Two-dimensional (2D) nanosheet arrays with unidirectional orientations are of great significance for synthesizing wafer-scale single crystals. Although great efforts have been devoted, the growth of atomically thin magnetic nanosheet arrays and single crystals is still unaddressed. Here we design an interisland-distance-mediated chemical vapor deposition strategy to synthesize centimeter-scale atomically thin Fe₃O₄ arrays with unidirectional orientations on mica. The unidirectional alignment of nearly all the Fe₃O₄ nanosheets is driven by a dual-coupling-guided growth mechanism. The Fe₃O₄/mica interlayer interaction induces two preferred antiparallel orientations, whereas the interisland interaction of Fe₃O₄ breaks the energy degeneracy of antiparallel orientations. The room-temperature long-range ferrimagnetic order and thickness-tunable magnetic domain evolution are uncovered in atomically thin Fe₃O₄. This strategy to tune the orientations of nanosheets through the an interisland interaction can guide the synthesis of other 2D transition-metal oxides, thereby laying a solid foundation for future spintronic device applications at the integration level.