  Surface magnetic properties of perovskite manganites have been a recurrent
topic during last years since they play a major role in the implementation of
magnetoelectronic devices. Magneto-optical techniques, such as X-ray magnetic
circular dichroism, turn out to be a very efficient tool to study surface
magnetism due to their sensitivity to magnetic and chemical variations across
the sample depth. Nevertheless, the application of the sum rules for the
determination of the spin magnetic moment might lead to uncertainties as large
as 40% in case of Mn ions. To overcome this problem we present an alternative
approach consisting of using X-ray magnetic circular dichroism in reflection
geometry. Fit of the data by using a computer code based in a 4X4 matrix
formalism leads to realistic results. In particular, we show that surface and
interface roughness are of major relevance for a proper description of the
experimental data and a correct interpretation of the results. By using such an
approach we demonstrate the presence of a narrow surface region with strongly
depressed magnetic properties in La2/3Ca1/3MnO3 thin films.
