First-principles study on spin density wave in La₃Ni₂O7-δ

The recent discovery of high-temperature superconductivity in high-pressurized La₃Ni₂O7-δ has garnered significant attention. Using density functional theory, we investigate the magnetic properties of La₃Ni₂O₇ at ambient pressure. Our calculations suggest that with δ=0, the double spin stripe phase is favored as the magnetic ground state. Oxygen vacancies may effectively turn nearest Ni spins into charge sites. Consequently, with moderate δ values, our theoretical magnetic ground state exhibits characteristics of both double spin stripe and spin-charge stripe configurations, providing a natural explanation to reconcile the seemingly contradictory experimental findings that suggest both the configurations as candidates for the spin-density-wave phase. With higher δ values, we anticipate the ground state to become a spin-glass-like noncollinear magnetic phase with only short-range order. The oxygen vacancies are expected to significantly impact the magnetic excitations and the transition temperatures TSDW. We further offer a plausible explanation for the experimental observations that the measured TSDW appears insensitive to the variation of samples and the lack of direct evidence for long-range magnetic ordering.