Feature article. Organic-intercalated halogenochromates(II): low-dimensional magnets

Abstract

Ferromagnetism in non-metallic solids is quite a rare property. In solids containing molecular building blocks it is even rarer. One strategy for preparing ionic ferromagnets is to combine a low-dimensional continuous lattice containing transition-metal ions with organic molecular ions. In this article we review the synthesis, structures and magnetic and optical properties of halogenochromate(II) salts with substituted ammonium cations. The shape of the latter has a striking influence on the bulk magnetic behaviour of the solids. Monosubstituted cations yield tetrahalogenochromates(II) with layer structures which are ferromagnets with Curie temperatures up to 60 K. On the other hand, tetramethylammonium trihalogenochromates(II) are one-dimensional antiferromagnets. The striking difference in the intensities of the visible absorption spectra of the two classes of materials can be explained by an exchange-induced electric-dipole mechanism.