Reexploring the cation ordering and magnetic cation substitution effects on the elastic anisotropy of aluminum spinels

We study the effects of cation inversion x (Mg ↔ Al, with x representing the fraction of Mg and Al exchanged) and magnetic substitution (Mn → Mg) on the elastic properties of the MgAl 2O 4 spinel system using density functional theory and Brillouin scattering techniques. Our computations show that cation inversion decreases the molar volume of spinel and produces a stiffening of C 11 and a softening of C 12. Simulations and experiments agree within 2 %. Density functional theory also captures the qualitative effect of Mg ↔ Al on C 44, that is, an initial softening for inversion degree at x < 0.125 and stiffening at x = 1, with a disagreement of