Ferromagnetism and superconductivity are thought to compete in conventional superconductors, although in principle it is possible for any metal to become a superconductor in its non-magnetic state at a sufficiently low temperature. At pressures above 10 GPa, iron is known to transform to a non-magnetic structure and the possibility of superconductivity in this state has been predicted. Here we report that iron does indeed become superconducting at temperatures below 2 K at pressures between 15 and 30 GPa. The transition to the superconducting state is confirmed by both a drop in resistivity and observation of the Meissner effect.
A search for superconductivity of magnetic elemental metals is performed.
A successful discovery of the onset of superconductivity is reported in
the case of iron under pressure. By electrical resistance measurement,
a maximum value of the superconducting transition temperature
Tc of 2 K and the upper
critical magnetic field Hc
of 0.2 T are observed under pressure of 20 GPa where iron is in the crystallographic
hcp phase and non-magnetic. Further confirmation of the superconducting
transition of hcp iron was obtained by the detection of the diamagnetic signal due
to the Meissner effect in accordance with the results of the electrical resistance
measurements.
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