Optical floating zone crystal growth and magnetic properties of MgCr ₂O₄

Large, high-quality single crystals of the magnesium chromate spinel, MgCr₂O₄, have been grown by the optical floating zone technique. The impact of experimental parameters including the feed rod density, growth atmosphere, temperature gradient, and the growth rate on eventual crystal quality have been studied. The best single crystals were obtained by growing in purified argon, at high growth rates of 8-24 mm/h and using a slow cooling procedure. The crystals were characterized using Laue and powder X-ray diffraction, energy dispersive X-ray analysis, and magnetization measurements. Lattice parameter measurements taken from the crystals prepared at various growth conditions combined with the magnetic data show that off-stoichiometric crystals have larger lattice constants and a higher magnetic susceptibility at T_N. Our results demonstrate the importance of correlating growth conditions with structural and physical properties to produce high quality single crystals that have physical properties commensurate with stoichiometric powder samples.