Implications of including a magnetic ion (Cr3+ and Fe3+) at the vanadium site in geometrically frustrated spinel MgV2O4: Magnetic and Catalytic properties
The vanadium sublattice in geometrically frustrated MgV2O4 is substituted partially with Cr3+ and Fe3+. From successful Rietveld refinement of powder X-ray diffraction patterns of MgVCrO4 and MgVFeO4, Cr and Fe occupy octahedral sites of spinel structure. Extensive field-dependent and temperature magnetic measurements on these samples reveal exciting results. MgV2O4 remained paramagnetic till 3 K, with a small divergence at around 20 K between ZFC and FC data. MgVCrO4 exhibits antiferromagnetic behavior with a Neel temperature of 13.6 K. MgVFeO4 shows spin-glass behavior resulting from the frustration with a glass transition temperature of 194 K. This sample shows a typical ferromagnetic behavior, with a coercivity of 194.5 Oe within an applied field of ± 2kOe. All three systems have been found to have frustration index in the range 1-25, and effective magnetic moment decreased in the order MgVFeO4 > MgVCrO4 > MgV2O4. While the inclusion of chromium did not alter the bandgap of MgV2O4, iron substitution increased bandgap. The partial replacement of V3+ with Cr3+ and Fe3+ appended catalytic property to the system in terms of oxidative degradation of methylene blue dye. The catalytic efficiency followed the order MgVFeO4 > MgVCrO4 > MgV2O4 matching well with the trend noticed in the porosity, surface area, red-ox ability of Fe3+, Cr3+ and V3+ in these samples. The degradation pathway has been followed by analyzing the intermediates from these experiments by mass spectrometry and a plausible mechanism proposed.