Physical properties of MgAl 2 O 4 , CoAl 2 O 4 , NiAl 2 O 4 , CuAl 2 O 4 , and ZnAl 2 O 4 spinels synthesized by a solution combustion method

MgAl2O4, CoAl2O4, NiAl2O4, CuAl2O4, and ZnAl2O4 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, NiAl2O4 is typical antiferromagnetic, CoAl2O4 shows interesting spin-glass-like ground state, and CuAl2O4 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 ΔCm and magnetic entropies ΔSm of the magnetic samples are obtained after subtraction of the phonon contribution.