Quantum criticality puzzle of ZrZn2

Abstract The ferromagnetic ordering temperature TC of single crystals of ZrZn2 decreases linearly with hydrostatic pressure and suggests the existence of a quantum critical point at p c ≈2.1 GPa . We report the magnetization of single crystal ZrZn2 at temperatures down to 1.5 K and magnetic field up to 12 T as function of pressure up to pc. We observe striking qualitative differences of the magnetic isotherms at ambient pressure as function of temperature as compared with the variation as function of pressure at low temperature. The deviations may suggest a break-down of the traditional weak-coupling approach to itinerant-electron quantum criticality.