
surface alloys (Freyss et al. 1996) also including non-
collinear magnetic order (Sandratskii 1998)
The capability of this method was nicely confirmed
by experimental observation of the local magnetic
order in surface alloys by means of spin-polarized
scanning tunneling spectroscopy (Heinze et al. 2000).
See also: Monolayer Films: Magnetism; Density
Functional Theory: Magnetism; Itinerant Electron
Systems: Magnetism (Ferromagnetism); Multilayers:
Interlayer Coupling
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I. Mertig
Technische Universita
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Thin Film Magnetism: PEEM Studies
A Photoemission Electron Microscope (PEEM) im-
ages photo and/or secondary electrons, which are
generated at the surface of a solid sample by the ab-
sorption of x-ray or ultraviolet (UV) radiation. De-
pending on the wavelength of the radiation different
contrast mechanisms are present, providing informa-
tion on the elemental and chemical composition, and
the electronic and magnetic properties of the mate-
rial. Magnetic domain imaging is a major application
of the PEEM technique, exploiting strong x-ray mag-
netic dichroism effects, e.g., at the L edges of the
magnetic 3d transition metals (e.g., Cr, Mn, Fe, Co,
Ni). For a comparison with other domain imaging
techniques see Kerr Microscopy, Magnetic Materials:
Transmission Electron Microscopy, Magnetic Force
Microscopy, and references therein.
The PEEM technique stands out against other
magnetic imaging techniques through its surface sen-
sitivity and element specificity, making PEEM an
ideal tool for the investigation of ultra-thin magnetic
films, multi-layers, and alloys. In contrast to other
high resolution, magnetic imaging techniques, PEEM
is also sensitive to antiferromagnetic order. The spa-
tial resolution of PEEM for magnetic domain imag-
ing is typically about 50–100 nm, which positions
PEEM between Transmission Electron Microscopy
and optical techniques, such as Kerr Microscopy.
1. Photoemission Electron Microscopy
PEEM was first used in the 1930s and has since then
matured into an established surface science technique
(Sto
¨
hr et al. 1993, Tonner et al. 1995, Sto
¨
hr et al.
1998, Anders et al. 1999). PEEM is closely related to
the Low Energy Electron Microscope (LEEM) and
the Spin-polarized Low-energy Electron Microscope
(SPLEEM), which were pioneered by Bauer (1994)
and Duden and Bauer (1998). All three techniques
utilize low-energy electrons to form an image repre-
senting physical properties of the sample surface.
LEEM and SPLEEM image diffracted low-energy
electrons and thereby provide information on the
local crystallographic (LEEM) and magnetic
(SPLEEM) structure of the surface of a crystalline
sample. PEEM, in contrast, images electrons gener-
ated by photoionization and therefore is not limited
to the study of crystalline samples (see also Photo-
emission: Spin-polarized and Angle-resolved). As light
sources, UV gas discharge lamps, UV lasers, and
synchrotron radiation sources have been used. Syn-
chrotron radiation offers the important advantage of
tunability of the wavelength of the illumination,
thereby allowing a selection between various mech-
anisms of contrast. X-ray PEEM thus combines as-
pects of spectroscopic and microscopic methods and
is called a spectromicroscopy technique.
A typical PEEM setup using synchrotron radiation
from a bending magnet is shown in Fig. 1 (Anders
et al. 1999, Scholl et al. 2002). X rays pass through a
moveable aperture, which selects the polarization of
the radiation. A spherical grating monochromator
and an exit slit monochromatize and focus the beam
onto the sample. A schematic kinetic energy spectrum
of the emitted electrons after x-ray absorption is
shown in Fig. 2(a). Photoemission lines appear at
high kinetic energy, followed by a broad tail of sec-
ondary electrons which peak at low energies close
to the work function cut-off. PEEM microscopes
usually accept the total electron yield without prior
1229
Thin Film Magnetism: PEEM Studie s