Frustrated Antiferromagnetic Spin 1/2 Double Chains with Ising-like Nearest-Neighbour Interactions

We examine double chains of spins 1/2 with Ising-like nearest-neighbor interactions showing magnetic frustrations that we define. The critical temperature of such systems is Tc = 0 K like for spin chains (1d systems). We recall the theoretical treatment which leads to the closed-form expression of the field-dependent partition function and the zero-field susceptibility. The study is restricted to low-temperature behaviors in the case of ferromagnetically coupled antiferromagnetic chains. We show that, if T > 0 K i.e., in the critical domain, for temperatures close to 0 K, the short-range order is conveniently described in the model of quasi-rigid quasi-independent blocks (the Kadanoff blocks) whose length is nothing but the correlation length of an isolated chain. This model, in particular, allows describing the experimental susceptibility of the compound VO(HPO4).H2O.