Quantum Phase Transitions in the Itinerant FerromagnetZrZn2

Abstract

We report a study of the ferromagnetism of ${\mathrm{Z}\mathrm{r}\mathrm{Z}\mathrm{n}}_2$, the most promising material to exhibit ferromagnetic quantum criticality, at low temperatures $T$ as a function of pressure $p$. We find that the ordered ferromagnetic moment disappears discontinuously at $p_c=16.5\mathrm{k}\mathrm{b}\mathrm{a}\mathrm{r}$. 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 12 T in the $p\mathrm{\text{−}}T$ plane where the derivative of the magnetization changes rapidly. These quantum phase transitions (QPT) establish a high sensitivity to local minima in the free energy in ${\mathrm{Z}\mathrm{r}\mathrm{Z}\mathrm{n}}_2$, thus strongly suggesting that QPT in itinerant ferromagnets are always first order.