Nuclear Magnetic Resonance ofFe57in the Paramagnetic AlloysTiFe1−xCox

Abstract

Nuclear magnetic resonances (NMR) of ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ in isotopically enriched specimens of TiFe, Ti${\mathrm{Fe}}_{0.8}$ ${\mathrm{Co}}_{0.2}$, and Fe${\mathrm{Cl}}_3$, and of Ti in TiCo are reported. The results supplement existing Fe Mössbauer and Co NMR information on the pseudobinary $\mathrm{Ti}{\mathrm{Fe}}_{1-x}{\mathrm{Co}}_x$. The Knight shift (and estimated uncertainty) of iron in TiFe is + (1.29±0.03)% at room temperature and + (1.34±0.03)% at 77K, yielding a hyperfine coupling constant of + (3±2) kG/μB per formula unit. Similar values are obtained for iron in Ti${\mathrm{Fe}}_{0.8}$ ${\mathrm{Co}}_{0.2}$. The Knight shift of Ti in TiCo is + (0.07±0.02)% at room temperature, and - (0.06±0.03)% at 77K, yielding a hyperfine coupling constant of - (12±3) kG/μB per formula unit for Ti in TiCo, contrasting with a near-zero coupling constant for Ti in TiFe. Both the orbital shifts and the $d$-spin hyperfine coupling constants for the Fe and Ti sites are much less dependent on cobalt concentration than these same quantities at the cobalt site. The NMR results on the three constituents of $\mathrm{Ti}{\mathrm{Fe}}_{1-x}{\mathrm{Co}}_x$ suggest: (i) $s-d$ admixture in the wave-function character at the Fermi surface for the (Fe,Co) sublattice, (ii) greater $s$ admixture and perhaps a greater $d$-spin moment at an iron site than at a cobalt site in the iron-rich compounds, and (iii) a nuclear moment for cobalt corresponding to a nuclear gryomagnetic ratio $\gamma =2\mathrm{}\pi \times 1.003$ kHz/G. The Knight shift of dilute Fe in Ti as measured by the Mössbauer effect is (0±1)%. The chemical shift of Fe in enriched aqueous Fe${\mathrm{Cl}}_3$ is found by NMR to be + (0.40±0.04)%.