Large asymmetry in the magnetoresistance loops of ferromagnetic nanostrips induced by Surface Acoustic Waves

In this work we show that Surface Acoustic Waves (SAW) can induce a very large asymmetry in the magnetoresistance loop of an adjacent ferromagnetic nanostrip, making it look as if it had exchange bias. The Surface Acoustic Wave induces a DC voltage in the ferromagnetic nanostrip. For measurements at constant current, this DC voltage makes the AMR loop asymmetric. In a series of different electrical experiments, we disentangle two different contributions to the induced DC voltage. One of them is independent on the external magnetic field and it is likely due to the acoustoelectric effect. A second contribution depends on the external magnetic field and it is a rectified voltage induced in the piezoelectric substrate as a response to the magnetization dynamics in the magnetostrictive nanostrip. The large asymmetry in the magnetoresistance loop reported in this work is a manifestation of an effective transfer of energy from the SAW to the magnetization dynamics, a mechanism that has been very recently appointed as a possible mean to harvest energy from a heat source.