  During the study of magnetoresistivity in La(1-x)Ca(x)MnO(3) it was found
that after cycling of the magnetic field, some kind of magnetic field memory
effect was observed. For La0.5Ca0.5MnO3 after cycling of the magnetic field to
13T and back to zero, "frozen" magnetoresistivity decreases about 20 times
comparing to zero field value, while for La(0.47)Ca(0.53)MnO(3) it is already
about four orders of magnitude. This effect can be observed only for
concentration region 0.45 < x < 0.55. In zero magnetic field, temperature
dependence of resistivity ro(T) shows semiconducting-like behavior, while after
magnetic field cycling it becomes metal-like. So it looks as we are dealing
with magnetic field induced semiconductor (or dielectric) to metal transition.
Such effect can be explained within phase-separation picture. In zero magnetic
field material consists of antiferromagnetic matrix (insulating phase) and
coexisting ferromagnetic, conducting phase. Magnetic field application causes
ferromagnetic phase to form some kind of conducting channels which shunts
semiconducting matrix phase. Such structure is preserved after reduction of
magnetic field, leaving the material conducting.
