Plenarvorträge - DPG-Tagungen

Symposium X-RAY Magneto-Optics Dienstag
Fachsitzungen
– Hauptvorträge –
SYXM 1 X-Ray Magneto-Optics
Zeit: Dienstag 14:30–18:00 Raum: H1
Hauptvortrag SYXM 1.1 Di 14:30 H1
Magneto-optical polarisation spectroscopy with soft x-rays
— •Hans-Christoph Mertins 1 , Sergio Valencia 2 , Andreas
Gaupp 2 , Wolfgang Gudat 2 , and Peter Oppeneer 3 — 1 University
of Applied Sciences, Münster, Stegerwaldstr. 39, 48565 Steinfurt —
2 BESSY, Berlin, Germany — 3 IFW-Dresden, Germany
Among the x-ray magneto-optical spectroscopy techniques, the polarisation
analysis of light after its interaction with the material gaines
increasing importance since it reveals both, the intensity and the phase.
Thus it directly gives the complete magneto-optical constants, something
that is not possible with a single intensity measurement.
Polarisation effects appear when linearly polarized light interacts with
a sample that has a magnetization component parallel to the light propagation
direction k. Behind the sample the light polarisation plane is
rotated and the polarisation has changed to elliptical. This effect has been
observed in transmission (Faraday effect [1]) and recently in reflection (L-
MOKE [2]). Both effects are even in the magnetization M allowing for
investigations of ferromagnetic materials. Antiferromagnetic ordering can
be probed by second order effects by applying a perpendicular orientation
between k and M (Voigt effect [3]).
The applicability of these effects for the characterization of magnetic
materials and devices is demonstrated with x-ray rotation and ellipticity
spectra across the 3p and 2p edges of Mn, Fe, Co and Ni.
[1] J. Kunes et al., Phys. Rev. B 64, 174417 (2001)
[2] H.-Ch. Mertins et al., Phys. Rev. B, in press (2003)
[3] H.-Ch. Mertins et al., Phys. Rev. Lett. 87, 047401 (2001).
Hauptvortrag SYXM 1.2 Di 15:00 H1
Magnetization profiling by resonant magnetic x-ray reflectometry
— •G. Schütz, J. Geissler, and E. Goering — Max-Planck
Institut für Metallforschung, Stuttgart
The asymmetry ratio of resonant magnetic x-ray reflection shows a
strong variation with the angle of incidence. The maximum value of the
complex magnetic reflection profile is in the order of the corresponding
XMCD signal, from which the main magnetic contribution of the
absorptive scattering amplitude can be deduced while the dispersive
part is calculated via Kramers Kronig relations. If the correlation of
the XMCD effect to the atomic magnetic moment is known, the magnetization
depth profile can be deduced by an artificial slicing method
utilizing the Parratt algorithm [1]. For hard x-rays (e.g. L2,3 edges for 4f
or 5d elements) with scattering vector of less than one degree cross and
scalar products can be simplified. The application of this theoretical
model is much more complicated for soft x-rays and related to large
scattering angles. However, this energy range covers the L2,3 edges of 3d
transition elements, which exhibit large asymmetry ratios amounting to
50 % [2]. The potential of this method especially for technical relevant
GMR/TMR systems, whose magneto-electric properties can strongly
depend on the interphase morphogy, is demonstrated for a Pt/Co/Cu
trilayer. For this composition it was possible to determine the variation
of the magnetic interface depth profile for each layer reaching an
accuracy of about 10 % for Pt and Co with a depth resolution up to 0.1
nm. Even for the Cu component an estimation of the induced magnetic
moment at the Co-Cu interface is possible [3].
