Magnetism, magnetocaloric effect and magnetoresistance in electron-doped manganites R0.15Ca0.85MnO3 (R = Y, Nd, Gd and Dy)
ABSTRACT :
Correlated spin, lattice and charge degrees of freedom in perovskite oxides R1-xAxMnO3 (0 ≤ x ≤ 1) (R = rare earth such as La and Y, A= alkaline earth such as Ca and Sr) lead to intricate structure-property relationships. A simultaneous change of crystal structure and magnetic structure occurs around 125 -150 K in electron-doped manganites R0.15Ca0.85MnO3 where R = La, Y and Sm. Below the critical temperature, these oxides exhibit structural and magnetic phase coexistence. Thus motivated, we study magnetic, magnetocaloric and electrical transport properties of electron-doped R0.15Ca0.85MnO3 (R = Y, Nd, Gd and Dy) manganites. These oxides have orthorhombic crystal structure (space group Pnma, No. 62) at 300 K and undergo paramagnetic to antiferromagnetic transition at 113 K, 112 K, 115 K and 117 K (TN), respectively. While thermal hysteresis in magnetization and electrical resistivity around TN suggests a first order transition, the observation of metamagnetism below TN indicates the presence of competing magnetic interactions. Powder neutron diffraction study on Nd0.15Ca0.85MnO3 indeed confirms the change of crystal structure to a monoclinic (space group P21m, No.11) type around its Néel temperature. Colossal magnetoresistance and the sign-changing magnetocaloric effect observed below TN are likely the result of coexisting, competing phases.