Effect of Ga substitution on the superconducting properties of the electron-doped system: Nd-Ce-Cu-O

We are reporting on results of dc magnetization measurements of the new electron-doped ${\mathrm{Nd}}_{2\mathrm{-}\mathrm{x}}$ ${\mathrm{Ce}}_{\mathrm{x}}$ ${\mathrm{Cu}}_{1\mathrm{-}\mathit{y}}$ ${\mathrm{Ga}}_{\mathit{y}}$ ${\mathrm{O}}_4$ superconductors. The effect of ${\mathrm{Ga}}^{3+}$ on $T_c$ is similar to that of ${\mathrm{Ce}}^{4+}$, although the extra electron of the former comes from the Cu-O planes. For example, for x=0.12 the undoped compound (y=0) is not superconducting; but by the addition of Ga (y=0.03), the material becomes superconducting at $T_c$=20 K, and the Meissner fraction and the critical current density are improved compared to ${\mathrm{Nd}}_{1.85}$ ${\mathrm{Ce}}_{0.15}$ ${\mathrm{CuO}}_4$. The irreversibility line $T_{\mathrm{irr}\left(\mathrm{H}\right)}$ for doped and undoped samples scales with the applied field as $H^p$, with p≃0.6, but for the Ga-doped sample it is pushed to higher temperatures.