Dl Abraham

Interface magnetism studied by optical second harmonic generation

Optical second harmonic generation studies of Co/Au interfaces show a clear magnetic field induced effect at these interfaces, leading the way to a nonlinear optical probe that is uniquely sensitive to surface and interface magnetism.

Near‐field magneto‐optical imaging in scanning tunneling microscopy

Images of magnetic bits written in a Pt/Co multilayer are presented. Using photosensitive semiconducting tips in a scanning tunneling microscope, both surface topography as well as polarization‐dependent optical transmission are measured. Magnetic contrast is achieved by detection of the Faraday effect. Magneto‐optical lateral resolution of 250 nm is demonstrated.

Photoamperic probes in scanning tunneling microscopy

The charge generated at the apex of a semiconductor tip upon laser irradiation is utilized in a scanning tunneling microscope. We show such arrangements can produce photoinduced tunnel currents of several hundred picoamperes, sufficient for stable STM operation and sensitive enough to detect nanowatt variations in the incident optical power.

Spin-dependent transmission at ferromagnet/semiconductor interfaces

We have measured the polarization-dependent photoresponse of ferromagnet-insulator-(III–V) semiconductor thin film tunnel structures as a function of wavelength. When the structures have no interfacial barrier, we find that the response agrees well with calculations of magneto-optical transmission through the magnetic overlayer. However, when a tunnel barrier is present and the excitation is nearly resonant with the semiconductor bandgap, we observe significant deviations from the magneto-optical effects. These deviations are attributed to spin-dependent electron transmission from the III–V semiconductor acting as a spin-polarized source of tunneling electrons.

Progress toward spin‐sensitive scanning tunneling microscopy using optical orientation in GaAs

Advances toward spin‐sensitive scanning tunneling microscopy are reported here, using optically created spin polarized electrons in GaAs. As a first step, tunneling spectroscopy has been performed on GaAs samples with light excitation. Dependence of photoinduced effects on excitation power, tip–sample distance, and doping density are presented. Similar measurements were conducted for a cleaved GaAs tip, showing short circuit currents of several hundred pA upon laser illumination. Results support the feasibility of using such tips as a spin‐sensitive local probe.

Scanning tunneling microscope for magneto-optical imaging

Images of magnetic bits written in a Pt/Co multilayer are presented. Using photosensitive semiconducting tips in a scanning tunneling microscope the surface topography as well as the polarization‐dependent optical transmission are measured. Magnetic contrast is achieved by detection of the Faraday effect. Magneto‐optical lateral resolution of 250 nm is demonstrated.

Surface structure of Fe/sub 3/O/sub 4/(110) studied by scanning tunneling microscopy

We have studied the [110] surface of magnetite Fe/sub 3/O/sub 4/ with a UHV scanning tunneling microscope (STM). The surface was prepared by a combination of sputtering and annealing at 1200 K and shows straight terraces separated mainly by double and four-fold steps. On the terraces rows were found, with a separation of about 25 /spl Aring/. Current versus voltage characteristics measured on this surface display a gap in the conductivity of about 2 eV. Results will be discussed considering the bulk Fe/sub 3/O/sub 4/ structure. >

Magneto-optical Faraday effect probed in a scanning tunneling microscope

Semiconductor tips are used as local photodetectors in a scanning tunneling microscope. We demonstrate that this configuration is sensitive to small light intensity variations, as supported by a simple model. The principle is applied to the detection of Faraday ellipticity of a Pt/Co multilayer sample. The outlook of this new technique in magneto-optical imaging is briefly discussed. >

Photo-assisted tunneling at ferromagnet/semiconductor interfaces

We have measured the polarization-dependent photoresponse of ferromagnet-insulator-(III–V) semiconductor thin film tunnel structures as a function of wavelength. When the structures have no interfacial barrier, we find that the response agrees well with calculations of magneto-optical transmission through the magnetic overlayer. However, when a tunnel barrier is present and excitation nearly resonant with the semiconductor bandgap, we observe significant deviations from the magneto-optical effects. These deviations are attributed to spin-dependent electron transmission from the III–V semiconductor acting as a spin-polarized source of tunneling electrons.

Photosensitive Semiconductor Tips in a Scanning Tunneling Microscope

The photosensitivity of GaAs tips is studied in a scanning tunneling microscope. Measurements of surface photovoltage and zero-bias photocurrent versus incident light power are presented together with a simple theoretical model. It is shown that these tips can be used for measurement of local sample magnetization through the magneto-optical Faraday effect.