Magnetic Field and Pressure Phase Diagrams of Uranium Heavy-Fermion Compound U$_2$Zn$_{17}$

摘要

We have performed magnetization measurements at high magnetic fields of up to53 T on single crystals of a uranium heavy-fermion compound U$_2$Zn$_{17}$grown by the Bridgman method. In the antiferromagnetic state below the N\'{e}eltemperature $T_{\rm N}$ = 9.7 K, a metamagnetic transition is found at $H_c$$\simeq$ 32 T for the field along the [11$\bar{2}$0] direction ($a$-axis). Themagnetic phase diagram for the field along the [11$\bar{2}$0] direction isgiven. The magnetization curve shows a nonlinear increase at $H_m$ $\simeq$ 35T in the paramagnetic state above $T_{\rm N}$ up to a characteristictemperature $T_{{\chi}{\rm max}}$ where the magnetic susceptibility orelectrical resistivity shows a maximum value. This metamagnetic behavior of themagnetization at $H_m$ is discussed in comparison with the metamagneticmagnetism of the heavy-fermion superconductors UPt$_3$, URu$_2$Si$_2$, andUPd$_2$Al$_3$. We have also carried out high-pressure resistivity measurementon U$_2$Zn$_{17}$ using a diamond anvil cell up to 8.7 GPa. Noble gas argon wasused as a pressure-transmitting medium to ensure a good hydrostaticenvironment. The N\'{e}el temperature $T_{\rm N}$ is almostpressure-independent up to 4.7 GPa and starts to increase in thehigher-pressure region. The pressure dependences of the coefficient of the$T^2$ term in the electrical resistivity $A$, the antiferromagnetic gap$\Delta$, and the characteristic temperature $T_{{\rho}{\rm max}}$ arediscussed. It is found that the effect of pressure on the electronic states inU$_2$Zn$_{17}$ is weak compared with those in the other heavy fermioncompounds.