Magnetic and transport properties of single-grain R-Mg-Zn icosahedral quasicrystals [R=Y, (Y_1-xGd_x), (Y_1-xTb_x), Tb, Dy, Ho, and Er]

We report measurements of the dc magnetization, the low-field ac magnetic susceptibility, and the electrical resistivity of large (up to 0.5 cm³) single-grain samples of icosahedral R-Mg-Zn (R=Y, Tb, Dy, Ho, and Er). The dc magnetization and ac magnetic susceptibility data both indicate that icosahedral Tb-Mg-Zn and Dy-Mg-Zn undergo a transition to a spin-glass state at T_f=5.8 and 3.6 K, respectively, while low-temperature ac susceptibility measurements show that T_f=1.95 and 1.3 K for Ho-Mg-Zn and Er-Mg-Zn, respectively. For the series of solid solutions (Y_1-xTb_x)-Mg-Zn, the freezing temperature T_f varies approximately as x^2/3. The (Y_1-xGd_x)-Mg-Zn solid solutions have lower T_f values than (Y_1-xTb_x)-Mg-Zn for the same magnetic rare-earth concentrations (x), indicating that local moment anisotropy caused by crystalline electric-field effects plays a significant role in increasing T_f. On the other hand, angular-dependent studies show that the dc magnetization for T>T_f is isotropic within the experimental uncertainty. The electrical resistivity ρ(T) of the single-grain samples is only weakly temperature dependent, with a small, negative dρ/dT. Absolute values of the resistivity fall in the range between 150 and 200 μΩ cm, which is distinctly lower than the values previously reported for other thermodynamically stable icosahedral quasicrystals.