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The magnetic properties and magnetocaloric effect of La_1.2Nd_0.2Ca_1.6Mn₂O₇ and La_1.2Sm_0.2Ca_1.6Mn₂O₇ are reported. The magnetic measurements indicate a second-order magnetic transition for La_1.2Nd_0.2Ca_1.6Mn₂O₇ and a first-order one for La_1.2Sm_0.2Ca_1.6Mn₂O₇. The decrease of the Curie temperature from ~247 K to ~198 K and ~176 K when La is substituted by Nd and Sm, respectively, can be correlated with the structural changes. The magnetic entropy changes determined from magnetization isotherms are higher for La_1.2Sm_0.2Ca_1.6Mn₂O₇ (6.45 J/kgK for ΔH = 4 T) than for La_1.2Nd_0.2Ca_1.6Mn₂O₇ (3.8 J/kgK for ΔH = 4 T). The high calculated values of the relative cooling powers in low magnetic field suggest the possibility to use these materials for magnetic refrigeration devices.

Keywords: double layered manganites, magnetization, magnetocaloric effect