Fe(xML)/Au(xML) superlattices (1 ≤ x ≤ 4, ML: monatomic layer thickness) have been investigated by the ferromagnetic resonance method at room temperature. It has been confirmed that out-of-plane anisotropy field Hu shows oscillatory behavior as a function of Fe layer thickness with a period of 1 ML as reported previously from magnetization measurements. In addition, we have found that the in-plane fourfold anisotropy field H2 oscillates in a similar manner. The easy magnetization axis for x ≥ 2.25 is Fe [1 1 0] in contrast with the case of bulk Fe, and the values of H2 show maxima for x = 2.5 and 3.5, suggesting that the atomic steps at interfaces are formed along the Fe [1 1 0] direction. Furthermore, the interface roughness for x = non-integer causes wide distributions of Hu and H2 compared to those for x = integer with flat interfaces.
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