Theoretical justification of the magnetocaloric effect and spontaneous magnetization through critical behavior in Cd-doped MnCoGe alloy

Abstract A novel theoretical justification for determining the magnetocaloric effect and spontaneous magnetization of the MnCo 0.02 Cd 0.08 Ge alloy was investigated using Landau theory and the Arrott-Noakes equation. The critical exponents ( β and γ ) estimated from the modified Arrott plot method and the Kouvel-Fisher (KF) method are (0.337 and 1.169) and (0.336 and 1.170), respectively, suggesting a three-dimensional long-range magnetic coupling with the exchange distance decaying as J ( r )≈ r −4.83 . Additionally, the temperature-averaged entropy change (TEC) values under a 7 T magnetic field change are 5.40 J/(kg·K) and 4.31 J/(kg·K) for temperature ranges (Δ T H - C ) of 5 K and 25 K, respectively. Furthermore, two theoretical models based on Landau theory and the Arrott–Noakes equation, which incorporate Landau parameters and critical exponents, were employed to predict the magnetic entropy change (ΔS M ) in agreement with experimental results. Moreover, an effective novel method was proposed to define spontaneous magnetization through the relationship between −ΔS M and M, as well as the critical exponents.