Magnetization measurements were performed on two sigma-phase samples of Fe(100-x)V(x) (x=35.5, 34.1) vs. temperature, T, and in DC magnetic field, of various amplitudes. Using three characteristic temperatures, magnetic phase diagrams in the H-T plane have been designed testifying to a re-entrant character of magnetism. The ground magnetic state, a spin glass (SG), was evidenced to be composed of two sub phases: one with a weak irreversibility and the other with a strong irreversibility. Two critical lines were reconstructed within the SG state. Both of them show a crossover from the Gabay-Toulouse behavior (low field) to a linear and/or quasi-Almeida-Touless behavior. A strong difference in the effect of the applied magnetic field on the SG phase in the two samples was revealed.
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