Magnetic Analysis of Ultrathin Fe Films on W(011) with SFEMPA

An ultra-high vacuum Scanning Tunneling Microscope (STM) is converted into a lens-less low-energy Scanning Electron Microscope when the tip-target distance is some tens of nanometers and the tip acts as a source of field emitted electrons. This primary electron beam excites locally secondary electrons out of the sample. Those escaping the tip-target junction are analyzed according to their spin. We use this technology to measure the local magnetization versus applied magnetic field in ultrathin Fe films on W(011) at room temperature. The resulting hysteresis loop is square. The coercive field has its maximum strength between 2.2 monolayers (0.07 T) and 3 monolayers (0.025 T), being larger than 0.1 T at 2.7 monolayers and decreasing to 0.0075 T at 6 monolayers. Rotation of the magnetization, domain wall pinning at incomplete layers and lattice misfits within the Fe films are discussed as possible explanations of this “singular” behavior.