Synthesis and Ferroelectric Field Effect Studies of Few-Layer CrCl₃

The van der Waals magnets CrX₃ (X = I, Br, and Cl) exhibit highly tunable magnetic properties and are promising candidates for developing novel two-dimensional (2D) spintronic applications. The ability to synthesize atomically thin CrX₃ samples and achieve voltage control of their magnetic states is critical for their technological implementation. In this talk, I’ll discuss our recent progress in the synthesis and ferroelectric field effect studies of large size few-layer CrCl₃ flakes. Using the physical vapor transport technique, we have deposited high-quality CrCl₃ flakes down to monolayer thickness on mica. Both isolated flakes with well-defined facets and long stripe samples exceeding 60 μm length have been obtained. High-resolution transmission electron microscopy and Raman studies confirm the high crystallinity of these samples. The tunneling magnetoresistance of graphite/CrCl₃/graphite tunnel junctions reveals in-plane magnetic anisotropy and Néel temperature of 17 K of CrCl₃. We encapsulate the tunnel junctions with free-standing ferroelectric PbZr_0.2Ti_0.8O₃ membranes and define the polarization state of the top-gate via conductive atomic force microscopy. Ferroelectric polarization reversal leads to nonvolatile modulation of the tunneling current, with an on/off ratio of 10⁶ obtained at room temperature. Compared with the negative tunneling magnetoresistance observed in hBN encapsulated devices, the PZT-gated CrCl₃ tunnel junctions exhibit positive tunneling magnetoresistance at low temperatures, suggesting a change of magnetic state. Our study provides an effective strategy to design low power, scalable, flexible 2D nanoelectronics and spintronics.<br/>This work was primarily supported by NSF through Grant No. DMR-2118828 and ERSCoR EQUATE Award No. OIA-2044049, and Nebraska Center for Energy Sciences Research.