Low-temperature neutron diffraction and magnetic studies on the magnetoelectric multiferroic Pb(Fe0.534Nb0.4W0.066)O3

We report detailed low-temperature magnetic and neutron diffraction studies on 0.8 Pb(Fe0.5Nb0.5)O-3-0.2 Pb(Fe0.67W0.33)O-3 which is written as Pb(Fe0.534Nb0.4W0.066)O-3 (PFWN) in the general form. Magnetic susceptibility measurement data show that PFN exhibits antiferromagnetic to paramagnetic transition (T-N) around 155 K (Matteppanavar et al. in J Mater Sci 50: 4980-4993. doi: 10.1007/s10853-015-9046-5, 2015). In the present solid solution, the magnetic susceptibility (x) shows Neel temperature enhanced up to around 187 K. Temperature-dependent neutron diffraction studies well support the tuning up of T-N from 155 to 187 K. On decreasing the temperature, for T\T-N (T-N = 187 K), an extra peak grows at scattering vector Q = 1.35 angstrom(-1), which indicates the onset of antiferromagnetic ordering. The observed magnetic structure is G-type antiferromagnetic with the propagation vector, k = [0.25, 0.5, 0.5]. The refined monoclinic lattice parameters (a, b and c), angle (beta), unit cell volume, derivative of unit cell volume, magnetic moments and integrated intensity of magnetic peak (111) show anomaly around the T-N, which is a manifestation of spin-lattice coupling. Also, the lattice parameters (a, b and c) and unit cell volume exhibit negative thermal expansion below T-N and a large thermal expansion above T-N.