  The surface spin polarization in the epitaxial films of a prototype
manganite, La0.7Sr0.3MnO3, has been investigated by Scanning Tunneling
Spectroscopy with ferromagnetic SP tips at room temperature. The manganite
surface splits into ferromagnetic (FM) and paramagnetic(PM) regions
characterized by metallic and insulating like behavior respectively. Spin
polarized spectroscopy with Ni tips has been performed separately for the two
phases, and the results compared with standard W and Pt tips. While PM exhibits
featureless tunneling characteristics, the FM regions exhibit at room
temperature strongly nonlinear behavior with a band-gap like behavior. The spin
resolved density of states of the FM regions of the manganite has been
extracted by the deconvolution of the spectroscopic curves. It indicates very
high spin polarization (nearly halfmetallic behavior) with the spin down band
separated from Fermi level by 0.4 eV. This value corresponds exactly to the gap
value measured for the whole surface of this manganite at low temperatures.
Thus the surface of the La0.7Sr0.3MnO3 films maintain even at room temperature
nano- and micrometric islands of very high spin polarization, while the total
polarization is given by the coverage of the surface by FM regions. This result
is extremely important for spintronic applications of this material and
indicates possible roots for the realization of manganite nanosized devices
with extremely high spin polarization.
