Study of magnetic ordering in MnAl xCr xFe 2−2xO 4

Abstract

The spinel solid solution series MnAl x Cr x Fe 2−2 x O 4 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 3.18×10 5 A-turn/m, Mössbauer spectroscopy at 300 K and low field AC susceptibility measurements. We have seen that the increase of Cr 3+ ions and Al 3+ ions in B sites at the cost of Fe 3+ 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 3d 5 shell. The results indirectly support the theory of “exchange disorder” of Fe 3+ ions in B sites as the cause of the reduction in magnetic moment for MnFe 2O 4 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.