Non-Uniform Switching of the Perpendicular Magnetization in a Spin-Torque Magnetic Nanopillar Page: 4 of 12
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Circularly polanrcd
Top lead Iccirical Iu ses
Cu hI c
4 .1
free laner
(u2 4 tflsjl
t reference layer
Cu
Bottom lead
X-ray detector
FIG. 1. (Color Online) Schematic of the Scanning Transmission X-ray microscopy (STXM) experi-
ment performed on a [Co/Ni] based nanopillar spin valve. The pulse sequence (current versus time)
is shown on the right. Letters (a), (b), (d) and (f) represent, respectively, the STXM measurements
corresponding to the images shown in Fig. (2)
and bottom leads are respectively Ta/Cu (50 nm) and Cu(15nm)/Ta(3nm). The multi-
layer film was then patterned using electron beam lithography and ion etching to form
100 x300 nm2 nanopillars with an ellipsoidal shape. A last chemical etching step was per-
formed on the sample backside to open a 200 x 200 nm2 window in the Si wafer. The
spin-torque devices sit in the center of this window on a 300 nm thick Si3N4 membrane
chosen for its transparency to x-rays. The samples were finally mounted to custom printed
circuit board sample holders and wire-bonded to SMA connectors so that current pulses
could be injected.
In order to image the magnetization reversal process, the scanning transmission x-ray
microscope (STXM) available on beamline 11.0.2 at the Advanced Light Source (ALS) was
used. Images of the spatially resolved magnetic contrast with an time resolution of 70 ps
were obtained as described in2932. Beamline 11.0.2 is equipped with an elliptically polarized
undulator (EPU) capable of providing arbitrary circular or linear polarization. In our exper-
iment, the incident beam was parallel to the surface normal (as show in Fig. (1) and focused
by a zone plate with a 25 nm resolution. The photon energy is tuned to the characteristic
Ni L3 resonance edge. Note that Ni is present in both free and reference layer but 2.5 times
more in quantity in the free layer. In the following, we consider the magnetic configuration4
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Bernstein, David. Non-Uniform Switching of the Perpendicular Magnetization in a Spin-Torque Magnetic Nanopillar, article, June 1, 2011; United States. (https://digital.library.unt.edu/ark:/67531/metadc830096/m1/4/: accessed March 28, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.