A. Närmann

Surface magnetism studied by polarized light emission after He+ scattering

Abstract Surface magnetism is studied by means of an ion beam of low energy (2–15 keV) scattered off the surface under grazing incidence conditions. During the scattering, a small fraction of the ions is neutralized into excited states which decay subsequently by light emission. The circular polarization of the light emitted after the scattering event is related to the surface magnetization of the sample. We used a Fe(1 1 0) single crystal and a He + ion beam to study the circular polarization as a function of a number of parameters, such as primary energy, angle of incidence and azimuthal angle of the sample. The results are discussed in terms of the spin-filter model.

Spin-sensitive electron capture into excited states as a probe to investigate magnetic surfaces

In the neutralization process into an excited state during He+ scattering of magnetic surfaces the orientation off the spill of the captured electron can be extracted by analyzing the degree of circular polarization of the emitted light. In the grazing incidence mode the surface sensitivity is highest owing to the fact that the particles do not, penetrate into the target surface, but are scattered well above the uppermost atomic layer. Thus the electrons that neutralize the incoming ion originate from the topmost layer. This implies that the method is very well suited to investigate the properties of magnetic surfaces and multilayers. In this contribution we present new results concerning the surface sensitivity of the above method and experimentally show that thanes in the stale of magnetization of the surface are reflected in corresponding changes in the recorded signal

Circularly polarized photon emission spectroscopy of keV ions scattering off (un-)magnetized surfaces

Abstract To study the interaction of 2–15 keV He+ ions with (un-)magnetized surfaces we use the degree of circular polarization of photons emitted by the neutralized ions. The general features of the relation between circular polarization and the magnetic substate distributions of the neutralized particles are indicated. They provide the basis for discussing the results obtained for a magnetized Fe(110) single crystal. Different models are discussed and used to understand at least qualitatively the general trends in the measured data.

Emission of polarized light by slow ions after excitation near a magnetic surface

Abstract We investigation the emission of polarized light from slow (3–12 KeV) particles scattered off a magnetized Fe(110) surface for different transitions, energies and incident angles. Recently, a similar experiment has been performed for the grazing incident case at much higher energies [H. Winter, H. Hagedorn, R. Zimny, H. Nienhaus and J. Kirschner, Phys. Rev. Lett. 62 (1989) 296]. By changing the incident angle we can separate effects due to anisotropically distributed angular momenta from effects due to the polarization of surface electrons.

Structural and Magnetic Properties of Co-Cu Film Systems

Thin films of Co on Cu are studied with respect to structural and magnetic properties by means of STM, MOKE and spin sensitive electron capture from surfaces (ECS). Sub-monolayer coverages of Co have been deposited on vicinal Cu(lll) surfaces with steps oriented along (110). STM topographies revealed that on vicinal surfaces regular arrays of steps with {100} as well as with {111} minifacets can be prepared. As Co is deposited it aggregates on both types of surfaces at the steps. On the surfaces with the {100} facets the step array is rearranged into a configuration where double steps dominate. Along the {100} facets of the double steps the Co exists as one-dimensional structures. Magnetic properties, e.g. hysteresis loops, are measured for different Co thicknesses above one monolayer on low-indexed Cu(lll). The difference between the ECS and the MOKE hysteresis loops, respectively, afford insights into relations between bulk and surface magnetic properties.

Probing of magnetic surfaces with inherent monolayer sensitivity by ion scattering

Abstract When ions scatter off surfaces, some particles are neutralized into excited states that are subsequently de-excited by light emission. In case of magnetic surfaces the information about the spin of the captured electron might be accessed via the polarization of the emitted light. In the grazing incidence mode, the surface sensitivity is highest due to the fact that the particles do not penetrate into the target surface but are scattered well above the uppermost atomic layer. Thus the electrons that neutralize the incoming ion originate from the topmost layer. This implies that the method is very well suited to investigate the properties of magnetic surfaces and multilayer structures. We present data that show the inherent surface sensitivity of this method. By properly choosing the experimental parameters one also assures that the energy deposited by the projectiles in the surface is negligible as well as the number of sputtered particles. We also present the first hysteresis curves recorded with this method, thereby showing that the measured signal follows the magnetic state of the surface. In combination with its surface sensitivity this shows that ion beam scattering is very well suited to investigate not only the surfaces of magnetic materials but also (ultra-)thin films and multilayer systems.

Surface magnetism investigated by low energy ion scattering in the grazing incidence mode

When scattering ions off surfaces, some particles are neutralized into excited states that are subsequently de-excited by light emission. In the case of magnetic surfaces the information about the spin of the captured electron might be accessed via the polarization of the emitted light. In the grazing incidence mode the surface sensitivity is highest due to the fact that the particles do not penetrate into the target surface but are scattered well above the uppermost atomic layer. Thus the electrons that neutralize the incoming ion originate from the topmost layer. This implies that the method is very well suited for investigating the properties of magnetic surfaces and multilayers. We present a UHV setup that serves this purpose as well as some results obtained for magnetized Fe(110) surfaces.