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

We have performed magnetization measurements at high magnetic fields of up to 53 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}el temperature $T_{\mathrm{N}}$ = 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$-axis). The magnetic phase diagram for the field along the [11$\bar{2}$0] direction is given. The magnetization curve shows a nonlinear increase at $H_m$ $\simeq$ 35 T in the paramagnetic state above $T_{\mathrm{N}}$ up to a characteristic temperature $T_{\chi \mathrm{m}\mathrm{a}\mathrm{x}}$ where the magnetic susceptibility or electrical resistivity shows a maximum value. This metamagnetic behavior of the magnetization at $H_m$ is discussed in comparison with the metamagnetic magnetism of the heavy-fermion superconductors UPt${}_3$, URu${}_2$Si${}_2$, and UPd${}_2$Al${}_3$. We have also carried out high-pressure resistivity measurement on U${}_2$Zn${}_{17}$ using a diamond anvil cell up to 8.7 GPa. Noble gas argon was used as a pressure-transmitting medium to ensure a good hydrostatic environment. The N'{e}el temperature $T_{\mathrm{N}}$ is almost pressure-independent up to 4.7 GPa and starts to increase in the higher-pressure region. The pressure dependences of the coefficient of the $T^2$ term in the electrical resistivity $A$, the antiferromagnetic gap $\mathrm{\Delta }$, and the characteristic temperature $T_{\rho \mathrm{m}\mathrm{a}\mathrm{x}}$ are discussed. It is found that the effect of pressure on the electronic states in U${}_2$Zn${}_{17}$ is weak compared with those in the other heavy fermion compounds.