Artificially structured magnetic materials. Technical progress report, October 1, 1993--September 30, 1994 Page: 4 of 9
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where EB are the Bragg energies,
Vo is the inner potential, 0 is
the angle of incidence, n the
order of the peak, and d the out-
of-plane lattice constant. The
energies and distances are given
in Hartrees, 1h = 27.18 eV, and
Bohrs, 1b = 0.529 A,
respectively. The angle of
incidence of the electron beam
was -7 degrees in the <11-2>
azimuth. We have measured
the inner potential shift for bulk
Co and bulk Cu to be 7.7 eV
and 8.5 eV, respectively. It
should be noted that we do not
know how the inner potential VO
varies as Cu is deposited.
However, because the two bulk
values are nearly the same, we
Figure 3 Change in average perpendicular lattice
spacings determined from shifts in lowest energy peak
locations in Fig. 2. The curve is a calculation discussed
used their average (8.1 eV) in all of our calculations. This causes only a small uncertainty in
our determined lattice spacings and is included in the error estimates.
From the shifts in the Bragg peaks upon coverage we can calculate changes in the
average out-of-plane lattice spacing according to equation (1), and which are shown as the
circles in Figure 3. Here we have used the lowest energy peak at 137 eV which is the most
surface sensitive with a mean sampling depth of only - 3 A. The mean free path of LEED
electrons at 137 eV is roughly 6 A. However, in a reflection-diffraction experiment in which
a monoenergetic beam must enter and exit the crystal, the mean sampling depth is half the
value of the mean free path. We have also calculated the coverage dependence of the
average lattice constant that would be expected if both the Co and Cu remain at their bulk
spacings. This average spacing is calculated using depth dependent weighting factors
derived assuming an exponential decay of the LEED electrons with a probing depth of 3 A.
The calculated solid curve in Figure 2 is in good agreement with the measured data
indicating that, to within our uncertainty, Cu grows at its bulk perpendicular lattice constant
on the Co surface. We see no evidence of any abrupt structural changes of greater than - 0.6
% at - 1 atomic layer coverage that would correlate with our observed peak in the anisotropy
at this coverage.
We have also taken LEED I-V spectra of the specular beam for Au and Pd overlayers
on Co. Both materials show strong multiple scattering where the peaks do not correspond to
Bragg peaks and therefore the above simple analysis cannot be applied.
D. Effect of an Insulating Overlayer
In order to further clarify the role of electronic interactions in the interface anisotropy,
we have measured the influence of an insulating overlayer, MgO on the perpendicular
magnetic properties. For the noble metals Ag, Au and Cu, for which we observe the
anomalous anisotropy behavior near 1 atomic layer coverage, there is also a hybridization
between the ferromagnetic metal and the overlayer electronic states. In the case of an
insulating MgO overlayer this electronic interaction between the ferromagnetic material and
overlayer is extremely weak. Therefore, one would not expect significant changes in
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Falco, C.M. & Engle, B.N. Artificially structured magnetic materials. Technical progress report, October 1, 1993--September 30, 1994, report, February 1, 1996; United States. (digital.library.unt.edu/ark:/67531/metadc671288/m1/4/: accessed September 25, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.