Study of magnetic ordering in MnAlxCrxFe2−2xO4

The spinel solid solution series MnAlxCrxFe2−2xO4 with x=0.0–0.9 in steps of 0.1 was studied using powder X-ray diffraction profile refinement, magnetization measurement at 80 K using an applied magnetic field 3.18×105 A-turn/m, Mössbauer spectroscopy at 300 K and low field AC susceptibility measurements. We have seen that the increase of Cr3+ ions and Al3+ ions in B sites at the cost of Fe3+ ions leads the present system towards the Néel type of collinear ordering of spins. The negative quadruple shifting seen in Mössbauer results and high value of oxygen positional ‘u’ parameter indicate oblate type of deformation of 3d5 shell. The results indirectly support the theory of “exchange disorder” of Fe3+ ions in B sites as the cause of the reduction in magnetic moment for MnFe2O4 from Néel type of ordering. There is the emergence of ‘spin clusters’ in the long-range network of spins as indicated in the ac susceptibility and Mössbauer results at room temperature in x>0.7 compounds.