Large voltage from spin pumping in magnetic tunnel junctions

We studied the response of a ferromagnet–insulator–normal metal tunnel structure under an external oscillating radio frequency (rf) magnetic field. The dc voltage across the junction is calculated and is found not to decrease despite the high resistance of the junction; instead, it is of the order of 1–100 μV, much larger than the experimentally observed value (100 nV) in the “strongly coupled” Ohmic ferromagnet–normal metal bilayers. This is consistent with recent experimental results in tunnel structures, where the voltage is larger than microvolts. The damping and loss of an external rf field in this structure are calculated.