Cation distribution and entropic disordering in mixed spinel ferrite Ga_0.4Fe_0.6NiCr_1−yAl_yO₄

Abstract

Mössbauer measurements (4.2≤T≤298°K) indicate the presence of entropic disordering in (Ga_0.4³⁺Fe_0.6³⁺Al_p³⁺) [Ni²⁺Cr_1−y³⁺Al_y−p³⁺Fe_p³⁺]O₄ and a linear increase in p with y between 0(y=0) and 0.11(y=1). Entropic spins are located only on A-sites indicating relatively large A-sublattice frustration. Weak A-B coupling could explain this separate sublattice behaviour. Magneton number, alongwith Mössbauer p values, shows B-site canting which increases with y revealing weakness of A-B interaction. Present system can be called a "frustrated ferrimagnet" or "entropie ferrimagnet" where ferrimagnetic and frustrated (entropie) spins are coexisting.