Sn Hyperfine Fields Research Articles

1 1 9Sn Mössbauer study of the evolution of the magnetic state in U(Sn,Pb)3

USn3 is a highly enhanced paramagnet that is very near a magnetic instability, and UPb3 has an antiferromagnetic transition at 31.3 K. As Sn is substituted for Pb in U(Sn1−xPbx)3, the Néel temperature, TN, initially increases to 38 K at x=0.7, then decreases, and appears to go to zero for x≲0.1. The temperature dependence of the magnetic susceptibility for 0≤x≤1.0 and 119Sn Mössbauer spectra for 0≤x≤0.98 have been measured. The Mössbauer spectra indicate that the antiferromagnetic structure for the Pb-rich pseudobinary alloys is not type I as previously reported. As x decreases, at least two, and possibly four, distinct Sn hyperfine field sites are found. The saturation hyperfine fields at the Sn sites do not show as pronounced a variation with concentration as is seen in TN. For larger x the saturation hyperfine fields are independent of x, which suggests that the U magnetic moments are nearly constant for the Pb-rich pseudobinary alloys, and then drop rapidly to zero at the magnetic instability. The fraction of Sn sites seeing a particular hyperfine field is observed to vary monotonically across the series.

Sn hyperfine field systematics in Rh2MnZ Heusler alloys

Sn hyperfine fields were measured using Mössbauer spectroscopy in the Heusler alloys Rh2MnZ (Z = Ge, Sn). The measurements yielded values of −48 and +31 kOe at 77 K for Sn in Rh2MnGe and Rh2MnSn, respectively. These values showed that in these alloys the Sn hyperfine field decreases with increasing conduction electron density. These results are compared with those obtained for Sn hyperfine fields in X2MnZ and Co2YZ Heusler alloys and are discussed in terms of theoretical predictions.

Crystallization and magnetic properties of amorphous Fe-Sn-B-Si alloys

Amorphous alloys of the form Fe79SnB20−xSix (x=0,2,5,9,12) were prepared by quenching from the melt. The crystallization was characterized by differential thermal analysis (DTA) measurements. Alloys with x=0 and x=2 show single DTA peaks at 450°and 475 °C, respectively. Alloys with x≥5 show two DTA peaks corresponding to the crystallization of Fe–Si phases at a lower temperature and Fe–B phases at a higher temperature. Magnetization measurements yield magnetic moments on the Fe ions which increase from 1.87μB in Fe79SnB20 to 1.97μB in Fe79SnB8Si12. Mössbauer effect measurements give values of the Fe and Sn hyperfine fields of approximately 285 k and +29 kOe, respectively, which are essentially independent of x. The width of the field distribution for both sites is found to remain nearly constant across the series as well.

Sn hyperfine field trends in the Heusler alloys Co2Mn(Al, Si)

The Sn hyperfine field in the series of Heusler alloys Co2MnAl0.98−xSixSn0.02 (x=0.00, 0.20, 0.40, 0.58, 0.78, 0.98) has been measured at 77 K using119Sn Mossbauer effect. The measurements show an approximately linear decrease in field across the series from a value of +40 kOe in Co2MnAl0.98Sn0.98 to a value of −16 kOe in Co2MnSi0.9xSn0.9x. These results are discussed in terms of previous results for Sn hyperfine fields in Co-based Heusler alloys and theoretical predictions for non-magnetic site hyperfine fields in ferromagnetic hosts.

Conduction electron contributions to the Sn hyperfine field in the Heusler alloy Co2Ti1−xVxSn

Vibrating sample magnetization and 119Sn Mössbauer effect measurements were made on the series of Heusler alloys Co2Ti1−xVxSn (x=0.0, 0.2, 0.4, 0.6, 0.8, 1.0) to determine the moment carried by the Co atoms μ and the Sn hyperfine field H. These measurements yielded values of the field of +80 and +7 kOe and moments of 0.88 and 0.31 μB for the alloys Co2TiSn and Co2VSn, respectively. The Sn field showed a monotonic decrease as a function of x. The moment remained relatively constant for x≤0.8 and decreased dramatically for x=1.0. The results obtained here are discussed in terms of recent theoretical predications.

Sn magnetic hyperfine field crossover in the Heusler alloys (Ni1−xPdx)2MnSn

119Sn Mössbauer effect and bulk magnetization measurements were performed on the series of Heusler alloys (Ni1−xPdx)2MnSn (x=0.0, 0.15, 0.30, 0.40, 0.60, 0.70, 0.85, and 1.0) at 4.2 K. The Sn hyperfine field showed a linear decrease from +94 kOe in Ni2MnSn to −39 kOe in Pd2MnSn. The magnetization measurements gave values of 81 emu/gm in Ni2MnSn and 51 emu/gm in Pd2MnSn and yielded moments of approximately 4 μB per Mn atom in all the alloys in the series. The change in Sn hyperfine field may be explained most simply in terms of a changing conduction electron density which results from changes in the lattice parameter. Theoretical predictions of Jena and Geldart, as well as Blandin and Campbell, are discussed.

HYPERFINE FIELDS IN Co-BASED HEUSLER ALLOYS

From Mossbauer experiments with 19Sn, 121Sb and 178Hf we have determined the hyperfine fields at Sn, Sb and Hf, respectively, in Heusler alloys of the composition CozVSn, CozNbSn, CozHfSn, Co2-,FezTiSn (x = 0.2, 0.4), C O ~ ~ N ~ ~ T ~ S ~ (x = 0.1, 0.2) and Co2TiSn0.9Sbo.l. Moreover, the hyperfine field at Ta on the Hf site in CozHfSn alloy has been measured by the time differential perturbed angular correlation method. The results are discussed in terms of the electronic structure of these alloys. In particular, the observed anomalies in the tin hyperfine field are explained by the assumption that the polarization of the p-electrons of tin depends decisively on the nature of the neighbouring nonmagnetic transition metal atoms. Introduction. In the ferromagnetic Heusler alloys Co2YSn, where the magnetic Y atoms are either the group IVa elements Ti, Zr and Hf or the group Va elements V and Nb, both the Co and Sn hyperfine fields have rather anomalous values. Thus the NMR value for the Co hyperfine field in Co2TiSn is + 21 kOe [I], while a negative sign would be expected if the core polarization hypedine field were the dominant contribution, as it usually is. Mossbauer experiments, on the other hand, yield [l] large positive hyperline fields of+ 82, + 88 and + 106 kOe at Sn in Co,TiSn, Co,ZrSn and Co2HfSn, respectively. These positive values of the Sn fieIds are suprising because the only magnetic atoms in these systems are the Co atoms, the contribution of which to the Sn hyperfine field should be negative according to the