Spin fluctuations and the magnetic phase diagram of ZrZn2

The magnetic properties of the weak itinerant ferromagnet ZrZn2 are analyzed using Landau theory based on a comparison of density-functional calculations and experimental data as a function of field and pressure. We find that the magnetic properties are strongly affected by the nearby quantum critical point, even at zero pressure; local-density approximation LDA calculations neglecting quantum critical spin fluctuations overestimate the magnetization by a factor of approximate to3. Using renormalized Landau theory, we extract pressure dependence of the fluctuation amplitude. It appears that a simple scaling based on the fluctuation-dissipation theorem provides a good description of this pressure dependence.