Krivnov, D. V. Dmitriev LOW-TEMPERATURE SUSCEPTIBILITY OF THE CLASSICAL FRUSTRATED FERROMAGNETIC SPIN CHAIN Abstract. <...> Low-dimensional magnets with competing (frustrated) interactions have attracted much attention last years because these systems have many unusual magnetic properties which are important for application. <...> One of the interest class of such compounds is cuprates consisting of edge-sharing chains with CuO4 plaquets with the ferromagnetic (F) and the antiferromagnetic (AF) exchange interactions between Cu2+ magnetic ions. <...> Of particular interest are the cuprates for which the frustration parameter is close to the critical value corresponding to the quantum phase transition. <...> A minimal model describing the magnetic properties of these cuprates is so-called F-AF chain with the F interaction of nearest-neighbor spins and the AF interaction of next-nearest-neighbor ones. <...> The aim of this work is to study lowtemperature magnetic properties of the F-AF chain with the frustration parameter which is close to the critical value. <...> We focus our attention on the behavior of the magnetic susceptibility and the correlation functions in this point. <...> The study of the low-temperature thermodynamics of the quantum F-AF chain is a complicated problem. <...> However, there are reasons to expect that the behavior of the low-temperature magnetic properties is universal for the quantum and the classical F-AF chains. <...> They are based on the transfer matrix method adapted to the systems with the competing interactions. <...> The partition function of the classical F-AF chain with the critical frustration parameter in the low-temperature limit can be reduced to the Schrodinger equation for the quantum particle in the special potential. <...> As a result we obtain exact low-temperature asymptotic of the pair correlation functions and the magnetic susceptibility. <...> In the T→0 limit the susceptibility diverges as T-4/3 and the correlation length as T-1/3. <...> So, the critical indices of the susceptibility and correlation length are 4/3 and 1/3 correspondingly. <...> The obtained results demonstrate strong influence of the frustration effects on the magnetic properties of the F-AF chain. <...> In particular, the critical index of the susceptibility is changed from 2 to 4/3 when the frustration parameter is changed from zero to the critical value and from 1 to 1.3 for the correlation length. <...> It is noted that the low-temperature asymptotic with the same critical indices have been obtained for the quantum F-AF chain by spin-wave method. <...> Key words: frustrated ferromagnetic chain, low-temperature susceptibility, lowdimensional magnet <...>