A complex magnetic structure of ultrathin Fe films on Rh (001) surfaces

► We studied structural and magnetic properties of Fe films grown on an Rh (001). ► MOKE measurements revealed that Fe films thicker than 2 ML are ferromagnetic at 5 K. ► Fe films with thickness of 2 ML & 3 ML exhibit out-of-plane magnetization, those thicker than 4 ML show in-plane magnetization. ► 1 ML Fe films have a complex magnetic configuration with zero net magnetization. ► A spin configuration model of 1 ML Fe is proposed based on an SP-STM observation.