Effective field theory investigation for a disordered Ising model in the description of amorphous magnetic systems

The thermodynamic properties and phase diagrams of amorphous magnetic systems described by a disordered Ising model with binary probability are examined using effective field theory (EFT). A ferromagnetic to paramagnetic (FM–PM) phase transition occurs at a critical temperature τc where the spin susceptibility reveals an acutely sharp peak. By adjusting a disordered probability p, and a fluctuation parameter Δ driving mixed ferromagnetic interactions, we successfully provide a phase diagram illustrating the dependence of the critical temperature τc on the disordered probability p with various fluctuation strength Δ. The experimentally observed linear behavior of the τc−p curve is comprehensively explained in the weak disordered regime. Under an external field, we also examine the magnetocaloric effect by observing the magnetic entropy change (MEC) greatly enhanced in the strongly disordered regime where p≤0.3 and Δ>0.4. The linear behavior breaking of the maximal MEC on the fluctuation surprisingly agrees with experimental observations. •Thermodynamic properties of disordered Ising models with a binary probability.•Temperature dependence of thermodynamic quantities with probabilities and fluctuation.•Critical temperature dependence on probability and fluctuation without fields.•Maximal magnetic entropy change (MEC) ΔSM near τc with external fields.•An inverse relation between the maximal MEC and the critical temperature.