Quantum phase transitions in the itinerant ferromagnet ZrZn2

We report a study of the pressure p, temperature T and magnetic field B phase diagram of ZrZn2, the most promising material to exhibit ferromagnetic quantum criticality. We find that the ordered ferromagnetic moment disappears discontinuously at pc=16.5kbar. Thus, a tricritical point separates a line of first-order ferromagnetic transitions from second-order (continuous) transitions at higher temperature. We also identify two lines of transitions of the magnetization isotherms up to 12T in the p-T plane where the derivative of the magnetization changes rapidly