Antisite disorder is a crystallographic defect that normally disrupts lattice continuity and dilutes magnetism. However, in some rare cases, instead of being suppressed, the spin order is reconfigured by antisite disorder, the detailed process of which, as well as the microscopic mechanism for the presence of antisite disorder, remains elusive. Here, we address these issues by investigating a newly synthesized postspinel oxide ${\mathrm{CaZnFe}}_2{\mathrm{O}}_5$, prepared through a high-pressure and high-temperature approach. Combined neutron diffraction and bulk magnetization measurements reveal A-type magnetic order below $T_{\mathrm{N}}\approx 190$ K, accompanied by a small uniform spin canting, possibly triggered by Dzyaloshinskii–Moriya interactions. Meanwhile, neutron refinement reveals a pronounced $\mathrm{Z}{\mathrm{n}}^{2+}$ and $\mathrm{F}{\mathrm{e}}^{3+}$ antisite disorder by 1/3, which, corroborated by Heisenberg model simulations, reshapes the competing exchange interaction network, converting the otherwise incommensurate magnetic ground state into an A-type spin configuration. First-principles calculations yield a much smaller energy increase in ${\mathrm{CaZnFe}}_2{\mathrm{O}}_5$ (89 meV per formula unit, f.u.) than in ${\mathrm{CaCuFe}}_2{\mathrm{O}}_5$ (340 meV/f.u.) upon antisite defect, providing quantitative support for the role of the lack of a Jahn–Teller distortion in facilitating the pronounced Zn and Fe antisite disorder, which profoundly impacts the macroscopic magnetic properties by reconfiguring exchange pathways.

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• Jahn-Teller effect
• Magnetism
• Crystal structures
• Transition metal oxides
• Neutron diffraction