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

A systematic study of the microstructure and magnetocaloric effect in LaFe11.8Si1.2 and LaFe11.6Si1.4 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 LaFe11.8Si1.2 and 1323 K for LaFe11.6Si1.4. 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 ΔTad measurements were employed to directly assess the magnetocaloric effect. By application of a magnetic field of 1.9 T large ΔTad values of 7.3 K and 7.0 K in the vicinity of the transition temperatures were found for LaFe11.8Si1.2 and LaFe11.6Si1.4, respectively, after optimized annealing. By considering the partial irreversibility of magnetostructural transition the influence of thermal and magnetic hysteresis on magnetic entropy change and ΔTad is also discussed.

► Optimized annealing temperature and time in La-Fe-Si. ► Lamellar structure as an intermediate phase ► Large adiabatic temperature change of about 7 K for La-Fe-Si.