Magnetic properties of Eu-dopedLa2−xSrxCuO4studied by ESR

By analyzing electron spin resonance spectra of Gd spin probes in ${\mathrm{La}}_{2-x-y}{\mathrm{Eu}}_y{\mathrm{Sr}}_x{\mathrm{CuO}}_4,$ we find that in the low temperature tetragonal phase the frequency of the spin fluctuations ${\omega }_{\mathrm{sf}}$ of Cu ions considerably slows down in the samples with strongly suppressed superconductivity (Sr contents $x<\mathrm{}0.17\mathrm{}$). The effect is especially pronounced for $x$ close to $1/8.$ However, for the samples with Sr concentration $x\gtrsim 0.17$ the specific features of the spin dynamics of the low temperature structural phase almost vanish, whereas fully developed superconductivity reappears.