Effect of Molybdenum Doping o the Magnetism Properties of Cobalt Ferrite*

This work investigates the effect of molybdenum (Mo) doping on the magnetic properties of cobalt ferrite (CoFe$_{2}$O$_{4}$, referred to CFO) polycrystalline material. Mo incorporated CFO (CoFe$_{2-}_{x}$Mo$_{x}$O$_{4,\, }$referred to CFMO) ceramics were prepared by solid-state reaction by varying the Mo concentration ($x=$0.0-0.3). X-ray diffraction studies indicate that the CFMO materials crystallize in inverse spinel cubic phase. Mo doping increases the lattice parameter from 8.322 to 8.343 {\AA}. We noticed ferromagnetic-like behavior from all the samples studied, in which, the Curie temperature is found to be close to 300 K. Furthermore, we find almost 2-fold decrease in coercive field (H$_{c})$ from 2143 Oe to 1145 Oe with the increase in Mo doping up to 30{\%}, and is consistently observed at all the temperatures measured (4, 100, 200 and 300 K). In addition, the saturation magnetization estimated at 4 K and at 1.5 T goes through a peak at 92 emu/g (at 15{\%} Mo doping) from 81 emu/g (pristine CFO), and starts decreasing to 79 emu/g (at 30{\%} Mo doping). Our experimental findings led us to believe that the magnetic properties observed here could be due to the complex interplay of double-exchange and super exchange interactions between Fe$^{3+}$/Fe$^{2+}$ via Mo$^{6+}$.