Spin-1/2 ladder compounds

Besides the electrical conductivity, a number of other applications of [M(dmit)2] have been investigated. For example, molecular-based magnets, such as the spin ladder compound p-EPYNN][Ni(dmit)2] [p-FFYNN]" " = p-N-ethylpyridinium a-nitronyl nitroxide) was reported in 1996. In the crystal, the radical cationic molecules, p-EPYNN, form one-dimensional chains with ferromagnetic interactions, while the chains of [Ni(dmit)2] monovalent anions, in a ladder formation, exhibit antiferromagnetic interactions. The magnetisation is explained by the sum of them. 

Recently, Larkin et al. (2000) have encountered (in a study of the spin-ladder system Sr(Cui xZnj )203, which falls outside this review, but see sect. 8.3.4) muon spin relaxation functions with too shallow and too broad minima of polarization to be reproduced by Kubo-Toyabe functions. Again, longitudinal field data showed the spin system to be static. These authors used an approach (called Kubo golden rule, KGR), which was originally derived by Kubo (see Kubo 1981 and Yamazaki 1997) to describe their findings. For details we refer to the original papers. The KGR method allows the calculation of the muon spin relaxation function for arbitrary field distributions (if they can be described by arithmetic function). In the spin-ladder compound an exponential field distribution reproduced the data. The approach of Noakes and Kalvius (1997) can be reproduced using KGR. 

A deeper analysis [80] on this Cu - Dy chain showed that NN and NNN interactions are efficient above Tc and that inter spin-ladder ferromagnetic interaction is observed in this family of compounds [79-82]. Attempts were made to use the 3d tectons with other lanthanide precursors, such as hexanuclear lanthanide clusters. Regular chains were obtained with Dy-Cu ferromagnetic interaction but their close packing prevents observation of SCM behaviour [83]. 

Although isostructural to the Au complex, the Ni and Pt salts do not form spin-ladder systems. This may be due to slight differences in the transfer integrals within the DT-TTF stacks and also to the paramagnetism of [M(mnt)2] (M = Ni, Pt) that may interact with the DT-TTF system. Related Co and Fe compounds have also been reported (311), but they are just simple ionic salts as shown by their 1 1 stoichiometry (instead of the 2 1 stoichiometry for the Au, Ni and Pt compounds). Very recently, Ribera et al. (307) published an excellent and detailed report on this family of compounds. 

In Section III, we also discussed the spin-ladder behavior of dithiolene complex-based compounds, namely, (p-EPYNN) Ni(dmit)2], (DT-TTF)2-[Au(mnt)2], and [Cp2M(dmid)](TCNQF4). All of these compounds display semiconducting behavior and no interplay of electrical and magnetic properties was reported. 

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