[en] We have studied the (001) surface of a Fe₃O₄ single crystal using low-energy electron diffraction (LEED), Auger electron spectroscopy (AES) and scanning tunneling microscopy (STM). The STM measurements were performed using a novel tip of antiferromagnetic MnNi alloy. Atomically resolved STM images provide evidence of a surface terminated at the octahedral plane, with rows of Fe cations running along the <110> crystallographic axes. Two different kinds of Fe cations with a separation of 6 Aa were imaged, while the periodicity between Fe cations of the same kind is about 12 Aa. We propose an interpretation of the anomalous corrugation observed in terms of a spin polarized effect, resulting in magnetic contrast between Fe²⁺ and Fe³⁺ ions in octahedral coordination