Evidence for cluster glass ground state in the potential giant dielectric constant material Ba(Fe1/2Sn1/2)O3-δ

Abstract

We report the magnetic ground state of the technologically important giant dielectric constant material Ba(Fe1/2Sn1/2)O3-δ (BFSO) using detailed dc and ac magnetization and specific heat measurements. Our careful x-ray diffraction analysis confirms that BFSO is single phase and crystallizes in the cubic structure with the Pmm space group. Temperature-dependent dc susceptibility measurements reveal that magnetic irreversibility sets in below Tirr ~ 18 K. In addition, the zero-field cooled susceptibility exhibits a peak at the freezing temperature of Tf ~ 16 K, which is also characterized by a frequency dispersion in ac susceptibility measurements. This data also confirms to the critical slowing down model with cluster-glass transition temperature TG ~15.7 K and characteristic relaxation time τo ~10-7 s. The magnetic field dependence of the freezing temperature Tf obeys de Almeida-Thouless line in the H-T plane. The presence of aging effect and extremely slow time decay of thermoremanent magnetization is also observed below Tf. The magnetic contribution to the specific heat (Cm) exhibits a linear temperature dependence below Tf. All these observations unambiguously confirm a cluster-glass magnetic ground state in this system.