Gadolinium interaction inGdBa2Cu3Oycompounds

In ${\mathrm{Gd}}_x{\mathrm{Y}}_{1-x}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_y$ compounds having different oxygen contents ($6.0<y<\mathrm{}7.0\mathrm{}$), electron-spin-resonance spectra for gadolinium spins are observed. The linewidths are proportional to the square root of the gadolinium concentration, $x$. The gadolinium dipole-dipole interaction is dominant in these compounds. The temperature dependence of the spectra is measured down to 3.8 K. Below 20 K, a broadening of the linewidth is observed for nonsuperconducting $\mathrm{Gd}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_y$ compounds ($6.1<y<\mathrm{}6.4\mathrm{}$). The broadening has no oxygen concentration dependence. Different $g$ values are observed first in the compounds having different oxygen contents, $y$. The interactions among gadolinium ions are discussed.