Metal-insulator transition in layered manganites: ${(\mathrm{L}\mathrm{a}}_{1-z}{\mathrm{Nd}}_z{)}_{1.2}{\mathrm{Sr}}_{1.8}{\mathrm{Mn}}_2{\mathrm{O}}_7$

Lattice effects on the anisotropic magnetic and transport properties have been investigated for single crystals of (La${}_{1-z}$Nd${}_z{)}_{1.2}$Sr${}_{1.8}$Mn${}_2$O${}_7$ with a layered structure. The ferromagnetic transition temperature $T_C$ is suppressed from $T_C$=130 K for $z$=0.0 to 80 K for $z$=0.2, and eventually the transition disappears beyond $z$=0.4. From the significant change of the magnetic anisotropy, we have found that the suppression originates from the increasing $d_{{3z}^2-r^2}$ character in the occupied $e_g$ state due to the Jahn-Teller distortion of the MnO${}_6$ octahedra. Our observations indicate that the effects of chemical substitution are qualitatively different between the cubic and layered doped manganites.