Magnetic hyperfine fields in Y2Fe17?x Si x compounds

Theoretical study of structure, magnetism and lattice vibrations of intermetallics Lu2(Fe, T)17 and their hydrides

“…So, in the calculation, T atoms preferentially occupy the 4f sites and avoid the 6g sites. This is in agreement with experimental findings [19,20]. The order of the site preference is 4f, 12k, 12j and 6g for Lu 2 Fe 17Àx T x .…”

X-ray diffraction, magnetization and nuclear magnetic resonance study of

“…They attribute the increase in T c to the preferential substitution. The NMR results reported by Ge et al [23] however, appear to be inconsistent with the Mössbauer results of Morariu et al [22] cited above. On the other hand, for Ga substitution into the Nb 2 Fe 17 and Tb 2 Fe 17 parent systems, Hu et al [25] have carried out both Mössbauer effect and neutron diffraction studies on rhombohedral Nb 2 Fe 17−x Ga x and Tb 2 Fe 17−x Ga x , and find that Ga completely avoids the 9d sites, occupies the 6c dumbbell sites only for x 5, and strongly prefers the 18f sites for large x. Consequently, they conclude that the initial T c enhancement in these systems is not a result of the replacement of Fe(6c) atoms by Ga. From the work to date on the substitutional systems, a picture of the T c enhancement is emerging; however, a complete understanding is still lacking.…”

“…Generally speaking, substitutional systems also exhibit lattice expansion ( 9%) along with the T c enhancement; however, there are notable exceptions. For example, the substitution of Si for Fe in Y 2 Fe 17 Si x increases T c even though the lattice contracts [23]. An alternative explanation for the enhancement of T c in the substitutional systems is based on the preferential substitution of Si, Al and Ga for Fe at the dumbbell sites which leads to a disappearance of Fe-Fe antiferromagnetic interactions at these sites [24].…”

“…Concerning the issues of preferential site selection and T c enhancement, two previous reports are particularly relevant to the results presented here. For the Y 2 Fe 17 parent system and Si substitution, Ge et al [23] have carried out a 89 Y NMR study on hexagonal Y 2 Fe 17−x Si x and report that the Si atoms do preferentially enter the dumbbell 4f sites for x 1.0. This conclusion is based on the separation of the 2b and 2d 89 Y peaks, and the fact that Y(2b) has two dumbbell Fe atoms as nearest neighbours while Y(2d) has none.…”

Atomistic study of structural simulation and Curie temperature of R2Fe17–xTx (R = Tb, Ho, Er; T = Ti, V, Cr, Mn)

“…In the range 0 < x < 2, the cohesive energy of R 2 Fe 17-x Cr x decrease most significantly when the 4f sites are occupied by Cr; for the 12j and12k sites, the energy decreases less, and for the 6g sites, the cohesive energy is comparatively high. So Cr atoms will preferentially and simultaneously occupy the 4f sites, which correspond with some experiments [26,27]. When the composition range x > 2, Cr atoms should first occupy all of the 4f sites of the hexagonal Th 2 Ni 17 -type structure based on the above analysis, and then with the 4f sites full Cr atoms should enter into part of the 6g, 12j or 12k sites.…”