Magnetic and structural properties of high relative cooling power (Fe₇₀Ni₃₀)₉₂Mn₈ magnetocaloric nanoparticles

Earth-abundant, low-cost, and rare earth free magnetocaloric nanomaterials have attracted considerable attention for affordable, 'green', energy-efficient thermal management applications. Hence, we investigated the magnetocaloric properties and critical behavior of (Fe₇₀Ni₃₀)₉₂Mn₈ alloy nanoparticles. A near room temperature magnetocaloric effect, with a high relative cooling power (RCP), was obtained by alloying FeNi with Mn and fcc (γ) phase stabilization. The Curie temperature (T_C) of the γ- phase was 40 K less than that of the T_C of the bcc (α) phase. For a field change of 5 T, the RCP for the α- and γ- phase was found to be 507 J kg^-1 and 466 J kg^-1, respectively; these values are higher than those for Gd nanoparticles. The RCP exhibited a power law relationship with magnetic field H. Critical exponents values of δ = 4.71, β = 0.319 and γ = 1.195 were obtained, close to those obtained from the short range order 3D-Heisenberg model. Our results demonstrate the feasibility of developing high RCP, low-cost, rare earth free magnetocaloric nanoparticles for near room temperature applications.