  The competition among different phases in perovskite manganites is pronounced
since their energies are very close under the interplay of charge, spin,
orbital and lattice degrees of freedom. To reveal the roles of underlying
interactions, many efforts have been devoted towards directly imaging phase
transitions at microscopic scales. Here we show images of the charge-ordered
insulator (COI) phase transition from a pure ferromagnetic metal with reducing
field or increasing temperature in a strained phase-separated manganite film,
using a home-built magnetic force microscope. Compared with the COI melting
transition, this reverse transition is sharp, cooperative and martensitic-like
with astonishingly unique yet diverse morphologies. The COI domains show
variable-dimensional growth at different temperatures and their distribution
can illustrate the delicate balance of the underlying interactions in
manganites. Our findings also display how phase domain engineering is possible
and how the phase competition can be tuned in a controllable manner.
