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A brief review will be given of the properties of superconducting ferromagnets, including UGe2, URhGe and UCoGe, demonstrating that superconductivity occurs in coincidence with a proximity to magnetic quantum critical points. Although structural similarities exist between the above materials, they have different magnetic and critical field anisotropies linked with different types of quantum critical point. What key features do these materials then share that stabilizes non-conventional superconductivity relative to good metallurgical samples of weakly ferromagnetic d-metals?
For UGe2 neutron scattering has revealed the damping of critical magnetic fluctuations to be different from that usually considered in the theory of weak d-metal magnetism (Huxley et al PRL91, 207201 (2003)). An extra source of damping is observed that is plausibly a direct consequence of strong spin-orbit interactions. This source of damping might play an important role in shaping the electronic properties and promoting superconductivity in the above systems and is observed to be much weaker in d-metal magnets. |
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