Ultrafast electrically controlled magnetism in charge-order-induced ferroelectric altermagnet

Abstract

The altermagnetism with antiparallel spin alignment exhibits anisotropic spin splitting and may possess an insulating state with a high Neel temperature, while the charge-order-induced ferroelectricity has ultrafast electric polarization switching. Considering that altermagnetism requires breaking space inversion,, the physical foundation for exploring ultrafast electrically controlled magnetism in altermagnetic ferroelectric materials is thus established. In this Letter, based on symmetry analysis and first-principles electronic structure calculations, we predict that LiV$_2$F$_6$ is a material that simultaneously hosts altermagnetism and charge-order-induced ferroelectricity. Since both the altermagnetism and ferroelectricity originate from charge order, LiV$_2$F$_6$ should exhibit strong magnetoelectric coupling. Our calculations indeed demonstrate that electric polarization reversal can induce band spin-polarization switching in LiV$_2$F$_6$. Moreover, time-dependent density functional theory calculations show that the electric polarization reversal in LiV$_2$F$_6$ occurs in 15 femtoseconds. Consequently, ultrafast electrically controlled magnetism can be realized in LiV$_2$F$_6$. Given that LiV$_2$F$_6$ has already been experimentally synthesized, our work provides a promising material platform for achieving ultrafast electrically controlled magnetism, which might have significant implications for the design of future electronic devices.

Figures (4)

• Figure 1: Schematic illustration of manipulating altermagnetism by reversing polarization with external electric field in charge-order-induced ferroelectrics. The red/blue ball represents the atom with $+n$/$+(n+1)$ valence. The green arrow represents the direction of electric polarization. The red/blue arrow represents spin up/down, respectively. The Fermi surfaces are also marked by red and blue for spin up and down.
• Figure 2: (a) Crystal structure of HSS LiV2F6 at room temperature. The green/orange/blue-gray ball represent Li/V/F atom, respectively. (b) Energies for different magnetic orders as a function of $U$ in HSS LiV2F6. The ground state energy is set as 0 with every $U$ value. (c-f) The magnetic orders of HSS LiV2F6 considered in this paper. The orange ball represents V^2.5+ ion. Nonmagnetic Li and F atoms are hidden for simplicity.
• Figure 3: (a) Energies for different magnetic orders as a function of $U$ in LSS LiV2F6. The ground state energy is set as 0 with every $U$ value. (b) The comparison of ground state energies of HSS and LSS structure as a function of $U$. (c-f) The magnetic orders of LSS LiV2F6 considered in this paper. The dark red/pink ball represents V^2+/V^3+ ion, respectively. Nonmagnetic Li and F atoms are hidden for simplicity.
• Figure 4: The result of switching ferroelectric polarization of LiV2F6. (a) The NEB-simulated energies in the process of switching polarization. The insets sketch initial, intermediate and final structures. The dark red/orange/pink ball represents V^2+/V^2.5+/V^3+, respectively. (b-c) Electronic band structures of initial and final structures. The top-right inset in (b) illustrates the first Brillouin zone and the high symmetric $\textbf{k}$-points. The other two bottom-right insets illustrate the charge and magnetic order of the initial and final structures, respectively. (d) The time evolution of charge on spin-up atoms V1 and V4 in the polarization switching. (e) The corresponding dynamics for spin-down atoms V2 and V3.