Structural, magnetic and magnetocaloric properties in La0.5-xRexCa0.5MnO3 manganites (x=0; 0.1 and Re = Gd, Eu and Dy)

Structural, magnetic and magnetocaloric properties of the compounds La0.5-xRexCa0.5MnO3 (x = 0; 0.1 and Re = Gd, Eu and Dy) powder samples have been investigated. All our samples were synthesized using the solid state reaction at high temperature. All the samples are single phase and crystallize with Pnma space group. Magnetization measurements versus temperature in a magnetic applied field of 0.05 T show that all our substituted La0.4Re0.1Ca0.5MnO3 (Re = Gd, Eu and Dy) samples exhibit a paramagnetic (PM) to ferromagnetic (FM) transition when temperature decreases. The lanthanum substitution by Re induces a decrease of the T-C value as well as the destruction of the phase-separated state existing at low temperature in the parent compound La0.5Ca0.5MnO3. Field dependence of magnetization shows that all our samples are phase-separated ones even above T-C. The absolute values of magnetic entropy change vertical bar Delta S-M vertical bar for a magnetic applied field of 2 T for the doped samples are 0.78, 1.15 and 2.16 J kg(-1) K-1 for Re = Gd, Eu and Dy respectively at the Curie temperature T-C. The maximum values of vertical bar Delta SM vertical bar decrease with sigma(2) but La0.4Dy0.1Ca0.5MnO3 shows a different behavior that may be due to the huge magnetic moment of Dy3+ ion. All the substituted specimens show some anomalies in the temperature dependence of magnetic entropy change curves only for the high values of magnetic field which can be attributed to the metamagnetic transition. Arrott plots show that the substituted specimens exhibit a second-ordered transition from PM to FM state unlike the metamagnetic transition which is first order. (C) 2012 Elsevier B.V. All rights reserved.