Effect of Cu and Zn substitution on the structure and magnetism of NdMnO₃ manganites

RMnO₃ type manganite materials, where R is a rare-earth metal, are known to exhibit variety of interesting physical properties such as insulator to metal transition, ordering from a paramagnetic to ferromagnetic state, colossal magnetoresistance etc., which make them potential candidates for spintronic applications. NdMnO₃ exhibits antiferromagnetic ordering (T_N ~ 78 K) along with coexistence of antiferromagnetic and ferromagnetic interactions and reorientation of Mn spins at low temperatures. Substitution is an ideal tool for modifying the physical properties, particularly in manganite. In the present work, we have substituted Cu and Zn at Mn site to understand the influence a magnetic or a non-magnetic ion at Mn site will have on the structure and magnetism of NdMnO₃. The magnetic properties have been studied by magnetization measurements as a function of temperature and magnetic field. Crystallographic structural properties have been obtained from room temperature neutron diffraction studies. Temperature dependent neutron diffraction studies were carried out to understand the magnetism of this compound via the modifications observed in the magnetic structure as a function of temperature. Analysis of room temperature ND data confirms single phase formation of NdMn_1-xM_xO₃ (x = 0.05; M = Cu and Zn) compounds, crystallizing in orthorhombic perovskite structure with Pnma space group. Field and temperature dependent magnetization measurements show magnetic anisotropy and negative magnetization in pure and doped NdMnO₃. Temperature dependent neutron diffraction patterns show that the magnetic peak appears below T_N ~ 75K and becomes stronger in intensity with decreasing temperature. Detailed analysis of temperature dependent neutron diffraction and magnetization data will be presented and discussed in the light of the observation of negative magnetization and evolution of magnetic structure of NdMn_1-xM_xO₃ (x = 0.05; M = Cu and Zn) compounds below and above their respective magnetic ordering temperatures.