TbMgNi(4–x)Co(x)–(H,D)(2) System. II: Correlation between Structural and Magnetic Properties

[Image: see text] The magnetic properties of TbMgNi(4–x)Co(x) intermetallic compounds and selected hydrides and deuterides of this system have been studied by various techniques, including magnetic measurements, in situ X-ray and neutron powder diffraction. The intermetallic compounds crystallize in a SnMgCu(4)-type structure and magnetically order below a Curie temperature (T(C)), which increases exponentially with the Co content. This can be due to the ordering of the Co sublattice. On the other hand, the insertion of D or H in TbMgNiCo(3) strongly decreases T(C). The X-ray diffraction measurements versus temperature reveal cell volume minima at T(C) for the compounds with x = 1–3 without any hints of the structure change. The analysis of the neutron diffraction patterns for the intermetallics with x = 2 and 3 indicates a slightly canted ferrimagnetic structure below T(C). The Tb moments refined at 16 K are 4.1(2) μ(B)/Tb for x = 2, and 6.2(1) μ(B)/Tb for x = 3, which are smaller than the free ion value (9.5 μ(B)/Tb). This reduction can be due to the influence of temperature but also reveals the crystal field effect. As Ni and Co occupy statistically the same Wyckoff site, an average Ni/Co moment was refined, leading to 1.7(2) μ(B)/atom for x = 2 and 1.8(1) μ(B)/atom for x = 3 at 16 K. This moment is slightly canted compared to the Tb moment.