We show that a superstructure of antiferromagnetically interacting Fe$^{3+}$ ($S=5/2$) ions in double perovskites AFe$_{1/2}$M$_{1/2}$O$_{3}$ exhibits a ferrimagnetic ordering below $T_{fe} approx 5.6J_1$ ($J_1/k_B sim 50$~K), which is close to room temperature. Small clusters of the same structure exhibit a superparamagnetic behavior at $T lesssim T_{fe}$. The possibility of formation of such clusters explains the room-temperature (superpara)magnetism in 3$d$-metal based oxides.
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