Systematic study of the microstructure, entropy change and adiabatic temperature change in optimized La–Fe–Si alloys

Abstract A systematic study of the microstructure and magnetocaloric effect in LaFe 11.8 Si 1.2 and LaFe 11.6 Si 1.4 alloys over a large range of annealing temperatures and times has been carried out. With the aim of obtaining the pure 1:13 phase and maximum magnetic entropy change the annealing temperature was optimized at 1373 K for LaFe 11.8 Si 1.2 and 1323 K for LaFe 11.6 Si 1.4 . We found a unique morphology of eutectoid-type lamellae, which is suggested to be an intermediate phase upon formation of the 1:13 phase. Adiabatic temperature change Δ T ad measurements were employed to directly assess the magnetocaloric effect. By application of a magnetic field of 1.9 T large Δ T ad values of 7.3 K and 7.0 K in the vicinity of the transition temperatures were found for LaFe 11.8 Si 1.2 and LaFe 11.6 Si 1.4 , respectively, after optimized annealing. By considering the partial irreversibility of magnetostructural transition the influence of thermal and magnetic hysteresis on magnetic entropy change and Δ T ad is also discussed.