Nd2Ni2MgH8 hydride: Synthesis, structure and magnetic properties

Hydrogen interaction with intermetallic compound Nd2Ni2Mg crystallizing in the tetragonal Mo2FeB2 type of structure leads to the formation of hydride/deuteride containing 7.4-8 H(D)/f.u. Hydrogen absorption is accompanied by a monoclinic deformation of the unit cell with the crystal structure data refined from Synchrotron XRD (Sp. gr. P21/c; a = 11.60733(5) Å; b = 7.66057(3) Å; c = 11.78743(5) Å, β = 92.4126(4)°, V = 1047.194(8) Å3) and high resolution powder XRD data. The formed interstitial hydride disproportionates during heating forming NdH2. Nd2Ni2Mg is an antiferromagnet with the Néel temperature TN ≈ 19 K. Presence of another magnetic phase transition at 14 K together with two metamagnetic transitions indicates a complicated magnetic phase diagram. The hydrogenation reduces TN to 1.0 K.