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X-ray diffraction pressure studies at room temperature demonstrate that thespinel FeAl$_{2}$O$_{4}$ transforms to a tetragonal phase at ~18 GPa. Thistetragonal phase has a highly irregular unit-cell volume versus pressuredependence up to ~45 GPa, after which a transformation to a Cmcm post-spinelphase is onset. This is attributable to pressure driven Fe-Al site inversion atroom temperature, corroborated by signatures in the 57Fe M\"ossbauerspectroscopy pressure data. At the tetragonal to post-spinel transition, onsetin the range 45-50 GPa, there is a concurrent emergence of a non-magneticspectral component in the M\"ossbauer data at variable cryogenic temperatures.This is interpreted as spin crossover at sixfold coordinated Fe locationsemanated from site inversion. Spin crossover commences at the end of thepressure range of the tetragonal phase and progresses in the post-spinelstructure. There is also a much steeper volume change dV/V ~ 10% in the range45-50 GPa compared to the preceding pressure regime, from the combined effectsof the structural transition and spin crossover electronic change. At thehighest pressure attained, ~106 GPa, the M\"ossbauer data evidences adiamagnetic Fe low-spin abundance of ~50%. The rest of the high-spin Fe ineightfold coordinated sites continue to experience a relatively small internalmagnetic field of ~33 T. This is indicative of a magnetic ground stateassociated with strong covalency, as well as substantive disorder from siteinversion and the mixed spin-state configuration. Intriguingly magnetismsurvives in such a spin-diluted post-spinel lattice at high densities. TheR(300 K) data decreases by only two orders of magnitude from ambient pressureto the vicinity of ~100 GPa. Despite a ~26% unit-cell volume densification fromthe lattice compressibility, structural transitions and spin crossover.

Interplay between structural and magnetic-electronic responses of FeAl$_{2}$O$_{4}$ to a megabar: site inversion and spin crossover