Mwj Menno Prins

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.

Optical second harmonic generation study of interface magnetism

The presence of a magnetization appears to have a strong effect on the optical second harmonic generation from Co/Au interfaces. The origin of this observation and its relevance for probing interface magnetism will be discussed.

Magnetization-induced optical second-harmonic generation from magnetic multilayers

Abstract The optical second-harmonic intensity generated by magnetic multilayers appears to depend strongly on the magnetization. Combining interface and magnetic sensitivity, magnetization-induced optical second-harmonic generation provides a unique tool to study magnetic interface properties. The underlying theoretical analysis is given and illustrated with an example and experiments on Co/Au multilayers.

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.

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.

Nonlinear and linear Kerr studies of Co/Cu multilayers

Magnetization induced optical second harmonic generation (MSHG) in combination with the magneto-optical Kerr effect (MOKE) was used to study thin Co films and Cu/Co multilayers of thicknesses between 1 and 20 monolayers (ML) grown on a Cu(001) substrate. From the different dependence of MSHG and MOKE on Co film thickness we get direct information about the interface sensitivity of MSHG. Modifying the vacuum/Co interface by gas adsorption yields the relative contributions of the vacuum/Co and the Co/Cu(001)-substrate interfaces. Both MSHG and MOKE data can be accurately described by a multiple reflection model.

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.

Modulated Photodetection with Semiconductor Tips in a Scanning Tunneling Microscope

We report on the detection of modulated light power irradiated into the tunnel junction of a scanning tunneling microscope. When semiconductor tips are used we can distinguish three contributions to the measured current: photocurrent due to electron-hole pair generation at the apex of the tip, a contribution of thermal tip-sample distance modulation, and a displacement current due to the surface photovoltage that develops on the tip surface. Using a simple model we can understand the phases of the detected signals with respect to the photoexcitation, and extract values for several capacitances and conductances involved in the tunnel junction. This is relevant for applications of high-frequency photoexcitation in scanned probe microscopies.