Magnetic hyperfine fields at¹¹⁹Sn probe nuclei on the R sites of the cubic rare-earth Laves-phase compounds RFe₂and RCo₂

Abstract

The magnetic hyperfine interaction of the 119 Sn probe nucleus on the R site of the ferro-and ferrimagnetic RFe 2 (R = Sm-Tm, Lu, Zr, Hf and U) and RCo 2 (R = Gd-Er) compounds has been investigated by Mössbauer spectroscopy technique. It was found that the magnetic hyperfine fields (B hf ) exhibit quite different behaviours in the two series of the compounds. For the RFe 2 compounds, the ratio B hf /µ 3d remains essentially constant across the series at a value of 30 T/µ B (within ±4%), also for nonmagnetic R = Zr, Lu and Hf. This means that a contribution to B hf from the 4f magnetic moments of the R sublattice is absent. In RCo 2 compounds, the total hyperfine field is the sum of two contributions: one is the 4f contribution (B 4f ) and the other is 3d contribution (B 3d ). The 3d and 4f contributions have the same relative sign; both contributions are positive with respect to the 3d moments direction. The B 4f contribution is relatively large: the ratio B 4f /B 3d varies from about 0.4 (ErCo 2 ) to about 0.7 (GdCo 2 ). The results demonstrate that the transfer of the electron polarization from the R atoms to the hybrid bonds is extremely sensitive to the features of the 3d electrons of the transition-metal subsystem.

Local magnetic moment formation at 119Sn Mössbauer impurity in () Laves phases compounds

“…In the case of RFe 2 intermetallics, we adopted J sd ¼ 0:6 Â 10 À3 in units of the s-p bandwidth of RFe 2 hosts and /S Fe S were obtained from Ref. [7]. Keeping fixed these parameters, we self-consistently determined the local magnetic moment and the corresponding magnetic hyperfine field at the Sn impurity.…”

“…We start the description of a Sn impurity diluted in RFe 2 intermetallic hosts by considering that the local magnetic moments and the total magnetic hyperfine fields have two important contributions, namely, (i) the contribution from R ions and (ii) the contribution from the coupling with the induced magnetic moments at the Fe sites [7]. In order to account for both contributions to the formation of the local magnetic moments, we consider the RFe 2 intermetallic compounds as being an effective ferromagnetic rare-earth hosts [22], with an extra term to account for the polarization arising from the magnetic moments of the transition elements surrounding the impurity site [22].…”

“…Moreover, in the recent years the systematics of the hyperfine fields at s-p impurities have been experimentally studied in RM 2 Laves phases intermetallic compounds (R ¼ rare À earth metals; M ¼ Fe; Co; Ni) [4][5][6][7].…”

Mapping the magnetic hyperfine field in GdCo5

“…As the 1a and 2c sites have axial symmetry, the main components V z z of the electric field gradient for both sites are also directed along the c axis. Since Gd and Co magnetic moments are aligned with the c 8 despite the fact that Y atom in YCo 5 has 18 Co atoms as the nearest neighbors (nn) and the Lu atom in LuFe 2 has only 12 nn Fe atoms. This fact may indicate that the 6 Co I atoms (lying in the basal plane) do not give a significant contribution to B 1a field because it is formed by the Co I I magnetic moments arranged in hexagonal 3g layers and directed along the c axis.…”

“…8 At the same time, the Gd sites have only four Gd nn in GdFe 2 , twice less than in GdCo 5 . It follows from this that the contributions from Gd sublattice to the HFs for 119 Sn probes in GdCo 5 and GdFe 2 compounds are proportional to the number of the Gd magnetic moments in the nearest environment of tin probe atoms.…”