Nonequilibrium Cation Distribution, Canted Spin Arrangement, and Enhanced Magnetization in Nanosized MgFe₂O₄ Prepared by a One-Step Mechanochemical Route

Abstract

A single-step synthesis of magnesium ferrite (MgFe2O4) nanoparticles with an average crystallite size of about 8.5 nm synthesized via mechanochemical processing of binary oxide precursors at room temperature is reported. The study highlights the nature of the cation disorder and of the spin arrangement in mechanosynthesized MgFe2O4 as well as its response to changes in temperature. An unusual property of the magnetization enhancement in nanoscale mechanosynthesized MgFe2O4 is reported. Whereas the inner core of a MgFe2O4 nanoparticle exhibits a partly inverse spinel structure with a Néel type collinear spin alignment, the major features of the ionic and spin configurations in the grain boundary (surface) region are a nonequilibrium cation distribution and a canted spin arrangement. Although the spin-canting effect tends to reduce the magnetic moment, the magnetization enhancement exhibited by mechanosynthesized MgFe2O4 is attributed to the nearly random distribution of magnetic cations in the surface regions of nanoparticles. On heating above 623 K, the mechanosynthesized MgFe2O4 relaxes to a structural and magnetic state that is similar to the bulk one.