Magnetic switching of Fe-porphyrin molecules adsorbed on surfaces: An XAFS and XMCD study.

Metalorganic molecules like Fe-porphyrin or haemoglobin have been investigated in great detail in the past. Its importance is obvious and has been measured mostly with molecules in random orientation. Here we report on experiments of a single monolayer of Fe-porphyrin in UHV aligned flat on ferromagnetic Ni and Co films. NEXAFS with linear and circular polarization is the spectroscopy of choice; it is elementspecific and measures the electronic structure as well as the magnetism at once. For the flat oriented monolayer of porphyrin molecules we have measured the angular dependence of XAFS at the C and N K-edge and XMCD at the Fe L-edges. The paramagnetic Fe-spin is aligned with respect to the ferromagnetic substrate. This can be parallel or antiparallel. Also nonmagnetic substrates like Cu (100) plus an external magnetic field will align the magnetic Fe-moment. This altogether opens a huge field for switching the 3d-spin from parallel to perpendicular of the molecular plane, which in turn willmodify the electronic transport properties and act as a single molecular switch.