Conventional theory about superconductors requiring pairs of electrons with their spins
pointing in opposite directions meant that superconductivity and ferromagnetism were
previously thought to not be able to co-exist within the same material. However, in samples of
bilayers of nickel and bismuth, despite the ferromagnetic nickel a superconducting state had
A group of researchers from the University of Leeds used
polarized neutron reflectometry on Polref alongside SQUID
magnetometry and X-ray diffraction in the ISIS materials
characterisation lab, to measure changes in Bi/Ni samples
to determine the cause of this surprise superconductivity.
Their results, published in Physical Review Research, show
that even under ambient conditions a layer of NiBi3
and that this is the source of the superconductivity.
When freshly prepared, their layered samples were nonsuperconducting. However, when left at room temperature
for several days, or heated up to 50°C, the layers mix to form
layer. This shows the importance of storage conditions
to maintain the integrity of Ni/Bi layers, but also opens up
possibilities for both ferromagnetism and superconductivity
to be present in the same system.
Related publication: “Origin of superconductivity at nickel-bismuth interfaces.” Phys. Rev. Research, 2, 013270 (2020)