Anomalous Variation of the Recoil‐Free Fraction of ¹⁵¹Eu Nucleus in Euba₂Cu₃O_7−x around the Superconducting Transition Temperature

Mössbauer spectra of the superconductor EuBa₂Cu₃O_7−x are measured at various temperatures (83 to 120 K) and the effective absorber thickness is calculated from the experimental spectra. The temperature variation of the recoil‐free fraction of the ¹⁵¹Eu nucleus in Euba₂Cu₃O_7−x is obtained. An anomaly in the temperature dependence of the recoil‐free fraction of the ¹⁵¹Eu nucleus in the superconductor EuBa₂Cu₃O_7−x is found around the superconducting transition temperature. This may provide evidence of softening of lattice vibrations about the Eu atom in the crystal in the normal state‐superconducting state transition process of the EuBaCuO system.