​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 been observed. 

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 is formed, 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 a NiBi3 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) 

DOI: 10.1103/PhysRevResearch.2.013270