Coercivity and Nano-structure in Magnetic Spinel Mg(Mn,Fe)$_{2}$O$_{4}$

We discovered that the micro-to-nano-structure of Mg(Mn,Fe)$_{2}$O$_{4}$ drastically changes with different thermal treatment. This extraordinary structural evolution is associated with spinodal chemical decomposition associate with the Jahn-Teller structural distortions around Mn ions. The magnetic properties of the polycrystalline Mg(Mn,Fe)$_{2}$O$_{4}$ vary with the structural progress. Particularly, the Curie temperature and magnetic coervcivity considerably change with the structural evolution. The significantly-enhanced coercivity in the system with elongated nanostuructre stems from the large shape anisotropy of the nanostructure.