Magnetocaloric effect in potassium doped lanthanum manganite perovskites prepared by apyrophoric method

Abstract

The magnetocaloric effect (MCE) in fine grained perovskite manganites of the typeLa1−xKxMnO3 (0<x<0.15) prepared by a pyrophoric method has been investigated. Potassiumaddition in lanthanum manganite enhances the Curie temperature(TC) of the systemfrom 260.4 K (x = 0.05) to 309.7 K (x = 0.15). A large magnetic entropy change associated with the ferromagnetic–paramagnetictransition has been observed. The maximum entropy change|ΔSMMax| in an applied field of 1 T shows an enhancement by∼10% with increase inK content up to x = 0.15. La0.85K0.15MnO3 exhibitsthe largest |ΔSMMax| value of 3.00 J kg−1 K−1 at 310 K amongst the compounds investigated. Moreover, the maximum magnetic entropy changeexhibits a linear dependence with applied magnetic field. The estimated adiabatic temperature changeat TC and at 1 T field also increases with K doping, being a maximum of 2.1 K for theLa0.85K0.15MnO3 compound. The relative cooling power (RCP) ofLa1−xKxMnO3 compounds is estimated to be about one-third of that of theprototype magnetic refrigerant material (pure Gd). However,La1−xKxMnO3 compounds possess an MCE around room temperature, which is comparable to that of Gd. Further, tailoringof their TC, higher chemical stability, lower eddy current heating and lower cost of synthesis are someof the attractive features of K doped lanthanum manganites that are advantageous for amagnetic refrigerant. The temperature dependence of the magnetic entropy change(ΔSM) measured under various magnetic fields is explained fairly well using the Landau theoryof phase transitions. Contributions of magnetoelastic and electron interactionare found to have a strong influence in the magnetocaloric effect of manganites.