High-Efficiency Nonrelativistic Charge-Spin Conversion in X-Type Antiferromagnets

Abstract

Antiferromagnetic materials with spin splitting have attracted considerable attention for their symmetry-enabled anisotropic spin textures that sustain a zero net magnetization, thereby facilitating efficient spin-current generation. In this work, the highly efficient generation of nonrelativistic spin currents is demonstrated to be facilitated by the distinctive Fermi surface geometry of X-type collinear antiferromagnets. As a prototype conducting X-type antiferromagnet, the Fermi surface of $β-\mathrm{Fe}_2\mathrm{PO}_5$ exhibits a distinct $d$-wave altermagnetic characteristic, which compresses into a nearly X-shaped configuration. This results in highly efficient spin currents, achieving a charge-spin conversion efficiency of up to 90%. Moreover, the spin current polarization is controlled by the orientation of the Néel vector. When the Néel vector tilts to the out-of-plane direction, an in-plane injected charge current can generate a special spin current component with both spin polarization and propagation along the out-of-plane direction, whose charge-spin conversion efficiency substantially exceeds that of known ferromagnets, altermagnets, noncollinear antiferromagnets, and low-symmetry materials. The highly efficient charge-spin conversion in X-type antiferromagnets provides a novel and highly effective spin source system for the development of low-power spintronic devices.

Figures (5)

• Figure 1: Schematic illustration of anisotropic Fermi surface splitting induced by X-type collinear antiferromagnetic order. (a) Fermi surface structure in equilibrium, showing orthogonal spin-up (red) and spin-down (blue) contours. (b) Under an electric field $E\parallel[100]$, a transverse charge current forms for spin-up carriers, while spin-down carriers remain immobile. (c) Evolution of Fermi surface splitting under $E\parallel[110]$. (d) Charge currents for spin-up and spin-down carriers become equal in magnitude but perpendicular in direction under $E\parallel[110]$, generating a transverse spin current.
• Figure 2: Electronic structure of X-type antiferromagnetic $\beta$-Fe2PO5. (a) Crystal structure; (b) Brillouin zone with high-symmetry points labeled; (c) Electronic band structure with an enlarged view near the $E_{\rm F}$. Spin-resolved Fermi surfaces on the (d) (001)- and (e) (110)-oriented unit cells, with red and blue contours representing spin-up and spin-down channels, respectively.
• Figure 3: Spin-resolved Fermi surface projections. Projections on the $k_z = 0$ plane for (a) $\beta$-Fe2PO5 in the (001)-oriented unit cell and (b) $\beta$-Fe2PO5 in the (110)-oriented unit cell. Projections on the $k_z = \pi/2c$ plane for (c) RuO2 in the (001)-oriented unit cell and (d) RuO2 in the (110)-oriented unit cell. Red and blue contours represent spin-up and spin-down states, respectively.
• Figure 4: Charge-spin conversion response of $\beta$-Fe2PO5 as a function of scattering rate $\Gamma$. (a) For the (001)-oriented unit cell: $\cal T$-odd spin conductivity $|\sigma_{xx}^{z\rm ,odd}|$ (solid red), charge conductivity $\sigma_{xx}$ (dashed red), and charge-spin conversion efficiency $|\sigma_{xx}^{z\rm ,odd}/\sigma_{xx}|$ (solid blue). (b) For the (110)-oriented unit cell: corresponding $\cal T$-odd spin conductivity $|\sigma_{yx}^{z\rm ,odd}|$, conductivities $\sigma_{xx}$, and conversion efficiency $|\sigma_{yx}^{z\rm ,odd}/\sigma_{xx}|$. Schematic three-dimensional diagrams (top) illustrate the Néel vector $\hat{N}$ (purple double arrow), charge current $J$ (red arrow), spin polarization direction (green arrow), and spin current flow (black arrow).
• Figure 5: (a) The $\beta$-Fe2PO5 of (101)-oriented unit cell: corresponding $\cal T$-odd spin conductivity $|\sigma_{zx}^{z\rm ,odd}|$, conductivities $\sigma_{xx}$ and conversion efficiency $|\sigma_{zx}^{z\rm ,odd}/\sigma_{xx}|$. Schematic three-dimensional diagrams illustrate the Néel vector $\hat{N}$ (purple double arrow), charge current $J$ (red arrow), spin polarization direction (green arrow), and spin current flow (black arrow). (b) Spin Hall angles for Mn3Pt, Mn3Sn, MoTe2, WTe2, FePt, CoPt, RuO2, and $\beta$-Fe2PO5 with out-of-plane polarized spin currents. The bars filled with diagonal lines are obtained from calculations, while those without diagonal lines are obtained from experiments.