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Materials Science Division |
HighlightsAnisotropic Superconductivity in MoGe-Permalloy HeterostructuresAnisotropic Superconductivity in MoGe-Permalloy Heterostructures Scientific Achievement Interaction of two (or more) systems
with strongly correlated electrons leads to a wealth of new physical
phenomena. Magnetism
and
superconductivity are not an exception as their mutual influence has
been
studied for decades. We
investigate
magneto-transport properties of magnetically coupled
superconductor-ferromagnet
heterostructures. We
show that the
superconducting order parameter of such system can be localized in
narrow
mesoscopic channels by virtue of the stray magnetic field emanating
from
domains of the ferromagnet. In
case of
magnetic stripe domain structures, this effect gives possibility to
create
superconducting nanowires without the need to employ nanoscale
lithography
technique. Permalloy is a ferromagnet which
forms well-ordered stripe magnetic domains at thicknesses higher than
certain
critical value. The
orientation of these
stripes adjusts parallel to the external in-plane magnetic field. Each stripe has
out-of-plane magnetization
that periodically changes sign inducing an in-plane anisotropy in the
superconducting order parameter of the adjacent MoGe film. In the case of
Ferromagnet/Superconductor/Ferromagnet trilayer it becomes important to
know
how magnetic domains of two Permalloy films align relatively each other. This alignment determines
the interference
picture of the stray magnetic field emanated from ferromagnetic layers
and
consequently influences the distribution of Cooper pair condensate in
the
superconductor. The
cooperation with the
Electron Microscopy Center has allowed us to verify our theoretical
estimates
and to prove that domains with identical direction of magnetization are
positioned under each other. This
became
possible by means of using the Focused Ion Beam machine which enabled
us to
image magnetic domain structure of both Permalloy layers in the hybrid. Significance Our collaboration with Electron Microscopy Center play an important role in the understanding of the physical processes taking place in superconductor/ferromagnet heterostructures. The characterization and imaging tools at EMC in conjunction with low temperature characterization methods at MSD allow for development of correct theoretical model describing the behavior of the system as in the state with domain walls parallel as perpendicular to the transport current. In the case when domain stripes are parallel to the transport current we demonstrate that the latter one flows through superconducting channels. The comprehension of the mutual influence of superconductor and ferromagnet in the hybrids gives one the possibility to engineer system with desirable microscopic and macroscopic properties. Relevant publication: Phys. Rev. B 77, 180506 (2008); Appl. Phys. Lett. 93, 072510 (2008); J. Phys. Conf. Ser. in press (2008). Performers 
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