Magnetic hysteresis loop of one monolayer of Co on Cu(100)

We give experimental evidence that long-range ferromagnetic order exists at finite temperatures, over a macroscopic size and in the absence of magnetic field for 1 monolayer of Co on Cu(100). The magnetization as a function of the applied magnetic field follows an hysteresis loop. At remanence (zero-applied magnetic field) the film is in a single-domain state. The magnetization reversal occurs by breaking down of the film into magnetic domains.