The consequences of the pressure-induced \textit{spinel }-- \textit{post spinel} transition upon the electronic properties of MgFe$_{2}$O$_{4}$

Similar to magnetite the ferrimagnetic magnesioferrite (SG \textit{Fd3m} T$_{N} =$ 710 K) is a an \textit{inverse} spinel (Fe$^{3+}$)$_{A}$(Mg$^{2+}$Fe$^{3+}$)$_{B}$ in which the $A$ and $B$ are 4- and 6- coordinated moieties, respectively. At $\sim$ 25 GPa a 1$^{st}$ order structural transition takes place into a denser, the so called, post-spinel (\textit{ps}) structure. The few studies carried out so far concluded that the \textit{ps} structure is either of the CaMn$_{2}$O$_{4}$ or CaTi$_{2}$O$_{4}$ -type. Our preliminary HP M\"{o}ssbauer studies (MS) have unambiguously revealed two Fe sites contradicting the one Fe-site typical of the CaMn$_{2}$O$_{4}$ or the CaTi$_{2}$O$_{4}$ polymorphs. This presentation describes the evolution of the electronic/magnetic properties of the \textit{ps} phase of MgFe$_{2}$O$_{4}$ up to 80 GPa. Experiments at variable-T were carried out with MS and electrical resistance $R$ both at compression and decompression. At 47 GPa (\textgreater $P_{s\to ps})$ the M\"{o}ssbauer spectra reveals a paramagnetic state at RT composed of two -quadrupole-split sites which magnetically orders at \textit{T \textless T}$_{N}$ ($=$ 220 K). Two fully magnetic split components are present at T \textless 53 K. $R(P$, 300K) $ R(P)$ increases sharply reaching a peak at 20 GPa and drops continuously by 10$^{-6}$ at $P$ \textgreater 50 GPa. By decompression to $\sim$ 4 GPa the electronic/magnetic properties remain typical of the \textit{ps} phase.