Critical behaviour of ZrZn 2

Abstract

The nature of the metallic state of the low temperature itinerant ferromagnet ZrZn 2 in the vicinity of a magnetic quantum phase transition has been studied in a series of susceptibility and resistivity measurements under high pressures. A pressure-temperature phase diagram has been constructed on the basis of the susceptibility data. The magnetic transition temperature is observed to follow T c 4 3 ∼ (p c − p) down to temperatures of order 1 K. No evidence for a first order transition was found at any pressure, but a clearly defined and moderately pressure-dependent maximum was observed in the susceptibility in the paramagnetic regime, i.e. for p > p c. The temperature dependence of the resistivity is found to differ from that of the conventional Fermi liquid model over a wide range of temperature and pressure. The shape of the phase diagram and the observed behaviour of the resistivity have been interpreted in terms of a quantum Ginzburg Landau model for the magnetic fluctuation spectrum.