Open AccessThe decoherence of a central electron spin of an atom coupled to an anti-ferromagnetic spin bath in the presence of a time varying B-Field (VBF) is investigated applying the Holstein-Primak off and Bloch transformations approaches. The Boltzmann entropy and the specific heat capacity at a given temperature are obtained and show the correlation of the coupling of the spin bath and the electron spin of the central atom. At low frequencies the coherence of the coupled system is dominated by the magnetic field intensity. At low VBF intensity, there is decrease in entropy and heat capacity at increase external magnetic field that show the decoherence suppression of the central electron spin atom. The crossing observed in the specific heat capacity corresponds to the critical field point Bc of the system which represents the point of transition from the anti-ferromagnetic system to the ferromagnetic one.