Hyperfine fields at the anion sites in ${\text{USb}}_{1-x}{\text{Te}}_x$ and $f\text{−}p$ hybridization

We report a low-temperature (4.2 K) ${}^{121}\text{S}\text{b}$ and ${}^{125}\text{T}\text{e}$ Mössbauer study of the ${\text{USb}}_{1-x}{\text{Te}}_x$ solid solutions. Large transferred hyperfine fields are observed at the ligand sites in the magnetically ordered state of the compounds. The hyperfine field is found to be positive and isotropic in the ferromagnetic samples. The large anisotropic contribution to the hyperfine field observed in the antiferromagnetic type I and type IA phases is interpreted as resulting from the spin polarization of the ligand $5p$ states induced via strong hybridization with the uranium $5f$ valence band.

Figure 1

Magnetic phase diagram of the ${\text{USb}}_{1-x}{\text{Te}}_x$ solid solutions as a function of temperature and tellurium concentration [adapted from Rossat-Mignod et al. (Ref. 2)]

Figure 2

Low temperature magnetic structures observed in the ${\text{USb}}_{1-x}{\text{Te}}_x$ solid solutions. Antiferromagnetic (AFM) triple-$k$ type I ordering $\left(x<0.09\right)$, AFM triple-$k$ type IA ordering $\left(0.12<x<0.17\right)$, ferromagnetic (FM) ordering $\left(x>0.18\right)$. The uranium magnetic moments point along $⟨111⟩$ directions in all magnetic structure types. The Sb or Te anions (large circles) have an octahedral environment of six nearest U—neighbors [adapted from Rossat-Mignod et al. (Ref. 2)].

Figure 3

${}^{121}\text{S}\text{b}$ (top) and ${}^{125}\text{T}\text{e}$ (bottom) Mössbauer spectra of ${\text{USb}}_{0.5}{\text{Te}}_{0.5}$ taken at 4.2 K. The solid lines are the best fits to the data points assuming pure magnetic interactions.

Figure 4

Transferred hyperfine fields (4.2 K) at the anion nuclei (${}^{121}\text{S}\text{b}$ and ${}^{125}\text{T}\text{e}$) in the ${\text{USb}}_{1-x}{\text{Te}}_x$ solid solutions as a function of the tellurium concentration $\left(x\right)$. The crosses are an estimate of the hyperfine fields in the hypothetical ferromagnetic state of USb and ${\text{USb}}_{0.85}{\text{Te}}_{0.15}$. Their values are obtained from a linear extrapolation of the fields observed in the ferromagnetic phases $\left(x\ge 0.2\right)$

Figure 5

${}^{125}\text{T}\text{e}$ Mössbauer spectra of UTe taken at 4.2 K in zero applied field (top) and in a longitudinal applied field of 50 kOe (bottom). The solid lines are the best fits to the data points (see text).