Electron Spin Resonance Investigation of the Conducting Dihydrides of Gadolinium and Gadolinium–Yttrium Alloys

Abstract

Electron spin resonance linewidths and g shifts have been obtained in the temperature range 100–300°K for the gadolinium f electrons in the systems MHx (1.90 < x < 2.46; M ≡ Gd, Gd0.71Y0.29, or Gd0.50Y0.50). The systems behave differently depending on whether x > xcor x < xc; xc = 2.12, 2.07, 1.91 forM ≡ Gd, Gd0.71Y0.29, and Gd0.50Y0.50, respectively. For x > xc the g shifts (relative to g for Gd in insulators) were ≈ + 0.01, independent of x and of temperature. These shifts are interpreted as the result of the exchange interaction − JS·s between the gadolinium f electrons and the s conduction electrons, indicating that hydrogen enters the lattice as H−. The g values are slightly temperature dependent for x <x c. The linewidth is proportional to the temperature, characteristic of the Korringa formula, above x = xc. Below x = xc the linewidth becomes temperature independent and increases with decreasing hydrogen content. This temperature independent broadening is linked with vacant tetrahedral interstices, normally occupied by hydrogens in the face-centered cubic metal lattice.