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

Dang Thanh Tran, Dinh LamVu, Van Hong Le, The-Long Phan and Seong-Cho Yu

Abstract

A multiferroic sample of La_1.5Sr_0.5NiO_4+δ was prepared by conventional solid-state reaction. X-ray diffraction study revealed La_1.5Sr_0.5NiO_4+δexhibiting 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 La_1.5Sr_0.5NiO_4+δ ceramic. We found δ = −0.017, which corresponds to a doping level of n_h = 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 T_SO ~ 100 K. Below T_SR ~ 50 K, spins undergo a spin reorientation (SR) turning away from the stripe direction on cooling. Its dielectric constant ε (ω , T) = ε'(ω,T) − iε ''(ω,T) was estimated by basing on capacitance and conductance curves measured at different temperatures and frequencies. Dielectric relaxations of charge-ordered La_1.5Sr_0.5NiO_4+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