Magnetic and Optical Properties of Ferrimagnets in the RbMgF3–RbCoF3 System

Abstract

Previously reported ABF3-type ferrimagnets with the hexagonal BaTiO3 structure all contain Ni++ as the predominate magnetic ion. This paper reports the discovery of new ferrimagnetic compositions in the RbMgF3–RbCoF3 system where Co++ is the only magnetic ion. Phase studies on this system show that at high temperatures the hexagonal phase is stable to about 70% RbCoF3. Single crystals were grown over this compositional range and their magnetic and optical properties studied. Compositions containing in excess of about 35% RbCoF3 are ferrimagnetic and their magnetic moments (as high as 22 emu/g) and Curie temperatures (up to 36°K) vary with Co++ concentration. The magnetization data are consistent with a model of a ⅓–⅔ ferrimagnetic spin arrangement. The B-B interaction, which is the resultant of the 90° Co++–F–Co++ and the direct Co++–Co+ interactions, appears to be strongly positive. Optical absorption data were used to determine the magnitude of the crystal field parameter Dq (870–880 cm−1) and the spin orbit interaction constant λ (190 cm−1). These data further indicate the strength of the crystalline field acting on the Co++ ion in the hexagonal structure, where ⅔ of the CoF6 octahedra share faces, is similar to that in ``cubic'' KCoF3 and RbCoF3 where they share corners.