•C. Pfleiderer¹, M. Uhlarz¹, R. Vollmer¹, H. v. Löhneysen^1,2, S. M. Hayden³, G. G. Lonzarich⁴, A. D. Huxely⁵ und J. Flouquet^5
5DRFMC-SPSMS, CEA Grenoble, F-38054 Grenoble Cedex 9, France
¹Physikalisches Institut, Universität Karlsruhe, D-76128 Karlsruhe, Germany
²Institut für Festkörperphysik, Forschungszentrum Karlsruhe, D-76021 Karlsruhe, Germany
³H. H. Wills Physics Laboratory, Bristol BS8 1TL, UK
⁴Cavendish Laboratory, Cambridge CB3 0HE, UK

Itinerant ferromagnetism and superconductivity were long believed to represent incompatible forms of electronic order. The recent observation of superconductivity in the ferromagnetic state of UGe₂ [1], ZrZn₂ [2] and URhGe [3], on the other hand, contradicts the traditional view and suggests that their coexistence may well be a wide spread phenomenon. We review the superconducting and ferromagnetic phase diagrams and consider salient features of the magnetisation of ZrZn₂ and UGe₂ that are consistent with an abundance of nearly critical longitudinal spin fluctuations. These characteristics of the bulk magnetisation, when taken together with recent elastic neutron scattering experiments on UGe₂, suggest ferromagnetically mediated equal spin pairing.

[1] S. S. Saxena et al., Nature 406 (2000) 587.

[2] C. Pfleiderer et al., Nature 412 (2001) 58.

[3] D. Aoki et al., Nature 413 (2001) 613.