409 research outputs found
Offset fields in perpendicularly magnetized tunnel junctions
We study the offset fields affecting the free layer of perpendicularly
magnetized tunnel junctions. In extended films, the free layer offset field
results from interlayer exchange coupling with the reference layer through the
MgO tunnel oxide. The free layer offset field is thus accompanied with a shift
of the free layer and reference layer ferromagnetic resonance frequencies. The
shifts depend on the mutual orientation of the two magnetizations. The offset
field decreases with the resistance area product of the tunnel oxide.
Patterning the tunnel junction into an STT-MRAM disk-shaped cell changes
substantially the offset field, as the reduction of the lateral dimension comes
with the generation of stray fields by the reference and the hard layer. The
experimental offset field compares best with the spatial average of the sum of
these stray fields, thereby providing guidelines for the offset field
engineering.Comment: Special issue of J. Phys. D: Appl. Phys (2019) on STT-MRA
Gilbert damping of high anisotropy Co/Pt multilayers
Using broadband ferromagnetic resonance, we measure the damping parameter of
[Co(5 \r{A})/Pt(3 \r{A})] multilayers whose growth was optimized to
maximize the perpendicular anisotropy. Structural characterizations indicate
abrupt interfaces essentially free of intermixing despite the miscible
character of Co and Pt. Gilbert damping parameters as low as 0.021 can be
obtained despite a magneto-crystalline anisotropy as large as
. The inhomogeneous broadening accounts for part of the
ferromagnetic resonance linewidth, indicating some structural disorder leading
to a equivalent 20 mT of inhomogenity of the effective field. The unexpectedly
relatively low damping factor indicates that the presence of the Pt heavy metal
within the multilayer may not be detrimental to the damping provided that
intermixing is avoided at the Co/Pt interfaces
SOT-MRAM 300mm integration for low power and ultrafast embedded memories
We demonstrate for the first time full-scale integration of top-pinned
perpendicular MTJ on 300 mm wafer using CMOS-compatible processes for
spin-orbit torque (SOT)-MRAM architectures. We show that 62 nm devices with a
W-based SOT underlayer have very large endurance (> 5x10^10), sub-ns switching
time of 210 ps, and operate with power as low as 300 pJ.Comment: presented at VLSI2018 session C8-
Deposition and patterning of magnetic atom trap lattices in FePt films with periods down to 200 nm
Back-hopping in Spin-Transfer-Torque switching of perpendicularly magnetized tunnel junctions
We analyse the phenomenon of back-hopping in spin-torque induced switching of
the magnetization in perpendicularly magnetized tunnel junctions. The analysis
is based on single-shot time-resolved conductance measurements of the
pulse-induced back-hopping. Studying several material variants reveals that the
back-hopping is a feature of the nominally fixed system of the tunnel junction.
The back-hopping is found to proceed by two sequential switching events that
lead to a final state P' of conductance close to --but distinct from-- that of
the conventional parallel state. The P' state does not exist at remanence. It
generally relaxes to the conventional antiparallel state if the current is
removed. The P' state involves a switching of the sole spin-polarizing part of
the fixed layers. The analysis of literature indicates that back-hopping occurs
only when the spin-polarizing layer is too weakly coupled to the rest of the
fixed system, which justifies a posteriori the mitigation strategies of
back-hopping that were implemented empirically in spin-transfer-torque magnetic
random access memories.Comment: submitted to Phys Rev.
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