Electrical switching of an unconventional odd-parity magnet

Magnetic states with zero magnetization but exhibiting non-relativistic spin splitting are exceptional candidates for next-generation spintronic devices. Several magnetic states with nontrivial spin textures have recently been discovered, including even-parity d, g, or i-wave altermagnets, as well as odd-parity p-wave magnets. Controlling the spin polarization of these magnetic states via voltage is of great interest for developing energy-efficient, compact devices for information storage and processing. Spin-spiral type-II multiferroics are ideal candidates for such voltage-based control, as their inversion-symmetry-breaking magnetic order induces ferroelectric polarization, enabling symmetry-protected cross-control between odd-parity spin polarization and ferroelectric polarization. In this work, we combine photocurrent measurements, first-principles calculations, and group-theory analysis to provide direct evidence that the spin polarization in the spin-spiral type-II multiferroic NiI2 exhibits odd-parity character linked to the ferroelectric polarization.