  The field of lead halide perovskite nanocrystal doping has witnessed notable
progress in recent times, leading to the creation of innovative materials that
showcase compelling physical characteristics and hold substantial technological
promise. The true characteristics of these materials lie in the presence of
dopant-carrier magnetic exchange interactions. This work presents the first
direct observation of such exchange interactions in colloidal Mn-doped
CsPbX$_3$ (X= Cl, Br) quantum dots (QDs). Here, we employ magnetic circular
dichroism (MCD) spectroscopy to unambiguously demonstrate the successful doping
and the presence of giant excitonic Zeeman splitting in CsPbX$_3$ (X= Cl, Br)
QDs doped with Mn$^2$$^+$. The controllable tuning of effective exciton
g-factors (g$_e$$_f$$_f$) within the range of 2.1 to (-)314 has been achieved
through the process of doping with 6.9 % Mn in CsPbCl$_3$, which will
facilitate their application towards future spintronics
