  We report measurements of dm/dn in Si MOSFET, where m is the magnetization of
the two-dimensional electron gas and n is its density. We extended the density
range of measurements from well in the metallic to deep in the insulating
region. The paper discusses in detail the conditions under which this extension
is justified, as well as the corrections one should make to extract dm/dn
properly. At low temperatures, dm/dn was found to be strongly nonlinear already
in weak magnetic fields, on a scale much smaller than the characteristic
scales, expected for interacting two-dimensional electron gas. Surprisingly,
this nonlinear behavior exists both in the dielectric, and in the metallic
region. These observations, we believe, provide evidence for strong coupling of
the itinerant and localized electrons in Si-MOSFET.
