Single Crystal Growth of Yttrium Orthoferrite by a Seeded Bridgman Technique

Single crystals of yttrium orthoferrite (YFeO3) 15 mm in diameter and 28‐mm long have been grown from pure Y2O3–Fe2O3 melts contained in platinum crucibles. At the melting point of YFeO3, 1680±5°C, the equilibrium oxygen pressure over the Y2O3–Fe2O3 system is approximately one atmosphere, hence a modified Bridgman technique was used. A Pt‐40% Rh resistance furnace capable of continuous operation at 1750°C under one atmosphere of oxygen was provided with baffles to obtain the desired temperature profile. Supercooling of pure Y2O3–Fe2O3 melts was found to be excessive, ∼100°C, so the Bridgman‐type crucibles were modified to permit seeding. When growth rates were kept below 1.5 mm/h, crystals exhibiting coercivities as low as 0.009–0.012 Oe were obtained. Crystals grown at high rates or from off‐stoichiometry melts contained several types of defects. Precipitate‐bubble pairs, isolated bubbles, a‐b type twins, cracks and optical density variations have been observed. The origin of these defects and steps taken to eliminate them, as well as their effect on cylindrical domain propagation, are discussed.