Sliding Ferroelectric Metal with Ferrimagnetism

Abstract

Two-dimensional (2D) sliding ferroelectric (FE) metals with ferrimagnetism represent a previously unexplored class of spintronic materials, featuring out-of-plane FE polarization, metallic conductivity, and a finite net magnetization, which together enable electrically tunable spintronic functionalities via FE switching. Here, based on antiferromagnetic (AFM) metallic bilayers, we propose a general strategy for constructing 2D sliding FE ferrimagnetic (FiM) metals that can achieve triply-coupled switching, in which the FE polarization, spin splitting, and net magnetization are reversed simultaneously through FE switching. As a prototypical realization, we design a bilayer sliding FE metal with FiM order, derived from monolayer Fe$_5$GeTe$_2$ -- a van der Waals metal with intrinsic ferromagnetic order close to room temperature. The system exhibits a FE transition from a nonpolar (NP) AFM phase to a FE FiM phase via interlayer sliding. The in-plane mirror symmetry breaking in FE metallic states lifts the nonrelativistic spin degeneracy that exists in the NP phase, leading to a sizable net magnetic moment. Furthermore, the interplay between metallicity, ferroelectricity, and ferrimagnetism gives rise to pronounced sign-reversible transport responses near the Fermi level, all of which can be electrically controlled by FE switching. Our results establish sliding FE metals with FiM as a promising platform for electrically reconfigurable, high-speed, and low-dissipation spintronic devices.

Figures (4)

• Figure 1: Sliding FE magnetic insulators/semiconductors versus metals.a Schematic illustration of the sliding FE transition from a NP AFM phase to a FE FiM phase. The red and blue arrows represent the atomic magnetic moments, respectively. The interlayer sliding breaks the spin group symmetry [$\mathcal{C}_{2}{\parallel}\mathcal{O}$] and induces a net magnetic moment and out-of-plane FE polarization, leading to a FE FiM phase. b Panels (i) and (ii) correspond to the insulating/semiconducting and metallic states, respectively. The red and blue shaded areas represent the spin-resolved DOS for the spin-down and spin-up channels, respectively. The net magnetization is given by the difference between $iDOS^\uparrow(E_F)$ and $iDOS^\downarrow(E_F)$.
• Figure 2: Sliding configurations and FE switching in Fe$_5$GeTe$_2$ bilayer.a Side views of Fe$_5$GeTe$_2$ bilayer with AB, AC, and BA stackings. The cyclic switching between three stackings can be achieved through the relative displacement vector $\bm{t}$ between layers. b Transition energy barriers in the FE switching path. c$P_z$ and $M_N$ as a function of the relative displacement vector $\bm{t}$.
• Figure 3: Electronic structures and magnetoelectric responses of Fe$_5$GeTe$_2$ bilayer.a-c Band structures and $iDOS$ of the AB, AC, and BA stackings. Red and blue denote spin-down and spin-up channels, respectively. d Spin-splitting maps (spin-up minus spin-down) of two selected bands crossing the Fermi energy for the AB and BA stackings. e, f Dependence of $M_N$ on the applied out-of-plane electric field and the interlayer distance variation $\sigma$ in the AB- and BA-stacked Fe$_5$GeTe$_2$ bilayers, respectively.
• Figure 4: Sign-reversible anomalous transport properties for Fe$_5$GeTe$_2$ bilayer.a Schematic illustration of sign reversal in the AHE and ANE across the FE transition. b Schematic illustration of sign reversal in the MO Kerr and Faraday rotation angles across the FE transition. c AHCs of the AB and BA stackings. d ANCs of the AB and BA stackings at different temperatures. Solid and dashed lines correspond to AB and BA stackings, respectively. e, f MO Kerr and Faraday rotation angles for the AB and BA stackings.