Core-coil devices operate by electromagnetic induction and include inductors, transformers, and electromagnets. Cooled core-coil devices include a magnetic core having a channel through it, and a coil wound around the core. Cooled core-coil devices additionally include a coolant loop that carries ferrofluid coolant through the channel and forms a loop with the channel that extends outside the core. Ferrofluid coolant circulates in the loop without a pump due to a thermo-magnetic response to the device's thermal and magnetic field gradients and thereby cools the core while simultaneously adding to the device's inductance.