Current-induced CrI3 surface spin-flop transition probed by proximity magnetoresistance in Pt

By exploiting proximity coupling, we probe the spin state of the surface layers of CrI₃, a van der Waals magnetic semiconductor, by measuring the induced magnetoresistance (MR) of Pt in Pt/CrI₃ nano-devices. We fabricate the devices with clean and stable interfaces by placing freshly exfoliated CrI₃ flake atop pre-patterned thin Pt strip and encapsulating the Pt/CrI₃ heterostructure with hexagonal boron nitride (hBN) in a protected environment. In devices consisting of a wide range of CrI₃ thicknesses (30-150 nm), we observe that an abrupt upward jump in Pt MR emerge at a 2 T magnetic field applied perpendicularly to the layers when the current density exceeds 2.5 × 10¹⁰ A m^-2, followed by a gradual decrease over a range of 5 T. These distinct MR features suggest a spin-flop transition which reveals strong antiferromagnetic interlayer coupling in the surface layers of CrI₃. We study the current dependence by holding the Pt/CrI₃ sample at approximately the same temperature to exclude the joule heating effect, and find that the MR jump increases with the current density, indicating a spin current origin. This spin current effect provides a new route to control spin configurations in insulating antiferromagnets, which is potentially useful for spintronic applications.