Ultraefficient microrefrigerators realized with ferromagnet-superconductor junctions

We prove that efficient electron cooling can be realized using ferromagnet-superconductor junctions. Cooling power densities up to 600 nW/mu m(2) can be achieved in this system, leading to electronic temperature reductions largely exceeding those obtained with existing superconductor-insulator-normal metal tunnel contacts. Furthermore, cooling efficiencies largely exceeding 20% can be reached in such microrefrigerators. Half-metallic CrO2/Al bilayers are suggested as ideal candidates for the implementation of the device.