Incorporating magnetism into two dimensional (2D) van der Waals (VdW) heterostrutures is crucial for the development of functional electronic and magnetic devices. Here we show that Nb3X8 (X = Cl, Br) is a family of 2D layered trimerized kagom\'e magnets that are paramagnetic at high temperatures and undergo a first order phase transition on cooling to a singlet magnetic state. X-ray diffraction shows that a rearrangement of the VdW stacking accompanies the magnetic transition, with high and low temperature phases consistent with STEM images of the end members {\alpha}-Nb3Cl8 and \b{eta}-Nb3Br8. The temperature of this transition is systematically varied across the solid solution Nb3Cl8-xBrx (x = 0-8), with x = 6 having transitions near room temperature. The solid solution also varies the optical properties, which are further modulated by the phase transition. As such, they provide a platform on which to understand and exploit the interplay between dimensionality, magnetism, and optoelectronic behavior in VdW materials.
@article{arxiv.1907.10108,
title = {Tunable Magnetic Transition to a Singlet Ground State in a 2D Van der Waals Layered Trimerized Kagom\'e Magnet},
author = {Christopher M. Pasco and Ismail El Baggari and Elisabeth Bianco and Lena F. Kourkoutis and Tyrel M. McQueen},
journal= {arXiv preprint arXiv:1907.10108},
year = {2019}
}