Studying Nanoscale Magnetism and its Dynamics with Soft X-ray Microscopy Page: 1 of 6
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Studying nanoscale magnetism and its dynamics
with soft X-ray microscopy
Peter Fischer, Member, IEEE
Abstract-Magnetic soft X-ray microscopy allows for imaging
magnetic structures at a spatial resolution down to 15nm and a
time resolution in the sub-100ps regime. Inherent elemental
specificity can be used to image the magnetic response of
individual components such as layers in multilayered systems.
This review highlights current achievements and discusses the
future potential of magnetic soft X-ray microscopy at fsec X-ray
sources where snapshot images of ultrafast spin dynamics with a
spatial resolution below 10nm will become feasible.
Index Terms-Magnetic soft X-ray microscopy, magnetization
reversal, ultrafast spin dynamics, X-ray optics.
T HE magnetic properties of condensed matter is currently
one of most attractive research areas in solid state physics
both for fundamental and applied reasons .
Research of magnetism in low dimensions has led to
important fundamental discoveries, such as the interlayer
exchange coupling and the Giant Magnetoresistnace (GMR)
effect ,, which is now commonly used e.g. in read head
technologies. Solid state magnetism is also a prototype
example for the current transition in the way scientific research
is performed, i.e. the classical method of observation and
interpretation of physical phenomena is extended by the
capability and the desire to functionalize and control
magnetism down to fundamental length and time scales and
also to create novel materials such as multiferroics, which
envision revolutionary ways to tailor magnetism.
Recent achievements in state-of-the-art synthesis
capabilities, theoretical modeling and the availability of
analytical tools have contributed that magnetism has become
one of the most important branches in nanosciences with
numerous technological applications.
While fundamental length scales, such as magnetic
exchange length in magnetism, which are in the sub-10nm
regime can be approached to a large extent both
experimentally and theoretically with a variety of techniques,
the corresponding fundamental time scales down to the fs
Manuscript received October 25, 2007. This work was supported by the
Director, Office of Science, Office of Basic Energy Sciences, Materials
Sciences and Engineering Division, of the U.S. Department of Energy under
Contract No. DE-AC02-05-CH1 1231.
P.aFischer is with the E.O. Lawrence Berkeley National Laboratory, Center
for X-ray Optics, Berkeley, CA 94720 USA, (phone: 510-486-7052; fax: 510-
486-4550; e-mail: PJFischer@ lbl.gov).
regime can be approached by means of optical laser techniques
, but unfortunately with a limited spatial resolution.
The ultimate question, how magnetism behaves when both
the fundamental magnetic length and time scales will be
approached cannot be addressed today. A thorough
understanding of e.g. the nature and origin of the exchange
interaction is therefore still missing.
Magnetic microscopies have largely contributed to the
current level of understanding of magnetic phenomena. Spin
polarized Scanning tunneling microscopy provides static
images with almost atomic spatial resolution . On the other
hand time resolved Kerr microscopy using the magneto-optical
Kerr effect images with a time resolution down to fs regime,
however, as mentioned above with an inherent diffraction
limited spatial resolution in the sub-micrometer range only.
Furthermore, none of these techniques is able to distinguish the
magnetic response from individual components in
multicomponent novel materials, which is of paramount
interest in the development of novel materials.
The grand challenge is therefore to develop a magnetic
microscopy technique that allows for both a sub-10nm spatial
resolution with elemental specificity and, at the same time a
fsec time resolution with the capability to take instantaneous
snapshot images of thus ultrafast spin dynamics.
This review describes the potential of magnetic soft X-ray
microcopy, which combines X-ray magnetic circular dichroism
as element specific contrast with a high spatial resolution due
to Fresnel zone plates used as imaging X-ray optical elements.
Using the inherent time structure of current third generation
synchrotron sources a sub-100ps time resolution can be
achieved and with new fsec X-ray sources which will become
available in the near future, the time resolution can be
extended into the fsec regime.
II. EXPERIMENTAL DETAILS
A. Fresnel zone plate optics
The fact that the refractive index of soft X-rays is close to
unity, has prevented the use of soft X-ray microscopes for
almost 80 years after the discovery of X-rays by W.C.
Roentgen in 1895.
Fresnel zone plates (FZP), which are now used in X-ray
microscope, are circular gratings with a radially increasing line
density. These are diffractive elements where the focal length
depends on the wavelength of the X-rays. High quality FZP X-
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Mccall, Monnikue M & Fischer, Peter. Studying Nanoscale Magnetism and its Dynamics with Soft X-ray Microscopy, article, May 1, 2008; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc896098/m1/1/: accessed March 20, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.