  We study coherent enhancement of neutrino electro-magnetic conversion in
crystals. Large coherency length which grows with the neutrino energy makes the
coherent enhancement particularly effective for very small masses. We derive
constraints on the conversion rate which follow from the Fresnel effects in
scattering of neutrinos on atomic chains. We comment on possible applications
of the crystal converter to searches for non-diagonal neutrino magnetic
transitions in the CERN neutrino beam.
