Structural and magnetic properties of amorphous ferric molybdate compared to crystalline ferric molybdate

The two component system Fe₂ (MoO₄)₃. MoO₃ denoted as CFM (crystalline ferric molybdate) has been transformed to the amorphous state by application of shearing stress under high pressure. The transition from amorphous ferric molybdate (AFM) to CFM can be achieved by air annealing of AFM at T>550 K. A detailed study of the crystallization process has been performed by Mössbauer, X-ray and microcalorimetric measurements. A proposal for the “structure” of the amorphous state and for the crystallization process is made. Below the Néel temperature (T_N=13 K) CFM orders weakly ferrimagnetic, whereas the magnetic ordering of AFM occurs below 4.2 K with a still unknown magnetic phase.