2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/211845The spherical spin model with infinite-range ferromagnetic interactions is investigated analytically in the framework of non-extensive thermostatics generalizing the Boltzmann-Gibbs statistical mechanics. We show that for repulsive correlations, a new weak-ferromagnetic phase develops. There is a tricritical point separating para, weak-ferro and ferro regimes. The transition from paramagnetic to weak-ferromagnetic phase is an unusual first order phase transition in which a discontinuity of the averaged order parameter appears, even for finite number of spins. This result puts in a new way the question of the stability of critical phenomena with respect to the long-ranged correlations.4 pages, 3 figures, in the final form as in the journalStatistical MechanicsNuclear Theorytext