Structural and magnetic studies on perovskite rare-earth manganites (Nd1−xGdx)0.55Sr0.45MnO3 (x=0, 0.1, 0.3 and 0.5): Observation of two-step magnetization and negative magnetization behavior

Abstract The effect of smaller and heavy rare-earth cation Gd 3+ ( r Gd 3+ =1.107 A and S G d 3 + = 7 / 2 ) on the magnetic and structural properties of Nd 0.55 Sr 0.45 MnO 3 has been investigated. The orthorhombic structure (space group, Pnma ) evolves from orbital distorted- O ” type symmetry ( c > a ) for x =0 to orbital ordered- O ’ type ( a > c ) for x ≥ 0.1 . Diffraction data shows the crucial role of the shear strains involved in the structure. The magnetization measurement shows two magnetic transitions occurring in compounds x ≥0.1. Spectacular feature was observed in the heavily Gd-doped sample ( x =0.5) such as: the continuous increase of M with high magnetic field, the low value of saturation magnetization at low temperature, the metamagnetic transition, and the presence of exchange bias. These findings are interpreted as the fingerprints of the phase separation. Our result indicates that the martensitic accommodation strain, in addition to quenched disorders, may be an alternative approach to understand the physical phase separation. The interesting feature for x =0.5 sample is the negative magnetization observed at low field. Result is interpreted in terms of two interacting networks, with negative exchange interaction between the (Gd+Nd) and the ferromagnetic Mn lattices. The disappearance of the negative magnetization for magnetic field well below the coercive field (~0.047 T) suggest that the magnetic properties of x =0.5 behaves as an inhomogeneous ferrimagnet at low field.