Crystal structure and magnetic properties of some new hexagonal ferrites (Ba2Sn2MeFe10−xGaxO22) with the QS-structure

Ferrite Materials Containing Kagomé Layers: Chemistry of Ba2Fe11Ge2O22 and K2Co4V9O22 Hexaferrites

“…This is the case in Ba 2 Sn 2 Ga 3 ZnCr 7 O 22 , which was found to be highly frustrated, entering a spin-glass state at 1.5 K despite a Curie−Weiss theta value of −312 K. 27 The addition of magnetic ions to other sites reduces the symmetry and relieves this frustration, which results in magnetic ordering at high temperatures. For example, the series Ba 2 Sn 2 MFe 10−x Ga x O 22 (M = Mg, Ni, Co, Cu) were found to order ferrimagnetically with ordering temperatures between 334 and 444 K. 29 In these compounds, magnetic ions predominantly or fully occupy both tetrahedral sites and the Oh2 and Oh3 sites which leads to the ferrimagnetic interaction. The nonmagnetic Sn occupies the Oh1 site, and in some cases a small percentage of magnetic ion is also mixed onto this site.…”

“…33 Indeed, upon reconciling the structure of greenwoodite, Bartholomew and transition metal) and Ba 2 Sn 2 MFe 10 O 22 as being analogous to the mineral. 28,29,33 The interest in ferrite materials led us to seek a further simplified isostructural compound, Ba 2 Fe 11 Ge 2 O 22 , consisting of an electronically silent germanate oxyanion ((GeO 4 ) 4− ) with a single transition metal, iron, occupying all the transition metal sites. This represents a straightforward composition and distribution of elements, where Fe 3+ occupies all of the octahedral sites (Oh1, Oh2, Oh3), Fe 2+/3+ occupies the transition metal tetrahedral site (Td1), and the nonmagnetic Ge 4+ comprises the other tetrahedral oxyanion site (Td2).…”

“…In earlier work similar structures have been obtained using significant amounts of Sn at the octahedral site occupied by Fe1 in the case of Ba 2 Fe 11 Ge 2 O 22 , such as in Ba 2 Sn 2 MFe 10 O 22 (M = Mg, Mn, Ni, Co, Cu, Zn, Cd). 28,29,58,59 The presence of tetravalent Sn 4+ leads to the introduction of a wide range of divalent metals listed above. These are present in varying degrees in both tetrahedral and octahedral sites, including those in the spinel block.…”

“…27 An interesting series of studies were performed on some tin containing compounds of the QS phase, but the high temperature synthetic procedure and the demands of tin to be tetravalent and exclusively octahedral invariably led to mixed phases or disordered species, further complicating an already complex situation. 28,29 It should be noted that although the prototype M-hexaferrite BaFe 12 O 19 can be grown as single crystals relatively straightforwardly, 30 most of the other hexaferrites, including the Y-phase, have only been synthesized and studied as powders or nanocrystallites. 31,32 The Y (or QS) type materials also have a fascinating class of mineral analogues known as the greenwoodites.…”

“…These layers thus contain the appropriate symmetry for frustrated magnetism and possibly quantum spin behavior. − As with the layered perovskite derivatives, the hexagonal layers in the Y-type materials are separated by M 2+ –O salt-like strata, creating structures with frustrated two-dimensional (2-D) magnetic layers that are only weakly coupled to other magnetically ordered layers . An interesting series of studies were performed on some tin containing compounds of the QS phase, but the high temperature synthetic procedure and the demands of tin to be tetravalent and exclusively octahedral invariably led to mixed phases or disordered species, further complicating an already complex situation. , It should be noted that although the prototype M-hexaferrite BaFe 12 O 19 can be grown as single crystals relatively straightforwardly, most of the other hexaferrites, including the Y-phase, have only been synthesized and studied as powders or nanocrystallites. , …”