Heavy Quasiparticles in the Ferromagnetic SuperconductorZrZn2

We report a study of the de Haas–van Alphen effect in the normal state of the ferromagnetic superconductor ${\mathrm{Z}\mathrm{r}\mathrm{Z}\mathrm{n}}_2$. Our results are generally consistent with a linear muffin-tin orbital band structure which predicts four exchange-split Fermi surface sheets. Quasiparticle effective masses are enhanced by a factor of 4.9 implying a strong coupling to magnetic excitations or phonons. ${\mathrm{Z}\mathrm{r}\mathrm{Z}\mathrm{n}}_2$ is unique among metallic ferromagnets in that it has a very large density of states in the ferromagnetic phase.