Electric field effects on magnetic and optical properties of MnAs/GaAs[001] thin films

Effects on magnetic and optical properties of perpendicular electric fields up to 1 MV/m were studied on thin ferromagnetic films of MnAs grown epitaxially on GaAs(001) substrates. Film thicknesses were 20, 50, 100 and 200 nm. With positive electric field corresponding to positive polarity of the MnAs film with respect to the GaAs substrate, it was found that at a field magnitude of 1 MVlm: (a) the magnetizations of the 20 and 50 nm films decreased by 3.5 and 1 percent, respectively, under both positive and negative fields as measured by vibrating sample magnetometry; (b) the magnetooptical Kerr effect (MOKE) of the 20 nm samples decreased by 3.5 percent in negative field but was unchanged by positive field; (c) the index of refraction of the 20 nm films determined by ellipsometry increased by 1 percent in positive field but was unchanged by negative field. No effects were found in thicker films, indicating the observed effects arise from the region of MnAs near the substrate. The MOKE signal of the 20 nm films has a power law dependence on electric field with an exponent of 0.36 with a standard deviation of 0.04. The intensity of the (10-10) x-ray diffraction peak from the ferromagnetic, hexagonal MnAs phase of a 20 nm film decreased by 5 percent in both positive and negative fields of 1 MV/m; however, there was no corresponding increase in the nonmagnetic, orthorhombic phase.