Quantized Hyperfine Field at an Implanted ${\mu }^{+}$ Site in ${\mathrm{PrPb}}_3$: Interplay between Localized $f$ Electrons and an Interstitial Charged Particle

The local effect of an interstitial hydrogenlike particle on localized $f$ electrons was studied in ${\mathrm{PrPb}}_3$ by means of ${\mu }^{+}$ spin rotation and relaxation. Spontaneous ${\mu }^{+}$ spin precession with harmonic frequencies was observed for the first time in $f$ electron compounds. We demonstrate that the signal is derived from a coupling between the ${\mu }^{+}$ spin and the hyperfine-enhanced nuclear spin of nearest neighbor (NN) ${}^{141}\mathrm{Pr}$ with Ising-like anisotropy. The signal also suggests a marked suppression of spin dynamics of the NN ${}^{141}\mathrm{Pr}$ in comparison with that of the bulk ${}^{141}\mathrm{Pr}$. These facts strongly indicate modification of the $f$ electronic state due to the interstitial charged particle.

Figure 1

The temperature dependence of the ${\mu }^{+}$ Knight shift in a magnetic field ${\mu }_{0}H=2\mathrm{T}$ applied along the [001] direction. The inset shows the ${\mu }^{+}$ localization site.

Figure 2

(a) $\mathrm{ZF}\mathrm{\text{−}}{\mu }^{+}\mathrm{SR}$ spectra. The base lines are shifted by 0.1 as the temperature increases. The solid curves are the best fits with Eq. (7). (b) FFT spectra of the $\mathrm{ZF}\mathrm{\text{−}}{\mu }^{+}\mathrm{SR}$ signals.

Figure 3

The spontaneous ${\mu }^{+}$ spin precession frequencies as functions of temperature. The inset is the $f_i$ versus $f_1$ plot ($i>1$). The solid lines represent the linear fits.

Figure 4

The fundamental frequency ${\omega }_f/2\pi$ ($=f_1$) versus the $K_{\parallel }$ in a field of 2 T. The solid line indicates a linear fit.