LOW TEMPERATURE X-RAY CRYSTALLOGRAPHY OF MAGNETS IN LOW MAGNETIC FIELDS. V.A.Finkel, National Science Center, Kharkov Institute of Physics & Technology, Kharkov, UA 310108, Ukraine

The aim of this paper is the demonstration of the possibility of XRD investigation of some structural aspects of magnetic phase transitions and domain structure rearrangements in the temperature range of 80 - 300 K in a low magnetic field up to 1000 Oe. The model objects of the investigation were single crystals of the rare earth metals (REM) Dysprosium and Terbium. We have measured the lattice parameters and diffraction line intensities as functions of a magnitude and a direction of an external magnetic field H at a constant temperature or as functions of a temperature at a constant field. We have obtained some new results concerning the magnetic phase H-T diagrams and the evolution of the REM domain structure in the ferromagnetic state in a magnetic field in a wide temperature range. In particular, we discovered that the type of H-T diagrams of REM essentially depends on the vector H orientation concerning crystallographic axes. We determined the presence of regions of the magneto heterogeneous state "helical anti ferromagnetism-collinear ferromagnetism", the magnetic vortex state, and the magnetic fan state on the H-T diagrams of REM. Also we ascertained that at a temperature reduction and a magnetic field rise the main types of domain walls in a ferromagnetic state of Dy and Tb are 120 deg walls.