OBSERVATION BY SYNCHROTRON RADIATION TOPOGRAPHY OF THE PHASE COEXISTENCE AT THE TRIPLE POINT IN MNP

We have studied the coexistence of the helimagnetic, ferromagnetic and fan phases at, and around, the triple point, in two platelet-shaped c rystals of MnP when applying a magnetic field along the intermediate b axis. The 'real time' observation by synchrotron radiation topography using a video camera of the phase coexistence shows that the nucleati on of the third phase occurs at the interface which separates the two phases already present within the crystal, and that the interfaces bet ween the different phases have either very different shapes, or corres pond to a deformation which is not associated with a sharp image. We d iscuss these different features.