Room temperature neutron diffraction and magnetic studies on PbFe_0.5Nb_0.5O₃-BiFeO₃ solid solutions

Magnetoelectric multiferroics are the materials with a coexistence of two ferroic orders such as ferroelectric and ferromagnetic orderings at a certain temperature in a single material. Among them, PbFe_0.5Nb_0.5O₃-BiFeO₃ (PFN) is a well-known A(B′_1/2B′′_1/2)O₃ type multiferroic exhibiting magnetoelectric coupling below its Neel temperature (T_N) - 155 K and it undergoes paraelectric to ferroelectric transition at T_C = 385 K. BiFeO₃ (BFO) is the only room temperature magnetoelectric multiferroic and its T_N is 643 K and T_C is 1103 K. It is well reported in the literature that synthesis of both PFN and BFO with single phase has been difficult by the conventional methods, due to the formation of unwanted pyrochlore phases such as Pb₂Nb₂O₇, Bi₂Fe₄O₉, etc. In order to tune T_C and T_N of PFN at and above room temperature, here we made an attempt to synthesize single phase (1-x) PFN - (x) BFO solid solutions with x = 0.1, 0.2, 0.3 and 0.4 by single step solid state reaction method. Structural studies have been carried out through XRD and it reveals the formation of single phase and also we observed the structural phase transition from monoclinic (Cm) to rhombohedral (R3c) at x = 0.4. In order to understand the nuclear and magnetic structure, room temperature neutron diffraction studies were carried out for all the solid solutions. Neutron Diffraction studies reveals the origin of magnetic ordering at x = 0.2 onwards and it confirms the G type antiferromagnetic ordering. Room temperature Electron Paramagnetic Resonance showed the paramagnetic nature for x = 0.1 and 0.2 whereas for x = 0.3 and 0.4 it shows the antiferromagnetic origin. Temperature dependent magnetic susceptibility shows the tuning of T_N from 230K to 350K for x = 0.1 to 0.4. Temperature dependent dielectric studies are the evidence of existence of magnetoelectric coupling. (author)