Avoided ferromagnetic quantum critical point in CeZn

Cubic CeZn shows a structural phase transition under pressure and it modifies the ground state from an antiferromagnetic (AFM) state to a ferromagnetic (FM) state. To investigate how the FM state terminates at a quantum phase transition, we measured the electrical resistivity under pressure for a single-crystal CeZn. The transition temperature into the FM state decreases monotonously with increasing pressure, accompanied by the pronounced Kondo effect, but a drastic change in the field response occurs before the ordered phase terminates. This result suggests that the FM quantum critical point is avoided by the appearance of an AFM-like state.

Figure 1

Pressure-temperature phase diagram of CeZn, which is obtained in this study. (a) $0<T<300$ K, (b) $0<T<20$ K. The AFM phase at ambient pressure changes into the FM phase through the cubic to tetragonal structural phase transition. The magnetically ordered state terminates at $P_c\sim 3$ GPa. The metamagneticlike transitions appear in the pressure region, where the transition temperatures are indicated by the closed triangles. They suggest that the FM state changes into an AFM-like state just before a QCP is reached.

Figure 2

Temperature dependence of the electrical resistivity for CeZn. (a),(b) $P<2.5$ GPa; (c),(d) $P>2.5$ GPa; and (e) the lower temperature part down to 0.4 K. The AFM transition changes into the FM transition in the tetragonal phase below $T_S$. The magnetically ordered state vanishes at $\sim 3$ GPa. In the PM state, two local maxima denoted as $T_{\max 1}$ and $T_{\max 2}$ appear, and another characteristic temperature $T^{*}$ is seen above $\sim 3$ GPa.

Figure 3

(a)–(e) Temperature dependence of the resistivity under magnetic fields. At 1.25 and 2.05 GPa, the transition is changed into crossover as expected for an FM transition. Above 2.1 GPa, the transition temperatures decrease under magnetic fields, suggesting that the ordered phase is AFM-like. (c) and (d) show that the field-direction dependence is small at 2.13 GPa. Inset of (e) and (f): Corresponding metamagneticlike transition appears in the field sweep of resistivity above 2.1 GPa, and they seem to reach 0 T at approximately 2.82 GPa. (g) The magnetic-field-temperature phase diagram of CeZn. The points for $j\parallel H$ at 2.13 GPa are shown by opened triangles.