Dynamics of Surface Spins in Small Core–Shell Magnets of Li0.35Zn0.30Fe2.35O4 Bonds over a Carbon Surface and Tailored Magnetic Properties

The lithium zinc ferrite Li0.35Zn0.30Fe2.35O4 breeds Fe3+/Fe2+ spins via O2– of a network, which is what governs its magnetic and other properties for applications. When the oxygen polygons on the cations bond over an sp2-carbon layer, it keeps small crystallites of sample separated apart in single domains. Cuboids or rectangular prisms (Dc = 25 nm average size) of the ferrite are formed on an inorganic–organic gel, which is burnt in a self-propagating combustion in air. On annealing at ≥400 °C, residual carbon burns out yielding bare ferrite that grows successively; Dc ∼ 65 nm in 2 h at 800 °C. Distinct facets grown over plates (crystallites) turn up in a bonded carbon that desorbs off the surface at higher temperatures. At room temperature, a maximum Hc = 81 Oe (Ms = 85.6 emu/g) is shown in ferrite bonds over a thin carbon layer on Dc = 65 nm sample. With Hc = 4 Oe and Ms = 72.2 emu/g, in a virgin sample Dc = 25 nm. At ≥800 °C, a feroxol layer replaces carbon with 1150, 1325, and 1385 cm–1 phonon bands....