  The structural, magnetic, and magnetocaloric properties of epitaxial
Ni-Co-Mn-Al thin films with different compositions have been studied. The films
were deposited on MgO(001) substrates by co-sputtering on heated substrates.
All films show a martensitic transformation, where the transformation
temperatures are strongly dependent on the composition. The structure of the
martensite phase is shown to be 14M. The metamagnetic martensitic
transformation occurs from strongly ferromagnetic austenite to weakly magnetic
martensite. The structural properties of the films were investigated by atomic
force microscopy and temperature dependent X-ray diffraction. Magnetic and
magnetocaloric properties were analyzed using temperature dependent and
isothermal magnetization measurements. We find that
Ni$_{41}$Co$_{10.4}$Mn$_{34.8}$Al$_{13.8}$ films show giant inverse
magnetocaloric effects with magnetic entropy change of
17.5\,J\,kg$^{-1}$K$^{-1}$ for $\mu_0 \Delta H=5\,\text{T}$.
