Nuclear Magnetic Resonance in UAl2

Abstract

The nuclear magnetic resonance of ${\mathrm{Al}}^{27}$ in U${\mathrm{Al}}_2$ has been observed in the range of temperatures 4-300°K. Large Knight shifts ($K$) were found with a temperature dependence not of a Curie-Weiss type. This behavior and the temperature independence of the linewidth, when considered in conjunction with susceptibility ($\chi$) measurements, indicate (1) no localization of the magnetization of the U ($5f$ and/or $6d$) electrons and (2) no magnetic ordering exists. These results are contrasted with those obtained on the isostructural $X{\mathrm{Al}}_2$ ($X=\mathrm{r}\mathrm{a}\mathrm{r}\mathrm{e}-\mathrm{e}\mathrm{a}\mathrm{r}\mathrm{t}\mathrm{h}\mathrm{i}\mathrm{o}\mathrm{n}$) metals. Using a simple model, certain features of the band structure and the effective exchange interaction between itinerant $f$ and $s$ electrons may be deduced. From the extrapolated limit of the linear $K$ vs $\chi$ curve a large positive temperature-independent contribution to $\chi$ is obtained which is attributable to the Kubo-Obata orbital paramagnetism to be expected in metals with unfilled degenerate bands.