| AVS 62nd International Symposium & Exhibition | |
| Actinides and Rare Earths Focus Topic | Wednesday Sessions |
| Session AC+AS+MI-WeM |
| Session: | Magnetism, Complexity and Superconductivity in the Actinides and Rare Earths |
| Presenter: | Silvie Maskova, Charles University, Prague, Czech Republic |
| Authors: | S. Maskova, Charles University, Prague, Czech Republic R.V. Denys, Institute for Energy Technology, Kjeller, Norway I. Halevy, Nuclear Research Center Negev, Beer-Sheva, Israel K. Miliyanchuk, Ivan Franko National University of Lviv, Lviv, Ukraine L. Akselrud, Ivan Franko National University of Lviv, Lviv, Ukraine A. Kolomiets, Lviv Polytechnic National University, Lviv, Ukraine V. Yartys, Institute for Energy Technology, Kjeller, Norway M. Giovannini, University of Genova, Genova, Italy L. Havela, Charles University, Czech Republic |
| Correspondent: | Click to Email |
We have been studying some members of large family of A2T2X (A = Rare-Earth (RE) or actinide, T = transition metal, X = p-metal) compounds crystallizing in the Mo2FeB2 structure type (space group P4/mbm). U2T2X interact with H2 only at high pressure (≈ 100 bar) reaching 2 H/f.u. The H absorption produces a lattice expansion, while the tetragonal structure is preserved. The H atoms presumably enter the 8k position inside the U3T tetrahedra occupied randomly up to 50%. On the other hand, it was found that some RE2T2X compounds can absorb more hydrogen compared to their U-counterparts in much lower H pressures. The amorphization of the structure upon hydrogenation (4 H/f.u.) was found for RE2Pd2In(Sn) with light RE (La, Nd). RE2Pd2In(Sn) with heavy RE behave similar way as U2T2X compounds (2 H/f.u., crystal structure type not changed). For the isostructural indide Nd2Ni2In the hydrogen absorption of 7 H/f.u. leads to the orthorhombic distortion of the crystal structure.
Recently, we have been studying several isostructural RE2T2Mg (T = Ni, Pd). The H absorption in these compounds depends on the type of transition metal. The compounds with Ni tend to absorb up to 8 H/f.u. The crystal structure is changed to monoclinic (space group P21/c). If the transition metal is Pd, the hydrogen absorption is lower, reaching approx. 6 H/f.u. and the crystal structure is modified in different way. The Tb2Pd2Mg-hydride crystallizes in a new ternary structure type (Fmmm). In the case of Mg-compounds, the hydrogen absorption in not reversible. Upon desorption of H the initial crystal structure is not restored.
We have found that in U-compounds the ordering temperatures increase upon hydrogenation contrary to the RE-compounds where the ordering temperatures are dramatically reduced. Magnetic properties of U-compounds strongly depend on the inter-U distances. Hydrogen intrusion modifies the lattice by expanding it without changing the crystal-structure type leading to a band narrowing. As a consequence doping of U intermetallics by interstitial hydrogen leads to stronger magnetic properties. On the other hand, the hydrogen absorption has opposite effect on magnetic properties of RE2T2X compounds. For RE compounds, hydrogenation affects mainly the 4f – magnetic moments and their ordering. The exchange coupling is reduced presumably by reducing the concentration of conduction electrons.