Experimental Study of the Host NMR Linewidth and Spin-Lattice Relaxation Rate in DiluteCuFeAlloys below the Kondo Temperature

Abstract

In order to determine the properties of single magnetic impurities in the Kondo state and the effects of these single magnetic impurities on the host-conduction-electron spin system, the Fe-impurity contributions to the ${\mathrm{Cu}}^{63}$-host nuclear-magnetic-resonance (NMR) linewidth $\Delta H_i$, and spin-lattice relaxation time $T_{\mathrm{li}}$, have been studied over a wide Fe-concentration range ($0<c<\mathrm{}1260\mathrm{}$ ppm) in $\mathrm{Cu}\mathrm{Fe}$. The NMR-linewidth measurements made from 1.65 to 77°K and in magnetic fields from 2 to 16 kOe and in some cases up to 60 kOe, show the anomalous behavior of the slope $S=\frac{d\Delta H_i}{\mathrm{dH}}$ originally observed by Heeger et al. and studied for a 480-ppm $\mathrm{Cu}\mathrm{Fe}$ alloy by Golibersuch and Heeger exists over a wide Fe-concentration range. This anomalous behavior, which consists of the transition from a constant slope at low fields, $S_L$, to a smaller magnitude slope at high fields, $S_H$, occurs in a relatively narrow range of fields about some critical field $H_c$. This behavior clearly results from the single-impurity contribution to the NMR linewidth as evidenced by the linear concentration dependence of both $S_L$ and $S_H$ and also by the concentration independence of $\frac{S_L}{S_H}$. $S_H$ has the same ${\mathrm{}(T+29\mathrm{})\mathrm{}}^{-1\mathrm{}}$ temperature dependence as the bulk susceptibility, while $S_L$ is enhanced for $H<\mathrm{}{H}_c$ and $T<\mathrm{}{T}_c\approx 6$ °K. At 1. 65 °K, $S_H=(1.50\mathrm{}\pm 0.10)\times {10}^{-6\mathrm{}}c$, $S_L=(2.83\mathrm{}\pm 0.10)\times {10}^{-6\mathrm{}}c$ ($c$ in ppm), and $\frac{S_L}{S_H}=1.9\mathrm{}$. These results show that the Ruderman-Kittel-Kasuya-Yosida-like oscillatory conduction-electron spin polarization existing about an impurity for $T\gg T_K$ is either enhanced for $T<\mathrm{}{T}_c$ and

Keywords

• SPIN POLARIZATION
• RELAXATION TIME
• NUCLEAR MAGNETIC RESONANCE
• CRITICAL FIELD
• DIPOLAR COUPLING
• MAGNETIC FIELD

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