Influence of hydrogen on the magnetic and electrical properties of GdI2Hx (0?x?1)

We have studied the effect of hydrogen insertion in GdI₂ on its magnetic and electrical properties. The ferromagnetic layered metal GdI₂ reversibly absorbs hydrogen with the formation of GdI₂H_x which exhibits a range of homogeneity 0?x?1. These phases crystallize with the hexagonal MoS₂-type heavy atom arrangement. Variation of the hydrogen content is accompanied by a monotonic change in the lattice parameters, and a decreases from 4.074(1) to 4.023(1) Å whereas c increases from 15.050(5) to 15.394(5) Å for x=0-0.97. The molar volume passes through a maximum at x≈0.35. Magnetization and resistance measurements reveal a substantial change in the physical properties of GdI₂H_x as a function of the hydrogen content, particularly as x approaches a critical value of ∼1/3. The Curie temperature rapidly decreases with increasing hydrogen content, and the long-range magnetic ordering is destroyed for x>0.33. The phases GdI₂H_x with 0.42?x?0.69 exhibit characteristics of a spin-glass below the magnetic freezing temperatures T_f=24 and 3 K for x=0.42 and 0.69, respectively. The hydride halides GdI₂H_x (x>0.19) show thermally activated conduction, accompanied by a steep increase of the activation energy at x≈0.33. The anomalies observed can be understood by assuming an ordering of the hydrogen atoms for x=1/3 within each layer.