The current work establishes the excitonic magneto-optic (M − O) effects of magnetic circular dichroism (MCD) in Cobalt (Co2+) doped diamagnetic organic−inorganic hybrid CH3NH3PbBr3 perovskites at low magnetic field and room temperature. The solution-processed perovskites are prepared in the form of single crystal thin films and quantum dots. The structural studies confirm the successful doping of the Co2+ in the perovskite lattice. Further, the perovskites are investigated as diluted magnetic semiconductors (DMSs) related to the dopant concentration effect and the size effect on their M − O properties. Magnetic dopant Cobalt leads to the strong sp-d exchange coupling that generates higher values of Zeeman splitting (ΔEZ) than the pristine MAPbBr3 due to the excitonic 1s Pb–Br absorption quantified by analysis of MCD. The ΔEZ value increases with the Co concentration up to 10 mol % and then starts decreasing. This concentration dependency can be linked with the luminescence of the perovskites with the Co2+ doping. The rise and fall of the MO and PL properties can be defined by the formation of Co–Co pairs in heavily doped perovskites which can influence the spin conditions of the paramagnetic Co ions. Using the Kramers–Kronig relations with MCD, the calculated Verdet constant exhibits a massive increase in value with the doping of cobalt, much higher than the industry standard Faraday rotator indicating their probable usability in this industry. Further in the quantum dots, the quantum confinement effect is pronounced that increases the MCD and hence the ΔEZ multiple times higher than the bulk perovskite films. These results provide a promising pathway for the study of solution-processed hybrid perovskites as DMSs for spintronics.
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