Abstract

Surface iodine hole doping in vanadium oxide nano and microstructures was achieved through a simple iodine sublimation treatment, enabling controlled surface electronic modification while largely preserving the bulk crystalline framework. The magnetic response of iodine treated vanadium oxide nanostructures, including multiphase cog like systems associated with V4O7/V5O9 domains, (C18H37NH3)2V7O16 nanourchins, and layered (NH4)2V7O16 microsquares, was systematically investigated. The untreated nanostructures already contain frustrated mixed valence environments capable of supporting localized magnetic moments; however, strong magnetic compensation suppresses cooperative magnetic retention. Iodine treatment acts primarily as a surface perturbation that modifies preexisting exchange pathways through hole doping and defect generation rather than creating magnetism in an intrinsically nonmagnetic system. Weak ferrimagnetic contributions emerged exclusively in nanostructures with high surface exposure and greater structural flexibility, namely nanocogs and nanourchins, whereas the microsquares retained a predominantly frustrated antiferromagnetic character following iodine treatment. In nanocogs, the coexistence of V4O7 and V5O9 related domains promotes incomplete magnetic compensation between competing exchange interactions. In nanourchins, the magnetic response is associated with defect rich V7O162- nanotubular walls, while the layered V2O5 like core continues to suppress long range cooperative alignment. Magnetic measurements revealed weak hysteresis at low temperatures for nanocogs and nanourchins, while persistent ZFC-FC irreversibility in microsquares indicated dominant magnetic frustration. Structural analyses confirmed that iodine induced modification remains primarily confined to the surface, without major alteration of the bulk crystal structure. These findings demonstrate that morphology, defect distribution, and surface electronic modification collectively influence the magnetic behavior of reduced vanadium oxide systems, providing insight into defect mediated magnetic tuning in structurally frustrated complex oxides.