Growth and characterization of Dy1-xYxMnO3 single crystals by optical floating zone technique: A combined X-ray diffraction and DC magnetization study

Large size single crystals of DyMnO3, YMnO3 and their solid solutions, Dy1-xYxMnO3, have been grown by the optical floating zone technique. It is shown that pristine DyMnO3 crystals grown in air atmosphere correspond to the orthorhombic phase in the Pnma space group symmetry while growth in the argon atmosphere leads to the hexagonal phase in the P63cm space group symmetry. The crystals grown in air atmosphere for the composition range 0.10 < x < 0.50 show coexistence of orthorhombic and hexagonal phases with increasing hexagonal phase fraction until at x - 0.60, the orthorhombic phase completely transforms to the hexagonal phase even in the air atmosphere. On the other hand, all the crystals grown in argon atmosphere correspond to the hexagonal phase only. Our Rietveld refinements using X-ray powder diffraction data on powders obtained after crushing the crystals further confirm the hexagonal structure in the P63cm space group symmetry for all crystals grown in argon atmosphere. The unit cell volume and the lattice parameters obtained by Rietveld refinement are shown to decrease with increasing Y3+ substitution at the Dy3+ site in DyMnO3. DC magnetisation measurements on h-Dy1xYxMnO3 single crystals reveal that Y3+ substitution marginally increases the antiferromagnetic ordering temperature (TN) from 67 K for h-DyMnO3 to 72 K for h-YMnO3. However, the first spin reorientation (SR) transition temperature (TSR1) of Mn3+ decreases with increasing Y3+ substitutions as per TSR1 - k(x-xc)0.3, where k is a proportionality constant and xc is the critical composition for which this transition temperature goes to 0 K. The remaining two magnetic transition temperatures related to Dy3+ reordering (rDy3+)/spin-glass transition (TSG) and second spin reorientation transition (TSR2) show very weak dependence on Y3+ substitution before going to 0 K around x = xc - 0.90 composition. A magnetic phase diagram of h-Dy1-xYxMnO3 showing stability field regions in respect of different magnetic phases is also presented.