  A model of magnetic phase transitions in plasmas is presented: plasma blobs
with pressure excess or defect are dia- or para-magnets and move radially under
the influence of the background plasma magnetisation. It is found that magnetic
phase separation could be the underlying mechanism of L to H transitions and
drive transport barrier formation. Magnetic phase separation and associated
pedestal build up, as described here, can be explained by the well known
interchange mechanism, now reinterpreted as a magnetisation interchange which
remains relevant even when stable or saturated. A testable necessary criterion
for the L to H transition is presented.
