Using
a photoelectron emission microscope as a laterally resolving detector for
x-ray magnetic circular dichroism (XMCD) spectroscopy,
local absorption spectra with microscopic resolution can be obtained. These
can be analyzed by the so-called sum rules to extract quantitative information
about spin and orbital magnetic moments.
The
images show the result of such a microspectroscopic study of a Co/Ni crossed
wedge on Cu(001). The Ni thickness increases from left to right, as indicated
at the top axes, the Co overlayer thickness from bottom to top, as indicated
at the right axes.
The
left hand side shows a microscopic image of the distribution of the Ni spin
moment, projected onto the light incidence direction (from bottom to top).
On the right hand side, the corresponding distribution of the Ni orbital
moment is shown. The legends at the bottom of each figure explain the color
code used. 76800 separate XMCD spectra, one for each image pixel, have been
analyzed to construct these images.
The dotted line in the images marks a spin reorientation transition in the bilayer. It
separates a region with out-of-plane magnetization in the lower part of the
images from a region with in-plane magnetization in the upper part. This
spin reorientation transition occurs as a function of both the Ni and Co
thicknesses.
An
analysis of the orbital to spin moment ratio as a function of lateral distance
from the spin reorientation line is shown in the next figure. The data points
were obtained by averaging along lines of one image pixel width, parallel
to the spin reorientation transition. The left hand side (negative distances,
red) corresponds to the upper part of the images, where in-plane magnetization
is present, the right hand side (positive distances, blue) to the lower part
of the images, where out-of-plane magnetization is
present. A distinct change in the ratio of orbital to spin
moment across the spin reorientation transition is clearly seen. It is attributed
to the magnetic anisotropy of the Ni layer, which is forced along its hard
in-plane directions by the presence of the Co overlayer in the top part of
the images.
This correlation between magnetic anisotropy and orbital magnetic moment makes XMCD microspectroscopy a powerful tool for the microscopic element-resolved investigation of magnetic anisotropies.
These studies were
performed at SPring-8 in Japan
in collaboration with S. Imada and S. Suga,
Osaka University.
Publication:
Physical
Review B 62, 3824 (2000).