Lanthanides in the frame of Molecular Magnetism

Abstract

Abstract. Molecular magnetism is producing new types of materials which cover up to date aspects of basic science together with possible applications. This article highlights recent results from the point of view of lanthanides which are now intensively used to produce single molecule magnets, single chain and single ion magnets. After a short introduction reminding the main steps of development of molecular magnetism, the basic properties of lanthanides will be covered highlighting important features which are enhanced by the electronic structure of lanthanides, like spin frustration and chirality, anisotropy and non collinear axes in zero and one dimensional materials. A paragraph of conclusions will discuss what has been done and theperspectives to be expected. A Nano history of molecular magnetismMolecular magnetism is a relatively recent section of magnetism which evolved from magnetochemistry. Magnetochemistry is the use of magnetic measurements in order to obtain structural information. An example should explain. Nickel(II) has a configuration 3d 8 . A compound with four ligands can have either a tetrahedral or square planar coordination geometry. A ligand field description shows that the five degenerate d orbitals in cubic symmetry remove their degeneracy due to low symmetry effects. The tetrahedral field is weaker than the square planar and the latter forces the electron spins to pair, while the weak tetrahedral keeps two electrons unpaired. A simple magnetic measurement at room temperature decides about the coordination structure. In fact the tetrahedral nickel (II) complexes are paramagnetic and square planar are diamagnetic. A useful technique but nothing more.The change occurred from the 60s of last century when it was realized that molecular chemistry could yield new types of magnetic materials, following the same type of evolution which took place on conductors where the introduction of molecular techniques determined a technological breakthrough.The goal at the beginning was to design and synthesize high T organic ferromagnets, but the challenge appeared soon to be too difficult and in order to start from a less hard field the goal was broadened rapidly to molecular ferromagnets i.e. to materials which may contain metal ions together with organic molecules. The results were promising, teaching how to develop strategies to design and synthesize ferro-or ferri-magnetic coupled molecules. The result was the production of low dimensional magnets while 3D materials were more difficult and the number of molecular magnets working at room temperature did not exceed 2 [1-4]. The critical temperatures of pure organic ferromagnets are still in the 30 K range.Luckily in those years there was a keen interest among physicists towards low D magnets and the exotic molecular magnets attracted the interest of quite a few. The problem was the different languages of the two communities. Physicists for instance needed one-dimensional antiferro-magnets with S> ½ to test the Haldane theory, and the only systems they we...