Magnetic ordering and switching of iron porphyrin molecules on a substrate

We have studied the structural ordering and the magnetic coupling of in-situ sublimated Fe-based porphyrin molecules on epitaxially grown Ni and Co films on Cu(100) by means of X-ray absorption spectroscopy and X-ray magnetic circular dichroism at third generation synchrotron radiation facilities, in an experimental study which is combined by density functional theory (DFT). We demonstrate the necessary sensitivity to probe the magnetic properties even for sub-monolayer porphyrin coverages. We show that due to 90 degree super-exchange interaction between Fe atoms in the molecules and atoms in the substrate (Co or Ni) the paramagnetic molecules can be made to order ferro magnetically and even have their magnetisation direction switched by a magnetisation reversal of the substrate. Theory is demonstrated to reproduce the experimental observations.