Normal and inverse magnetocaloric effect in colossal magnetoresistive electron-doped manganites R0.15Ca0.85MnO3 (R = Y, Gd and Dy)

Abstract Magnetic, magnetocaloric and electrical transport properties of polycrystalline R 0.15 Ca 0.85 MnO 3 (R = Y, Gd and Dy) manganites (Orthorhombic, Pnma ) have been studied. Magnetization measured in 5 kOe field reveals antiferromagnetic transition at 111 K, 119 K and 112 K (T N ) respectively in R 0.15 Ca 0.85 MnO 3 (R = Y, Gd and Dy). Magnetization in the ordered state undergoes field-induced transition and at 2 K, in 140 kOe field, the magnetic moment values are 1.5 μ B /f.u., 2.8 μ B /f.u. and 2.7 μ B /f.u. respectively for R 0.15 Ca 0.85 MnO 3 (R = Y, Gd and Dy) samples. While the electrical resistivity above T N shows non-adiabatic, small polaron hopping behavior, the resistivity value increases rapidly below T N . Hysteresis is observed around T N between field cooled cooling (FCC) and field cooled warming (FCW) magnetization data in 100 Oe and also between the cooling and warming data of zero-field electrical resistivity. Electrical resistivity exhibits a metal to insulator-like transition at T N in applied magnetic fields of 50 kOe and above. Colossal, negative magnetoresistance of ∼82%, 85% and 76% is observed at 50 K in 50 kOe field in R 0.15 Ca 0.85 MnO 3 (R = Y, Gd and Dy) manganites. Magnetocaloric effect (MCE) is estimated in terms of isothermal magnetic entropy change (ΔS m ) and inverse MCE (+ΔS m ) is observed in the antiferromagnetically ordered state. The ΔS m changes sign for field changes greater than the metamagnetic critical magnetic field (H c ). Sign changing MCE signifies the evolution of underlying mixed magnetic interactions in these systems with variations in magnetic field and temperature.