Efforts towards spin-polarized scanning tunneling microscopy of MnAs thin films on gallium arsenide
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The available Omicron variable-temperature scanning tunneling microscope (VT-STM) was modified in order to enhance its capabilities and include the possibility of spin-polarized measurements. A lock-in amplifier was installed, enabling the researcher to obtain scans of the differential conductance dI/dU, which allow deduction of the magnetic domain structure. The applicability of ferromagnetic tips made of Co, and of Pt-tips covered by e-beam evaporation with antiferromagnetic Cr thin films was investigated. Those tips were used to study two different MnAs thin films (40 and 400 nm) previously grown epitaxially on GaAs(001) substrates. The goal was to image the magnetic structure of the ferromagnetic MnAs phase reported from MFM measurements, and to enhance the resolution to the atomic level provided by the STM. It turns out that for several reasons, which are explained in the final section, spin-polarized measurements on existing MnAs films were not successful when using the available devices.