  Magnetic fluctuations in transition metal oxides are a subject of intensive
research because of the key role they are expected to play in the transition
from the Mott insulator to the unconventional metallic phase of these
materials, and also as drivers of superconductivity. Despite much effort, a
clear link between magnetic fluctuations and the insulator-to-metal transition
has not yet been established. Here we report the discovery of a compelling link
between magnetic fluctuations and the insulator-to-metal transition in
Ca(Ir$_{1-x}$Ru$_{x}$)O$_{3}$ perovskites as a function of the doping
coefficient x. We show that when the material turns from insulator to metal, at
a critical value of x$\sim$ 0.3, magnetic fluctuations change their character
from antiferromagnetic, a Mott insulator phase, to ferromagnetic, an itinerant
electron state with Hund's orbital coupling. These results are expected to have
wide-ranging implications for our understanding of the unconventional
properties of strongly correlated electrons systems
