  We present a study of magnetic field fluctuations, in a slow solar wind
stream, close to ion scales, where an increase of the level of magnetic
compressibility is observed. Here, the nature of these compressive fluctuations
is found to be characterized by coherent structures. Although previous studies
have shown that current sheets can be considered as the principal cause of
intermittency at ion scales, here we show for the first time that, in the case
of the slow solar wind, a large variety of coherent structures contributes to
intermittency at proton scales, and current sheets are not the most common.
Specifically, we find compressive ($\delta b_{\|} \gg \delta b_{\perp}$),
linearly polarized structures in the form of magnetic holes, solitons and shock
waves. Examples of Alfv\'enic structures ($\delta b_{\perp} > \delta b_{\|}$)
are identified as current sheets and vortex-like structures. Some of these
vortices have $ \delta b_{\perp} \gg \delta b_{\|}$, as in the case of Alfv\'en
vortices, but the majority of them are characterized by $\delta b_{\perp}
\gtrsim \delta b_{\|}$. Thanks to multi-point measurements by Cluster
spacecraft, for about 100 structures, we could determine the normal, the
propagation velocity and the spatial scale along this normal. Independently of
the nature of the structures, the normal is always perpendicular to the local
magnetic field, meaning that $k_{\perp} \gg k_{\parallel}$. The spatial scales
of the studied structures are found to be between 2 and 8 times the proton
gyroradius. Most of them are simply convected by the wind, but 25\% propagate
in the plasma frame. Possible interpretations of the observed structures and
the connection with plasma heating are discussed.
