Enhancement of Interlayer Exchange in an Ultrathin Two-Dimensional Magnet

Abstract

Following 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].