ID ferrimagnets

Special ID systems, chains made of rings, are fluorides with jarhte or usovite stmctures (Section 3.2.10). HomometaUic or bimetalhc chains with various combinations of spins (or nonmagnetic metals) allow the study of ID antiferromagnets, ID ferrimagnets, or hnear trimers. ... 

ID ferrimagnetic behaviour The interest for this new field is rapidly raising We report here some examples of EXAFS analysis about badly crystallized Cu—Ni, Cu—Zn and Cu—Mn oxalato derivatives and Cu—Mn dithiooxalato chains. 

The problem encountered here is rather different. The Cu(II)—Mn(II) dithiooxalato chain (CuMnDTO 7.5 H O) is obtained at room temperature under the form of single crystals and the structure of the pure product is fully characterized, without any disorder (Fig. 20). It is the first ID compound to present the ferrimagnetic behaviour shown in Fig. 21 curve 1. However, the partially dehydrated compound CuMn— (Cj0282)2 3 H2O, obtained at higher temperature, presents no longer ferrimagnetic properties (Fig. 21, curve 2) and its structure is not known. It exists intermediate hydrated materials where the magnetic properties are also very different from the fully hydrated material (Fig. 21, curve 3). 

In this section on the heterospin system, we will discuss three subjects 1) the magnetic coupling between the metal ion and organic spins through pyridine chromophores, 2) the photochemical formation of ferri- and ferrimagnetic chain (ID), and 3) the attempt to create frozen solution magnets (a carbene-based magnet). 

Fig. 3.9 Upper Antiferromagnetic coupling of two spins intermediated by a diamagnetic bridge (through-bond interactions). Middle After linking the units, a one-dimensional ferrimagnetic chain is obtained. Lower The ID chains are linked together through weaker intramolecular (through-space) interactions, indicated by dotted lines (for simplicity only two dimensions are shown)...

The material 3CuCl2.2dioxane consists of trimers of 5 = 1/2 spins, each with a spin of 3/2, weakly AFM coupled in ID. At low temperature it therefore approximates to an S = 3/2 AFM linear system. Measurements in fields up to 30 T, 780 GHz, showed the existence of three modes a mode (G) with an energy gap of 92 GHz, a paramagnetic branch (P) with g = 2.2 and no gap and a third ferrimagnetic mode (F) with high-field slope 2 r/3 at 1.6 K. The mode P was identified as the Zeeman transition between sublevels in S = 1/2 and 3/2 entities, the mode G as the direct excitation of the spin 1/2 entity and F the coupled mode of the stable S = 3/2 entity and the less stable S = 1/2 entity. The results differ from those observed for a real S = 3/2 chain due to the internal degrees of freedom of the 3/2 complex. 

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