| AVS 63rd International Symposium & Exhibition | |
| Actinides and Rare Earths Focus Topic | Wednesday Sessions |
| Session AC+MI-WeM |
| Session: | Magnetism, Complexity, and Superconductivity in the Actinides and Rare Earths (8:00-11:00 am)/Actinide and Rare Earth Theory (11:00 am-12:20 pm) |
| Presenter: | Silvie Maskova, Charles University in Prague, Czech Republic |
| Authors: | S. Maskova, Charles University in Prague, Czech Republic K. Miliyanchuk, Ivan Franko National University of Lviv, Ukraine S. Danis, Charles University in Prague, Czech Republic B. Vondrackova, Charles University in Prague, Czech Republic O. Stelmakhovych, Ivan Franko National University of Lviv, Ukraine L. Havela, Charles University in Prague, Czech Republic |
| Correspondent: | Click to Email |
U-based ternary compounds, which were studied in large isostructural series, allow large variations of the 5f localization due to variable 5f-5f overlap and the 5f hybridization with the d- and p-states. An additional tuning parameter is the H absorption, working primarily as a negative pressure. At 5f-band systems it leads to enhancement of magnetic properties in most of cases [1]. However, this tool is restricted to cases in which substantial H absorption can be achieved. In the system of UTX compounds (T = later transition metal, X = p-metal) with the ZrNiAl structure type, a high absorption was registered only for UNiAl, leading to UNiAlH2.3, in which the Neel temperature is enhanced from 19 K to 95 K. Recently we discovered a new UTX compound, UNiZn [2], which is itself non-magnetic, as the 5f-p hybridization is stronger in the case of smaller Zn than for larger Al. This material forms an equivalent hydride, UNiZnH2.3, which is antiferromagnetic (below 50 K). This opened a possibility to study systematically the onset of antiferromagnetism in the system UNiZn-UNiAl and variations of properties of related hydrides. We found that the magnetic order in the precursors sets in between 10 and 30 at.% Al. The Sommerfeld coefficient of electronic specific heat γ increases from 94 mJ/mol.K2 in UNiZn and reaches 360 mJ/mol.K2 in the critical area and then it decreases for a higher Al concentration to 164 mJ/mol.K2 in UNiAl, which is known as a mid-weight heavy fermion. [3]. The hydrides exhibit lower γ-values. γ = 100 mJ/mol.K2 in the UNiZn hydride decreases monotonously to 67 mJ/mol.K2 in the hydride of UNiAl. The situation implies that reducing the 5f-p hybridization even more, we may proceed with strengthening of magnetism in the sense of further increasing TN and decreasing γ. The natural counterpart of UNiAl is UNiGa with the same structure type but larger X-ligand. However, no attempt to synthesize a hydride of UNiGa was successful in the past. In the present work we undertook a study of the hydrides of quasi-ternary system UNiAl-UNiGa [4], and found that the H absorption can be reached even for high Ga concentrations. Physical properties of Ga-substituted hydrides are currently explored.
[1] S. Maskova, L. Havela, E. Santava, and K. Miliyanchuk, J. of Physics: Conf. Ser.200 (2010) 032040.
[2] S. Maskova, S. Danis, K. Miliyanchuk, O. Stelmakhovych, B. Vondrackova, A.V. Kolomiets, L. Havela, J. Alloys Comp. 646 (2015) 885-892.
[3] L. Havela, K. Miliyanchuk, A. Kolomiyets: Int.J.Mat.Res. 100 (2009) 1182-1186.
[4] H. Maletta, V. Sechovsky, P.A. Veenhuizen, F.R. de Boer, L. Havela, and G. Hilscher, Z.Phys. B – Cond. Matter 72 (1988) 455-460.