Multiferroism in Fluorides

Despite several ferroelectric fluorides were reported as potential multiferroic systems, the coexistence of magnetism and ferroelectricity was experimentally proved only for the layered fluorides BaMF4 and in some terms of the large KxMF3 family, whose prototype is represented by K0.6FeF3 (or K3Fe5F15). The latter class of compounds is structurally related to the tetragonal tungsten bronzes (TTB), an important group of ferroelectric oxides, from which they can be ideally derived by the substitution of O by F, compensated by the replacement of high-valence with low-valence transition metals. This allows the setting of magnetic ordering which, together with the intrinsic ferroelectric character of the TTB structure, opens the route to multiferroicity. As a consequence, after some general studies published between the 1960s and 1980s, multiferroic fluorides were "rediscovered" in the last decade, according to the increasing interest in magnetoelectric systems, triggering a better definition of their interesting properties, which are resumed in this chapter.