Helimagnetism in the candidate ferroelectric CrI2

CrI2 is a van der Waals layered material that exhibits helimagnetism that propagates along ribbon chains. This is determined from neutron time-of-flight diffraction measurements. Below 𝑇𝑁=17 K in the orthorhombic structure, a screwlike helimagnetic order develops with an incommensurate wave vector of 𝐪≈(0.2492,0,0) at 8 K. Using density functional theory (DFT)+𝑈 calculations, the 𝐽1−𝐽2 model is leveraged to describe the helimagnetism, where 𝐽1⁡(>0) and 𝐽2⁡(<0) correspond, respectively, to a ferromagnetic nearest-neighbor and antiferromagnetic next-nearest-neighbor intrachain interaction. The DFT+𝑈 calculations suggest that orthorhombic CrI2 satisfies conditions that favor formation of helimagnetic order.