Hexagonal Perovskites and Related Systems

1 Strings of Increasing Size in the CsNiF3-CsCdF3 System 

In the case of hexagonal perovskite-like fluorides, only the 2H, 6H, 10H, 9R and 12R arrangements have been found so far [36-38]. Thus, the system CsNiF3-CsCdF3 shows, according to the Ni/Cd ratio, 6H, 10H or 12R polytype 

The magnetic properties of Cs4Ni3CdF12 (12R) and Cs5Ni4CdF15 (10H) were shown to agree with a model of exchange-coupled units, on a large temperature scale [3]. The interactions are well-described by the Heisenberg Hamiltonian 

Inelastic scattering of thermal neutrons provides an alternative way to determine the magnitude of the exchange couplings [41-43]. An example is given for Cs4Ni3CdF12 in Fig. 6. 

Returning now to the magnetic properties, the plot of /-T vs T (Figs. 7-8) reveals, at very low temperatures, the influence of intercluster interactions and zero-field splitting for Ni(II) ions. Due to this last effect, the system is then anisotropic, and the complete Hamiltonian must be written  

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