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 GdI2Hx which exhibits a range of homogeneity image. 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 image decreases from 4.074(1) to 4.023(1) Å whereas c increases from 15.050(5) to 15.394(5) Å for image. The molar volume passes through a maximum at image. Magnetization and resistance measurements reveal a substantial change in the physical properties of GdI2Hx as a function of the hydrogen content, particularly as image 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 image. The phases GdI2Hx with image exhibit characteristics of a spin-glass below the magnetic freezing temperatures image and 3 K for image and 0.69, respectively. The hydride halides GdI2Hx (image) show thermally activated conduction, accompanied by a steep increase of the activation energy at image. The anomalies observed can be understood by assuming an ordering of the hydrogen atoms for image within each layer.