Enhanced room-temperature magnetocaloric effect and tunable magnetic response in Ga-and Ge-substituted AlFe2B2

Abstract It is demonstrated that alloying additions of Ga and Ge enable tuning of the magnetocaloric response of the intermetallic boride AlFe2B2. Samples of nominal chemical composition Al1.2-xMxFe2B2 (M = Ga, Ge; x ≤ 0.30) were synthesized via suction casting (arc-melting and vacuum drawing into cylindrical copper molds) and subsequent heat treatment (annealed to 1373 K for 72 h). The saturation magnetization (Ms), Curie temperature (Tc) and specific heat capacity (Cp) of the samples all increase with increased Ga and/or Ge additions. Relative to the unmodified parent AlFe2B2 compound, a larger than two-fold improvement in the magnetic entropy change (ΔS (μ0Happ = 2 T) = 6.5 J kg−1K−1) and adiabatic temperature change (ΔTad (μ0Happ = 2 T) = 2.2 K) was observed at 305 K in a sample of composition Al1.1Ga0.05Ge0.05Fe2B2. The enhanced magnetocaloric response of the Al1.2-x(Ga,Ge)xFe2B2 system is ascribed to a complex amalgamation of chemical bonding and electronic effects that arise due to Fe and Al antisite defects within the AlFe2B2 lattice. Overall, these results provide insight of both fundamental and applied relevance concerning pathways for maximizing the magnetocaloric potential of AlFe2B2 for potential energy-related applications near room temperature.