Magnetic properties of model nanomagnets with macroscopic value of the ground state spin

The peculiarities of the energy spectra of one-dimensional frustrated spin system formed by three-site spin-1/2 fragments and bridging spins s֮ ≥ 1/2 have been studied. For isotropic antiferromagnetic system with dominant interactions between spins of three-site fragments, the existence of quantum phase transitions with the macroscopic change of the ground state spin has been found. For anisotropic analog of the above spin system with Ising coupling between three-site fragment and bridging spins, it is shown that in addition to quantum phase transitions this model also can demonstrate pseudophase transitions at nonzero temperatures.