[1] J. Geissler et al., Phys. Rev. B 65, 020405 (2001)
[2] J. Geissler et al., Z. Metallkd. 93, 946 (2002)
[3] E. Goering et al., in preparation
Hauptvortrag SYXM 1.3 Di 15:30 H1
X-ray magneto-optics of lanthanide materials: principles and
applications — •José Emilio Prieto, Franziskus Heigl, Oleg
Krupin, Kristian Döbrich, Günter Kaindl, and Kai Starke —
Institut für Experimentalphysik, Freie Universität Berlin, Germany
Lanthanides are frequently employed in technical magnetic systems
to achieve high anisotropies. In contrast to transition metals, magnetic
moments are carried mainly by the localized 4f electrons, and their correlation
energies give rise to rich multiplet structures in optical excitation
spectra whenever the 4f shell is involved. This results in strong magnetic
dichroism in x-ray absorption and, due to the connection between real
and imaginary parts of the refractive index, also in large magneto-optical
effects in resonant reflectivity [1].
Soft x-ray magneto-optics is well suited to study magnetization
reversal processes in external magnetic fields. Yet in order to obtain
quantitative information on the magnetization from reflectivity data,
comparison with model calculations is required. Here we report on
recent progress in determining the soft x-ray magneto-optical constants
of lanthanides [2,3] and show examples of applying specular resonant
reflectivity to analyse the magnetization reversal of thin films and
exchange-coupled trilayer systems in an element specific way.
[1] K. Starke, F. Heigl, A. Vollmer, M. Weiss, G. Reichardt, and
G. Kaindl, Phys. Rev. Lett. 86, 3415 (2001)
[2] J. E. Prieto, F. Heigl, O. Krupin, G. Kaindl, and K. Starke, Phys.
Rev. B 66, 172408 (2002)
[3] J. E. Prieto, F. Heigl, O. Krupin, G. Kaindl, and K. Starke, Phys.
Rev. B 68, 134453 (2003)
Hauptvortrag SYXM 1.4 Di 16:00 H1
Resonant soft x-ray diffuse scattering from magnetic multilayers
— •Maurizio Sacchi 1 , Carlo Spezzani 1 , Renaud Delaunay 2 ,
and Coryn F. Hague 1,2 — 1 LURE, Centre Universitaire Paris Sud, Orsay,
France — 2 LCP–MR, Université P. et M. Curie, Paris, France
We have applied resonant diffuse scattering of polarized soft x-rays
to the investigation of the field dependent magnetic structure in Co/Cu
multilayers. At remanence, and for weak applied fields, Co layers break
up into magnetic domains with a high degree of AF coupling normal
to the stacked layers. We estimate the degree of AF coupling and the
average size of the AF domains as a function of the applied field.
The analysis of the domain size distribution, and of its correlation with
magnetoresistance, after a demagnetization process gives further evidence
that the remanent magnetic structure is influenced by the magnetic history
of the multilayer.
We have compared the field dependence of the sample resistance and of
the scattered intensity at various off-specular angles. Our results suggest
that at high fields non-negligible variations in the resistance may be due
to the persistence of small magnetically hard domains.
Hauptvortrag SYXM 1.5 Di 16:30 H1
Ab-initio calculations for adatoms and clusters on surfaces
— •Peter H. Dederichs — Institut für Festkörperforschung,
Forschungszentrum Jülich, D-52425 Juelich
Adatoms and small clusters on surfaces have a considerably lower coordination
number than in a bulk environment. Therefore one expects
that these nanostructures exhibit considerably larger spin and orbital
moments than in the bulk. Here we review a series of ab-initio results for
adatoms and small clusters on surfaces of the noble metals (Cu, Ag, Au,
Pt) and the ferromagnets Fe and Ni. The calculations were performed
within the density-functional formalism by using the KKR-Green’s function
method. On the noble metal surfaces, we find strongly enhanced
spin moments, and even small clusters of 4d atoms are magnetic. A much
stronger enhancement is found for the orbital moments and anisotropy
energies. Compared to this, the enhancement of the moments on the
surfaces of Fe and Ni are rather moderate, being a result of the much
stronger hybridisation of the adatoms with the substrate d states.