  In previous studies, we have reported that double perovskite La2NiMnO6
presents a non-negligible potential for room temperature magnetocaloric tasks.
With the aim of improving even further the cooling performances and the working
temperature range of double perovskites, we report the magnetic and
magnetocaloric properties of La2MnFeO6 and ALaMnFeO6 (A = Sr, Ba, Ca)
compounds. X-ray diffraction (XRD) and Rietveld refinement show that La2MnFeO6
(LMFO) and CaLaMnFeO6 (CLMFO) samples crystallize in an orthorhombic structure
with the Pnma space group. However, a rhombohedral structure with the R3C space
group is obtained for BaLaMnFeO6 (BLMFO) and SrLaMnFeO6 (SLMFO) samples.
Substituting La by Ba or Sr in LMFO leads to a clear increase of the Curie
temperature (Tc) compared to LMFO from 150 K for BLMFO up to 350 K for SLMFO.
Moreover, CLMFO shows the smallest Tc down to 70 K. Ferromagnetic-like behavior
is observed for SLMFO and BLMFO while CLMFO's magnetism resembles that of LMFO.
A clear connection between the structural parameters and the magnetic
properties of these doped LMFO samples is unveiled as the highest Tc and the
largest magnetization are observed for SLMFO which shows also bond angles
closest to 180{\deg} and the smallest bond lengths, thus optimizing the
superexchange interaction. The partial substitution of Sr for La leads in fact
to a significant magnetocaloric effect over a wide operating temperature range
extending beyond 300 K. For some optimal growth conditions, its entropy change
varies slowly over an unusually large temperature range, which is of clear
interest from a practical point of view.
