Direct magneto-optical observation of a structural phase transition in thin films of manganites

The spontaneous formation of twins in La2/3Ca1/3MnO3 films below T-S simila r to 105 K is observed by a magneto-optical technique. The twins are reveal ed as stripes along the {110} directions where magnetization tilts out of t he film plane due to the stresses in twins. Their appearance is associated with a martensitic phase transition in the film triggered by the cubic-to-t etragonal transition in the SrTiO3 substrate. It is found that magnetizatio n of the films proceeds by inhomogeneous rotation of magnetic moments. This is due to the presence of microscopic structural inhomogeneities. Their do minating role in the low-temperature transport can explain small effects of the transition at T-S on the resistivity.