Direct and indirect measurement of the magnetocaloric effect in the La0.5Ca0.5−xPbxMnO3 (0 ≤ x ≤ 0.2) manganites

Abstract

The magnetocaloric properties in La0.5Ca0.5−xPbxMnO3 (0 ≤ x ≤ 0.2) manganites are considered by both direct and indirect measurement techniques. The ac susceptibility shows that the compounds with low Pb doping exhibit mixture of CE-type AFM ordering and FM phase, while at high Pb doping FM phase is dominated. For samples x = 0 and 0.05, the M-H curves at different temperatures exhibit the magnetization first increases and then decreases with decreasing temperature, indicating the growth of the AFM phase below TN. In the curves for samples x = 0.1 and 0.2, with decreasing temperature the magnetization increases and the FM phase is overcoming at low temperature. The magnetic entropy change (ΔSM) is enhanced continuously with increasing Pb concentration up to x = 0.1, then slightly decreases. The magnetocaloric effect in the vicinity of TC for x = 0.1 and 0.2 was investigated by the direct field-induced adiabatic temperature change (ΔTad). The results of the direct method show the absolute values of obtained ΔTad are almost the same for both samples (0.62 and 0.53 K under 1.96 T for x = 0.1 and 0.2, respectively). The outcomes demonstrate that doping by Pb is a promising material for the magnetic refrigeration.