Magneto-optics observation of spontaneous domain structure in ferromagnetic La_0.78Ca_0.22MnO₃ single crystal

Spontaneous ferromagnetic domains in lightly Ca-doped La _1-xCa_xMnO₃ single crystals have been visualized and investigated by means of the magneto-optical technique. In marked difference to the magnetic contrast structures associated with magneto-crystalline anisotropy, which appear only in applied magnetic field, spontaneous ferromagnetic domains show up at low temperatures below the Curie temperature in zero applied field and are characterized by oppositely oriented spontaneous magnetization in adjacent domains. Ferromagnetic domains seen in zero field cooled samples take the form of almost periodic, corrugated stripe-like structures. Application of even a very weak magnetic field during cooling through the magnetic ordering transition changes the stripe domain structures into a bubble domain system.