Magnetic Cluster States in Nanostructured Materials Page: 3 of 6
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Figure 1: a) STEM image of Gd80Fe20 shows the EXAFS data from our previous run
path of the EDX analysis b) Gd and Fe at the APS have been analyzed and
concentrations along the arrow. the disorder parameters extracted for
the melt-spun samples. This analysis
has been complicated because the
io sE e samples are two-phase, but we now
90 o Gd have results in which we are
80 confident. Figure 1 shows STEM
70 analysis, completed at Oak Ridge
60 National Laboratory, of the two-
so phase nature of the sample. Figure 2
40 " shows the raw XAFS data.
30 -
20 . . " . " These systems show interesting
10 . magnetic behavior that appears to be
0 . . well-described by the random
so 40 30 20 10 o anisotropy model, surprisingly, even
position (nm) in samples where the Gd grains are
more than 100 nm in size. We have
succeeded in making a series of samples of varying Fe concentration in which the Gd
crystallite size is constant and only the size of the grain boundary regions changes as the
volume fraction of crystalline material changes.
We have shown that the behavior of the amorphous phase in the grain boundary region is
very different from bulk amorphous GdFe of comparable composition and believe the
difference is in pinning at surfaces and interfaces.
The coercivity exhibits an unusual behavior in that it decreases as the Gd grains order,
shows a hump, and then increases again, as is shown in Figure 4. This behavior can be
explained in terms of increasing anisotropy that decouples the grains as the temperature
decreases. This behavior is cluster-glass-like because some of the important signatures of
cluster glasses, like a sharp increase in the coercivity below the peak in the ZFC
magnetization, are not present.
We have taken the Gd-Fe system as far as we can; at this point, we need to focus on
systems that are single phase to make the atomic-scale disorder parameterization
possible.
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Leslie-Pelecky, Diandra. Magnetic Cluster States in Nanostructured Materials, report, June 13, 2008; United States. (https://digital.library.unt.edu/ark:/67531/metadc893796/m1/3/: accessed March 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.