Nuclear interactions in metallic Van Vleck paramagnets: NMR in single-crystal PrNi_{5}

Abstract

NMR measurements on single-crystal Pr${\mathrm{Ni}}_5$ in the range $1.2<~T<~8$ K are presented. The magnetic-field enhancement factors (${\alpha }_{\parallel }=6.56\mathrm{}$ and $a_{\perp }=13.13\mathrm{}$ at 1.2 K) and the quadrupole parameter ($P<~0.6$ MHz) are determined microscopically from the angular dependence of the resonance field and the linewidth, respectively. The susceptibility of the Pr ions alone is shown to be smaller than the total value of $\chi$ [$\chi \left(\mathrm{ions}\right)\simeq {0.8}_{\chi } \left(\mathrm{bulk}\right)$]. The enhanced value of $\chi$ (ions), as well as the temperature dependence of the linewidth, are interpreted in terms of Pr-Pr exchange-induced mechanisms with $\lambda \simeq 3.5$ mole/emu. Nuclear ordering temperatures are estimated, with $T_c\mathrm{}\left(P\right)\mathrm{}\lesssim 0.05$ mK and $T_c\left(\lambda \right)\lesssim 0.4$ mK.