Spin reorientation and giant dielectric response in multiferroic La1.5Sr0.5NiO4+δ

A multiferroic sample of La1.5Sr0.5NiO4+δ was prepared by conventional solid-state reaction. X-ray diffraction study revealed La1.5Sr0.5NiO4+δ 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 (δ) in the La1.5Sr0.5NiO4+δ ceramic. We found δ = −0.017, which corresponds to a doping level of nh = x + 2δ = 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 e (ω , T) = e′(ω,T) − ie ″(ω,T) was estimated by basing on capacitance and conductance curves measured at different temperatures and frequencies. Dielectric relaxations of charge-ordered La1.5Sr0.5NiO4+δ 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.