  A detailed reinvestigation of magnetization in La0.5Ca0.5MnO3 reveals that
although a field of H = 7 T applied at T = 5 K after zero field cooling is
insufficient to convert the low temperature charge ordered antiferromagnetic
phase into ferromagnetic, annealing in a magnetic field as small as H = 1 T
induces ferromagnetic clusters in the charge ordered matrix. The volume phase
fraction of the ferromagnetic clusters increases nearly linearly with the
annealing field until Han = 4 T and then changes dramatically from about 11 %
at 5 T to 60 % at Han = 7 T. This is analogous to the field-induced micro to
macro polar domains in relaxor ferroelectrics. It is suggested that charge
ordered clusters coexist with ferromagnetic phase above the Neel temperature
(TN) and these clusters which transform into ferromagnetic by external magnetic
fields are supercooled below TN. Our results will be relevant to the
observation of many orders of decrease in the resistivity found for H << HC,
where HC is the critical field for metamagnetic transition.
