Preferred Orientation of Rare Earth (RE)-Doped Alumina Crystallites by an Applied Magnetic Field

Abstract : Alumina (aluminum oxide, Al2O3) has many favorable properties but is challenging to make transparent because of its anisotropic crystal structure. To combat the anisotropy, magnetic alignment of the particles can be used to minimize the change in index of refraction from grain to grain, thus reducing light scattering and allowing for transparency. Density functional theory results indicated that adding a rare-earth (RE) dopant enhanced the magnetic anisotropy of the alumina crystals, making them more responsive to a magnetic field. Further, different RE dopants were predicted to induce various degrees of magnetic moment localization and affect the orientation of the magnetic easy axis. It is of interest to investigate what effect the identity of the dopant has on the response to the magnetic field. RE dopants praesodymium, gadolinium (Gd), ytterbium (Yb), and erbium were used to dope nano-sized alumina powders, which were then suspended in epoxy resin that was allowed to cure within a magnetic field. The micro-texture of the aligned ceramic was analyzed by X-ray diffraction and the Lotgering factor calculated. Gd:Al2O3 was found to have approximately the same response as Yb:Al2O3 despite inducing different magnetic moments.