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|Title:||Hydrides of TbM2 (M = Fe and Mn)|
|Authors:||Kulshreshtha, S K|
Jayakumar, O D
|Abstract:||Intermetallics TbFe2, TbFeMn and TbMn2 having C-15 cubic Laves phase structure, have been prepared and hydride to varying values of H/M using gas phase method up to a saturation composition of H/M ≈ 1.6. TbFe2H, samples show the formation of a metastable rhombohedral phase for higher values of x, which on equilibration with hydrogen transforms to cubic form. Unlike this, TbFeMn shows the existence of both hydrided and unhydrided phases for x ≤ 3.0 and for higher values of x, uniform hydriding takes place and a saturation composition of TbFeMnH4.8 which is characterized by cubic structure with 'a' = 8.137Å, is obtained. For TbMn2Hx, for x ≥ 1.2, the formation of a tetragonal phase is observed. Mossbauer study of TbFe2Hx samples reveals that for TbFe2, the Fe spins are aligned along (111) direction, which on hydriding become non-collinear and shift towards (100) direction for TbFe2H3.15 composition. Mossbauer spectra of TbFeMn are complex and suggest a non-collinear spin alignment due to the existence of both ferromagnetic and anti ferromagnetic interactions between transition metal elements and show a systematic decrease in magnetic field and magnetic transition temperature due to hydrogen incorporation in the matrix. Temperature programmed hydrogen desorption studies of TbFe2Hx and TbFeMnHx samples exhibit broad peaks in the region 225-350°C, due to overlap effects and peak maxima shift slightly towards higher temperature side with Mn substitution. Unlike this, TbMn2Hx samples exhibit much better resolved TPR curves consisting of mainly three peaks placed over the region 275-400°C, possibly because of the tetragonal structure of these samples.|
|Appears in Collections:||IJC-A Vol.42A(07) [July 2003]|
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