  Materials science has been intensively developed during the last 30 years.
This is due, on the one hand, to an increasing demand of new materials for new
applications and, on the other hand, to technological progress which allows for
the synthesis of materials of desired characteristics and to investigate their
properties with sophisticated experimental apparatus. Among these advanced
materials, magnetic materials at nanometric scale such as ultra thin films or
ultra fine aggregates are no doubt among the most important for electronic
devices.In this review, we show advanced theoretical methods and solved
examples that help understand microscopic mechanisms leading to experimental
observations in magnetic thin films. Attention is paid to the case of
magnetically frustrated systems in which two or more magnetic interactions are
present and competing. The interplay between spin frustration and surface
effects is the origin of spectacular phenomena which often occur at boundaries
of phases with different symmetries: reentrance, disorder lines, coexistence of
order and disorder at equilibrium. These phenomena are shown and explained
using of some exact methods, the Green's function and Monte Carlo simulation.
We show in particular how to calculate surface spin-wave modes, surface
magnetization, surface reorientation transition and spin transport.
