On Ferro- and Antiferro-Spin-Density Waves Describing the Incommensurate Magnetic Structure of NaYNiWO₆

The incommensurate magnetic structure (0.47, 0, 0.49) of NaYNiWO₆ exhibits unconventional spin-density waves (SDWs) along the [100] direction, in which up and down spins alternate in each half-wave. This is in contrast to conventional SDWs, in which only one type of spin is present in each half-wave. We probed the formation of these unconventional SDWs by evaluating the spin exchanges of NaYNiWO₆ based on density functional theory calculations and analyzing the nature of the spin frustration in NaYNiWO₆ and by noting that a SDW is a superposition of two cycloids of opposite chirality. The unconventional SDWs along the [100] direction originate from the spin-frustrated antiferromagnetic chains of Ni²⁺ ions along that direction, leading to conventional SDWs along the [101] direction and unconventional SDWs along the [001] direction.