. In addition, the computed switching trajectory demonstrates that it is unlikely that the polar state of the monolayers can be switched with a homogeneous electric field due to an unusual equation of state of the out-of-plane dipole moment. Nevertheless, we highlight that in the presence of a strong electric field, the trimerized spins in Nb3Cl8 will exhibit a magnetic phase transition from the 120 degree cycloid to out-of-plane ferromagnetic order, which restores the symmetry required for both AVHE and linear ME effects.

Keywords: magnetoelectrics; 2D materials; ferroelectric; magnetism