Spin reorientation and giant dielectric response in multiferroic Lai 1.5Sr0.5NiO4+γ

Abstract

A multiferroic sample of Lai1.5Sr0.5NiO 4+γ was prepared by conventional solid-state reaction. X-ray diffraction study revealed LaL5Sra5NiO4+a exhibiting a single phase with a tetragonal structure (F4K2Ni-perovskite-type structure, and space group of I4/mmm). An iodometric titration method was used to determine non-stoichiometric oxygen concentrations (5) in the LaL5Sra5NiO4+a ceramic. We found 5 = -0.017, which corresponds to a doping level of nh = x + 25 = 0.466 (with x being Sr2+ content). The field-cooled (FC) magnetization curve indicated that there was a strong increase in spin ordering (SO) at temperature TSO∼ 100 K. Below TSR∼ 50 K, spins undergo a spin reorientation (SR) turning away from the stripe direction on cooling. Its dielectric constant s(co, T) = e'(co, T) - ie"(co, T) was estimated by basing on capacitance and conductance curves measured at different temperatures and frequencies. Dielectric relaxations of charge-ordered LaL5Sra5NiO4+a ceramic were investigated in a broad temperature range. The giant dielectric constant (104-106) with a low dielectric loss of 10-2-10-1 was also found. © 2013 Vietnam Academy of Science & Technology.