Tailoring B-Site Preferential Occupations for Tunable Magnetism in Spinel High-Entropy Oxides via Nonmagnetic Al ³⁺ Probe

The rich diversity of transition-metal pairs bridged by oxygen contributes to the fascinating magnetic behaviors in high-entropy oxides (HEOs), while the complex interplay between multisite lattice configurations, spin states, and magnetic exchange interactions remains yet to be explored. Here, we report the Al 3+ -driven octahedral site preferential occupations and tunable magnetic frustration in spinel-type [5M 1/(5+ x ) Al x /(5+ x ) ] 3 O 4 ( x = 0–5; M = Cr/Fe/Mn/Zn/Co) HEOs. Nonmagnetic Al 3+ preferentially occupies octahedral sites (P B ), which significantly distorts the lattice with expansion in tetrahedral sites while shrinkage in P B –O. This structural evolution enables tuning of magnetic properties, e.g ., competition between ferromagnetic and antiferromagnetic states, spin glass, and spin-flop frustration states. Alternating-current susceptibility presents apparent spin frustration that follows a critical slowing-down model, which is suppressed when the Al 3+ level is beyond x = 2 because of the weakly frozen and disordered magnetic moments. These findings bring insights into modulating magnetic exchange interactions within multiple structural complexities for designing HEOs with tunable magnetic properties.