Nuclear magnetic resonance in single crystals of dilute magnetic alloys

Abstract

We have observed nuclear resonances from $^{63}\mathrm{Cu}$ nuclei in the first few shells around Fe, Co, and Ni impurities present in low concentrations of single crystals of copper. The resonances appear as weak satellites displaced in field $\ensuremath{\delta}H$ form the much stronger resonance from $^{63}\mathrm{Cu}$ nuclei far from the impurities. Study of the dependence of the various $\ensuremath{\delta}H'\mathrm{s}$ on the orientation of the static field ${\stackrel{\ensuremath{\rightarrow}}{H}}_{0}$, with respect to the crystal axes enables one to determine which satellites go with which shell of neighbors, and to deduce the quadrupolar, dipolar, and pseudodipolar coupling parameters for the observed shells. By these means we have been able to assign shells to satellites seen in powder samples. For $\mathrm{Cu}\mathrm{Fe}$ we identify the second and third shells, for $\mathrm{Cu}\mathrm{Co}$ the first and second, and for $\mathrm{Cu}\mathrm{Ni}$ the first. The observation that the pseudodipolar coupling of the first shell in $\mathrm{Cu}\mathrm{Co}$ is strongly nonaxial proves that there are strong crystal-field effects. For the first neighbor to the Co the pseudodipolar coupling is about twice the direct dipolar coupling. For $\mathrm{Cu}\mathrm{Fe}$ the same is true for the third neighbor shell.