Single crystal growth of the hexagonal manganites $R$MnO$_3$ ($R$ = rare earth) by the optical floating-zone method

摘要

We report a study on the crystal growth of the hexagonal manganites$R$MnO$_3$ ($R$ = Y, Lu, Ho, Er, and Tm) by using an optical floating-zonemethod. It was found that high-quality single crystals of $R$ = Y, Lu, and Hocould be easily grown with essentially the same conditions as those reported inliterature, that is, with an atmosphere of normal pressure Ar and oxygenmixture and a growth rate of 2--4 mm/h. However, these conditions were notfeasible for growing good crystals of $R$ = Er and Tm. The chemical analysisindicated that it was due to an off-stoichiometric phenomenon in the formedsingle crystals. We used an effective and simple way to resolve this problem byadjusting the nominal compositions of the polycrystal feed rods to be 1--$2\%$rare-earth excess. The structures and physical properties were characterized byX-ray diffraction, magnetic susceptibility, specific heat, resistivity, anddielectric constant measurements.