Magnetic properties of nanocomposites based on mesoporous silica SiO ₂ with embedded iron particles are studied by small angle polarized neutron scattering at temperatures from 8 to 300 K and magnetic fields from 1 to 350 mT. This mesoporous silica forms highly regular hexagonal structures of nanotubes. A diffraction peak in SANS at q_c = 1.55 nm^-1 is observed, corresponding to a hexagonal structure with periodicity a = 4.6 nm. The scattering of the pure matrix Si0₂ is well fitted by a sum of two contributions: Porod scattering from large particles (1/q⁴) plus the scattering on a regular structure of pores (diffraction peak). Additional scattering is observed from samples with iron in the pores. The latter is fitted as scattering from bunches of nanowires with an average radius of R _b = 4.68 nm and a spread of ΔR_b = 0.9 nm. The nuclear-magnetic interference in the scattering of polarized neutrons is studied. We observe no interference scattering on the periodic structure that would be consistent with a hexagonal structure of nanotubes/nanowires. Instead, appreciable interference scattering is detected which is directly related with bunches of nanowires created during crystallization. The temperature and magnetic field dependences of this interference scattering demonstrate a transition from superparamagnetic to dipole-glass state at T = 80 K caused by an interplay of magnetic field, dipole-dipole, and thermal interactions.