Klein, DahliaMacNeill, DavidSong, QianLarson, DanielFang, ShiangXu, MingyuRibeiro, R. A.Canfield, P. C.Kaxiras, EfthimiosComin, RiccardoJarillo-Herrero, Pablo2023-02-132019-09-16Klein, Dahlia R., David MacNeill, Qian Song, Daniel T. Larson, Shiang Fang, Mingyu Xu, R. A. Ribeiro, et al. 2019. “Enhancement of Interlayer Exchange in an Ultrathin Two-Dimensional Magnet.” Nature Physics 15 (12): 1255–60.1745-24731745-2481https://nrs.harvard.edu/URN-3:HUL.INSTREPOS:37374360Following the recent isolation of monolayer CrI3 [1], there has been a surge of new two-dimensional van der Waals magnetic materials [2-12], whose incorporation in van der Waals heterostructures offers a new platform for spintronics [5-9], proximity magnetism [13], and quantum spin liquids [14]. A primary question in this burgeoning field is how exfoliating crystals to the few-layer limit influences their magnetism. Studies on CrI3 have shown a different magnetic ground state for ultrathin exfoliated films [1,5,6] but the origin is not yet understood. Here, we use electron tunneling through few-layer crystals of the layered antiferromagnetic insulator CrCl3 to probe its magnetic order, finding a ten-fold enhancement in the interlayer exchange compared to bulk crystals. Moreover, temperature- and polarization-dependent Raman spectroscopy reveal that the crystallographic phase transition of bulk crystals does not occur in exfoliated films. This results in a different low temperature stacking order and, we hypothesize, increased interlayer exchange. Our study provides new insight into the connection between stacking order and interlayer interactions in novel two-dimensional magnets, which may be relevant for correlating stacking faults and mechanical deformations with the magnetic ground states of other more exotic layered magnets, such as RuCl3 [14].en-USGeneral Physics and AstronomyJournal Article2023-02-1310.1038/s41567-019-0651-0