Ryszard Zdyb
Institute of Physics, Maria Curie-Sklodowska University, Lublin, Poland
What we can learn from the quantum size effect in ultrathin ferromagnetic films studied with Spin Polarized Low Energy Electron Microscopy

Spin Polarized Low Energy Electron Microscopy (SPLEEM) is a technique that allows investigation of the development of magnetism in low dimensional systems. Particularly, it is well suited for in situ studies of ultrathin ferromagnetic films. It gives possibility for the observation of onset of ferromagnetic order, the determination of magnetization direction and exchange asymmetry which can be considered as proportional to the magnitude of magnetization. In addition, SPLEEM gives possibility to correlate magnetic properties with the crystallographic structure and morphology of the investigated nanostructures via LEED and LEEM.
Beside above mentioned information SPLEEM/LEEM technique can deliver laterally resolved electron reflectivity vs energy of the incident electron beam spectroscopy data. It has been shown in a number of experiments that the reflectivity of low energy electrons from a layer with well-defined thickness reveals oscillations as a function of electron energy (quantum size effect). It appears that in a case of ferromagnetic layers the reflectivity is also spin-dependent. The energy position of the maxima and minima of the oscillations as well as their amplitude clearly depend on the direction of the polarization of the incident electron beam.
The observed spin-averaged and spin-resolved oscillatory changes of the reflectivity of low energy electrons can be used for the determination of the spin-averaged and spin-resolved, respectively, band structure of films above the vacuum level, inelastic mean free path and the phase shift of the electron wave at the film/vacuum and film/substrate interfaces. Moreover, the exchange asymmetry which also reveals oscillatory character caused by the quantum size effect can deliver additional information about the investigated ferromagnetic layer e.g. about its morphology and in more detail about its electronic structure.
As an example of application of SPLEEM in the studies of ferromagnetic nanostructures the system of ultrathin Fe films and islands grown on the W(110) surface under ultrahigh vacuum conditions will be discussed.