Influence of the Host Lattice Electronic Structure on Dilute Magnetic Interactions in Polymorphic Cr(III)-Doped In2O3 Nanocrystals

The effect of the host lattice structure on the spectroscopic and magnetic properties of Cr3+-doped In2O3 nanocrystals is reported. The influence of the dopant ions on the nanocrystal growth allows for the solution-phase stabilization and separation of doped colloidal In2O3 nanocrystals having different crystal structures - stable cubic phase (bcc-In2O3) and metastable rhombohedral (rh-In2O3) phase - and comparative study of the electronic structure and magnetic properties of Cr3+ in both polymorphs. Investigations by a range of complementary spectroscopic techniques, including Raman, X-ray absorption and magnetic circular dichroism spectroscopies, revealed that the change in the In2O3 phase leads to distinctly different electronic structure of Cr3+ dopants, associated with a different nature of the substitutional doping sites and different electronic structure of the nanocrystal host lattice. Nanocrystalline films prepared from colloidal nanocrystals exhibit ferromagnetism at room temperature, although the average magnetic moment of Cr3+ in rh-In2O3 is an order of magnitude smaller than that in bcc-In2O3 samples. This difference in magnetization is associated with wider band gap of rh-In2O3 nanocrystals, which prevents effective hybridization of the defect donor band, as a mediator of the Cr3+ magnetic exchange interactions, and the Cr3+ 3d states at the Fermi level. The results of this work demonstrate that a change in the defect and electronic structures of the same semiconductor host lattice by nanocrystal phase control in solution allows for tuning of the magnetic properties of diluted magnetic semiconducting oxides.