title: Magnetocaloric effect in potassium doped lanthanum manganite perovskites prepared by a pyrophoric method.
abstract: The magnetocaloric effect (MCE) in fine grained perovskite manganites of the type La(1-x)K(x)MnO(3) (0<x<0.15) prepared by a pyrophoric method has been investigated. Potassium addition in lanthanum manganite enhances the Curie temperature (T(C)) of the system from 260.4 K (x = 0.05) to 309.7 K (x = 0.15). A large magnetic entropy change associated with the ferromagnetic-paramagnetic transition has been observed. The maximum entropy change |ΔS(M)(Max)| in an applied field of 1 T shows an enhancement by ∼10% with increase in K content up to x = 0.15. La(0.85)K(0.15)MnO(3) exhibits the largest |ΔS(M)(Max)| value of 3.00 J kg(-1) K(-1) at 310 K amongst the compounds investigated. Moreover, the maximum magnetic entropy change exhibits a linear dependence with applied magnetic field. The estimated adiabatic temperature change at T(C) and at 1 T field also increases with K doping, being a maximum of 2.1 K for the La(0.85)K(0.15)MnO(3) compound. The relative cooling power (RCP) of La(1-x)K(x)MnO(3) compounds is estimated to be about one-third of that of the prototype magnetic refrigerant material (pure Gd). However, La(1-x)K(x)MnO(3) compounds possess an MCE around room temperature, which is comparable to that of Gd. Further, tailoring of their T(C), higher chemical stability, lower eddy current heating and lower cost of synthesis are some of the attractive features of K doped lanthanum manganites that are advantageous for a magnetic refrigerant. The temperature dependence of the magnetic entropy change (ΔS(M)) measured under various magnetic fields is explained fairly well using the Landau theory of phase transitions. Contributions of magnetoelastic and electron interaction are found to have a strong influence in the magnetocaloric effect of manganites.
authors.affiliation: Thermophysical Measurements Laboratory, Cryogenic Engineering Centre, Indian Institute of Technology, Kharagpur 721302, India.
authors.forename: Soma
authors.initials: S
authors.lastname: Das
authors.forename: T K
authors.initials: TK
authors.lastname: Dey