Magneto-dependent photovoltages and switching in permalloy metasurfaces*

Permalloy is a soft ferromagnetic material with very high magnetic permeability, commonly used in various magnetic and magnonic studies. Recently, it was found that permalloy structures demonstrate plasmonic behavior and an interesting coupling between optical, magnetic and electric effects, which makes them candidates for spintronic and nanomagnetic applications, and plasmon-induced magnetization switching.  Using E-beam evaporation, we deposited permalloy films on flat and profile modulated substrates with submicron periodicity. The photovoltages induced by laser pulse illumination show significant dependence on magnetic field with a characteristic hysteresis.  The switching fields depend on the geometry of the structure, being the lowest for flat films, and the highest for grating structures with high amplitude of profile modulation.  The photovoltage magnitude increases linearly with an increase in the illumination intensity when the external magnetic field is not in the range of the switching field.  More complicated dependence is observed at the range of the switching indicating possible photoinduced magnetization switching due to spin angular momentum transfer from light to matter.