Physical properties of MgAl2O4, CoAl2O4, NiAl2O4, CuAl2O4, and ZnAl2O4 spinels synthesized by a solution combustion method

Abstract MgAl 2 O 4 , CoAl 2 O 4 , NiAl 2 O 4 , CuAl 2 O 4 , and ZnAl 2 O 4 spinels have been synthesized by a solution combustion method following with secondary calcination. These aluminates were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, ultraviolet–visible spectroscopy, and scanning electron microscope. As-prepared samples show pure spinel phase with good crystalline, vivid colour, fine particle size, and porous structure. Phenomenon of anti-site disorder in these samples has been investigated, which shows dependence on the radius of the A-site ions. Magnetic properties and heat capacities of these samples were further characterized by magnetic property measurement system and physical property measurement system. Among the magnetic compounds, NiAl 2 O 4 is typical antiferromagnetic, CoAl 2 O 4 shows interesting spin-glass-like ground state, and CuAl 2 O 4 exhibits characteristic of spin liquid due to strong spin frustration and site inversion effects in the system. Heat capacities of these compounds are further studied. The values of the Debye and Einstein temperatures are given through fitting the data. Furthermore, the magnetic contribution Δ C m and magnetic entropies Δ S m of the magnetic samples are obtained after subtraction of the phonon contribution.