A New Mixed-Valence Ferrite with a Cubic Structure, YBaFe₄O₇: Spin-Glass-Like Behavior

Abstract

A new mixed-valence ferrite, YBaFe 4 O 7, has been synthesized. Its unique cubic structure, with a = 8.9595(2) Å, is closely related to that of the hexagonal “114” oxides YBaCo 4 O 7 and CaBaFe 4 O 7 . It consists of corner-sharing FeO 4 tetrahedra, forming triangular and kagome layers parallel to (111) C . In fact, the YBaFe 4 O 7 and CaBaFe 4 O 7 structures can be described as two different “ ccc ” and “ chch ” close packings of [BaO 3 ] ∞ and [O 4 ] ∞ layers, respectively, whose tetrahedral cavities are occupied by Fe 2+ /Fe 3+ cations. The local structure of YBaFe 4 O 7 is characterized by a large amount of stacking faults originating from the presence of “hexagonal” layers in the “ ccc ” cubic close-packed YBaFe 4 O 7 structure. In this way, they belong to the large family of spinels and hexagonal ferrites studied for their magnetic properties. Differently from all the ferrites and especially from CaBaFe 4 O 7, which are ferrimagnetic, YBaFe 4 O 7 is an insulating spin glass with T g = 50 K.