Abstracts Book - IMRC 2018

• SF1-O004 Invited Talk
THE MARRIAGE OF FERROMAGNETISM AND
SUPERCONDUCTIVITY: A NEW TWIST
Samuel Bader 1
1 Argonne National Laboratory, Materials Science Division and Center for Nanoscale Materials,
United States.
Nanocomposite hybrid materials enable the creation and tailoring of new
properties known component materials. [1,2] This is especially interesting when
dealing with materials whose properties tend to be mutually exclusive, as in
ferromagnets (F) and superconductors (S). When superconductivity and
ferromagnetism co-exist, rather intriguing and even quite spectacular
properties can develop. Theory predicts long-coherence-length, spin-triplet
superconductivity at the F/S interface with an inhomogeneous magnetization
[3]. Magnetic non-collinearity is a crucial but not quantitatively controlled
parameter in most experiments inferring spin triplet superconductivity. In this
work, we use Nb, and an epitaxial exchange spring Py/Sm-Co bilayer with
uniaxial in-plane anisotropy in the Sm-Co layer [4]. Due to the interfacial
exchange coupling, a tunable non-collinear spin spiral can be achieved by
rotating the sample in fixed field. At a fixed temperature within the
superconducting transition, starting a collinear magnetic configuration, as the
spin spiral’s winding angle increases, the superconducting critical current first
increases, peaks, and then decreases. The twist to the story is that this
dependence is unanticipated. This tells us that there is new physics yet to
captured in F/S theories.
[1] Bader S. D. and Parkin S. S. P. (2010). Spintronics, in Annual Reviews of
Condensed Matter Physics 1, 71-88
[2] Bader S. D. (2006). Colloquium: Opportunities in Nanomagnetism, Rev. Mod.
Phys. 78, 1-15
[3] Bergeret F. S., Volkov A. F., and Efetov K. B. (2001). Long-range proximity
effects in superconductor-ferromagnet structures, Phys. Rev. Lett. 86, 4096
[4] Zhu L., Liu Y., Bergeret F. S., Pearson J. E., te Velthuis S. G. E., Bader S. D. and
Jiang J. S. (2013). Unanticipated proximity behavior in
ferromagnet/superconductor heterostructures with controlled magnetic noncollinearity,
Phys. Rev. Lett. 110, 177001