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Exchange anisotropy, engineered
coercivity and spin transport in atomically engineered
L10 heterostructures
Funding: Department of Energy, Basic Energy
Sciences (07/15/06 -07/14/10)
Abstract:
We are investigating some of the scientific and technically
challenging issues in thin film magnetism focusing
on epitaxially grown layers of specific L10 ordered,
intermetallic, heterostructures with well-controlled
crystallography and interface structure. Specifically,
we are addressing antiferromagnetic/ferromagnetic
systems, exhibiting exchange bias (EB) in both in-plane
(MnPd/Fe) and perpendicular (IrMn/(Co/Pt)n) geometries,
and ferromagnetic/ferrimagnetic (Co/Y3Fe5O12) bilayers
with strong interlayer exchange coupling and exhibiting
spin reorientation transitions. In the former case,
the work includes experimental and theoretical studies
to gain more fundamental insight into the origin and
magnitude of EB, as well as to address important aspects
of EB such as the asymmetry in the magnetic reversal
mechanism, the role of interfacial structure, including
compensated or uncompensated spins, AF domains and
competing anisotropies. Size effects, particularly
in structures with lateral dimension of the order
of their domain sizes, are studied by soft lithography/patterning,
and their time/temperature behavior by studies of
magnetic viscosity, anomalous Hall effect and ultra
fast magnetometry. These fundamental magnetic studies
also determine the distribution of anisotropies, long-term
thermal stability, high precessional switching and
magnetic damping. In the latter case of the metal/oxide
heterostructures, the domain structure of the metal
is carefully modulated by that of the underlying oxide,
opening the possibility of carrying out novel experiments
to study spin-dependent domain-wall scattering and
quantify domain wall resistance in mesoscopic geometries.
Ongoing work, utilizing state-of-the-art characterization
methods to address the critical role of all aspects
of the microstructure, at relevant length scales,
in determining these specific magnetic properties,
includes domain imaging by photoemission electron
microscopy (PEEM), element-specific X-ray magnetic
reflectivity and x-ray resonant scattering at the
ALS and BESSE II. Collaborative work with Prof. R.
Stamps (UWA) in modeling and analysis of slow-dynamics,
using an inductive ferromagnetic resonance technique,
as well as efforts to study spin-transfer torque in
these perpendicular anisotropy systems, including
a novel fabrication technique, has also been initiated.
The ultimate goal of this research is to gain a deeper
understanding of the range of related magnetic phenomena
and establish pathways for potential technological
applications of these thin film and patterned heterostructures.
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