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TbMgNi4-Co-(H,D)2 System. II: Correlation between Structural and Magnetic Properties
Valérie Paul-Boncour1, Premysl Beran2,3, Charles Hervoches2
1Université Paris-Est Créteil, CNRS, ICMPE, UMR 7182, F-94320 Thiais, France.
Abstract:
The magnetic properties of TbMgNi4-Co 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 SnMgCu4-type structure and magnetically order below a Curie temperature (TC), 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 TbMgNiCo3 strongly decreases TC. The X-ray diffraction measurements versus temperature reveal cell volume minima at TC 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 TC. The Tb moments refined at 16 K are 4.1(2) μB/Tb for x = 2, and 6.2(1) μB/Tb for x = 3, which are smaller than the free ion value (9.5 μB/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) μB/atom for x = 2 and 1.8(1) μB/atom for x = 3 at 16 K. This moment is slightly canted compared to the Tb moment.
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