Tunning magnetism and anisotropy by ferroelectric polarization in 2D van der Waals multiferroic heterostructures

Since the successful exfoliation of two-dimensional (2D) magnetic CrI 3 film, an increasing interest of research is the 2D analog of fascinating physical property of 3D material, of which the most attractive for both fundamental research and practical applications is the achieving effective magnetoelectric coupling and manipulation in 2D van der Waals (vdW) multiferroic heterostructure (HS). Herein, we report the discovery of ferroelectrically tunable orbital reconstruction in α-RuCl 3 /CuInP 2 S 6 2D vdW HSs, enabling the remarkable transitions of magnetic ordering from proximate quantum spin-liquid state to ferromagnetic as well as the easy magnetization axis tuning from in-plane to out-of-plane direction. In addition, Monte Carlo simulation verified that, α-RuCl 3 would transform into a perpendicular ferromagnetic material with Curie temperature of 89 K when the ferroelectric polarization points to α-RuCl 3 . Furthermore, by analyzing the density of states and the d-orbital-resolved magnetocrystalline anisotropy energy (MAE) of Ru atoms based on the second-order perturbation theory we elucidate that the contribution to MAE from the spin-orbit coupling interaction between d orbitals of Ru atoms show a transition from positive to negative, and ultimately dominating the MAE variation from easy-plane to easy-axis magnetization upon the reversible FE polarization. Therefore, the CuInP 2 S 6 nonvolatile ferroelectric switching enables the nonvolatile electrical control of magnetic ordering and anisotropy. This work paves the way for exploring high-efficiency nanodevices and nonvolatile information storage based on the multiferroic 2D vdW HSs. The highlights of this work are: 1. Our α-RuCl 3 /CuInP 2 S 6 HS endows with highly tunable magnetic properties. α-RuCl 3 was tuned to ferromagnetic state from proximate quantum spin-liquid state that the ferromagnetic and antiferromagnetic phase are nearly degenerate by ferroelectric control of the next nearest neighbor exchange coupling. 2. The switching of polarization in CuInP 2 S 6 leads to Ru ion orbital reconfiguration and the switching of the easy axis of magnetization from in-plane to out-of-plan. This makes Ru ions exhibit large perpendicular magnetic anisotropy, which not only can effectively stabilize the long-range magnetic ordering, but also enable the 2D easy axis ferromagnetic α-RuCl 3 more advantageous in functionality for practical applications. 3. Monte Carlo simulation verified that the ferromagnetic Tc of α-RuCl 3 /CuInP 2 S 6 HS with upward polarized state is enhanced to 89 K, far exceeding CrI 3 (45 K) and free-standing α-RuCl 3 monolayer (17 K), which provides a promising platform for advance in low-dimensional magnetoelectric physics and spintronics applications.