Enhanced Magnetic Properties of In–Mn-Codoped Plasmonic ZnO Nanoflowers: Evidence of Delocalized Charge Carrier-Mediated Ferromagnetic Coupling

Abstract

We report a detailed study of temperature and magnetic field dependence of the magnetization of free-standing colloidal Mn-doped and In–Mn-codoped ZnO nanoflower (NF) powders, including their optical spectroscopic properties to explore the delocalized charge carrier (conduction band electron)-mediated ferromagnetic coupling in dilute magnetically doped semiconductor (DMS), which could empower the next-generation spin-based information technologies. In the present investigation, all samples are characterized by the hexagonal wurtzite (P63mc) crystal structure, although the hexagonal shape of pure ZnO nanocrystals is transformed into the flowerlike morphology with Mn doping and In–Mn codoping. The Zn interstitial defects, traced through the blue photoluminescence emissions, have been found to form bound magnetic polarons (BMPs) in the presence of spin-↑ Mn2+ ions in Zn0.9Mn0.1O NFs. The overlapping of these BMPs typically leads to above-room-temperature ferromagnetism in Zn0.9Mn0.1O NFs. Exclusively, the significant enhancement in magnetization value at 50 kOe (∼18%) and coercivity (∼10 times) have been identified on codoping with In3+ ions, i.e., for Zn0.8In0.1Mn0.1O NFs, originating from the delocalized conduction band electrons as evident from the plasmonic absorption, which induce new ferromagnetic coupling between Mn2+ ions via themselves. Here, we unfold for the first time a truly fascinating phenomenon of delocalized charge carrier-mediated ferromagnetic coupling in In–Mn-codoped plasmonic ZnO NFs, which significantly improves the ferromagnetism in Mn-doped ZnO DMSs.