Magnetic behaviour of dirty multiband superconductors near the upper critical field

Magnetic properties of dirty multiband superconductors near the upper critical field are studied. The parameter $\kappa_2$ characterizing magnetization slope is shown to have a significant temperature variation which is quite sensitive to the pairing interactions and relative strengths of intraband impurity scattering. In contrast to single-band superconductors the increase of $\kappa_2$ at low temperatures can be arbitrary large determined by the ratio of minimal and maximal diffusion coefficients in different bands. Temperature dependencies of $\kappa_2(T)$ in two-band MgB$_2$ and iron-based superconductors are shown to be much more sensitive to the multiband effects than the upper critical field $H_{c2}(T)$.