Single crystal growth of the hexagonal manganites R MnO3 (R=rare earth) by the optical floating-zone method

We report a study on the crystal growth of the hexagonal manganites R MnO3 (R=Y, Lu, Ho, Er, and Tm) by using an optical floating-zone method. It was found that high-quality single crystals of R=Y, Lu, and Ho could be easily grown with essentially the same conditions as those reported in the literature, that is, with an atmosphere of normal pressure Ar and oxygen mixture and a growth rate of 2-4 mm/h. However, these conditions were not feasible for growing good crystals of R=Er and Tm. The chemical analysis indicated that it was due to an off-stoichiometric phenomenon in the formed single crystals. We used an effective and simple way to resolve this problem by adjusting the nominal compositions of the polycrystal feed rods to be 1-2% rare-earth excess. The structures and physical properties were characterized by X-ray diffraction, magnetic susceptibility, specific heat, resistivity, and dielectric constant measurements.