Modulating the optical and magnetic properties of geometrically frustrated ZnV2O4 by the introduction of indium (nonmagnetic ions), iron, and chromium (magnetic ions)

Abstract

The current study is aimed at understanding the effects of diluting the magnetic properties of a geometrically frustrated normal spinel, ZnV₂O₄, with the incorporation of nonmagnetic In³⁺ in place of V³⁺. Samples with the formula, ZnV_2−xIn_xO₄ (x = 0.00, 0.25, 0.50, 1.00 and 1.50), were synthesized following an epoxide mediated gel method and characterized extensively. The monophasic cubic spinel structure was retained up to 50 mol% of vanadium with indium, beyond which phase separation took place. The occupancy of indium at the octahedral site and the near-linear increment of the cubic unit cell constant were confirmed from the successful structural refinements. The optical bandgap increased from 2.80 (ZnV₂O₄) to 3.06, 3.19, and 3.35 eV for x values of 0.25, 0.50, and 1.00 in ZnV_2−xIn_xO₄. ZnVInO₄ exhibited paramagnetic behavior down to 2 K in both the field-dependent and temperature-dependent magnetic measurements. However, the magnetization values were lower than those of ZnV₂O₄. A frustration index of 42 was estimated for ZnVInO₄. Samples containing magnetic Cr³⁺ and Fe³⁺ ions in place of V³⁺ were synthesized and characterized to compare and contrast the magnetic ions’ influence. For both chromium and iron substituted samples, the optical bandgap was higher than that of ZnV₂O₄. ZnVCrO₄ showed an antiferromagnetic ordering of spins with a T_N of 12.3 K. In contrast, the randomization of Zn, V, and Fe among the available crystallographic sites increased the ferrimagnetic transition temperature (T_F) to 31.9 K. ZnVInO₄ catalyzed the photodegradation of rhodamine-6G under UV-vis radiation to a greater extent than ZnVCrO₄ and ZnVFeO₄.