Experimental study of the competition between Kondo and RKKY interactions for Mn spins in a model alloy system

The quasicrystal Al-Pd-Mn is a model system for an experimental study of the competition between Ruderman-Kittel-Kasuya-Yoshida (RKKY) and Kondo interactions. First, specific of such alloys, only a few Mn atoms carry an effective spin and their concentration $x$ is tunable over several orders of magnitude, even though the Mn amount is almost constant. Second, the characteristic energy scales for the interactions lie in the Kelvin range. Hence we could study the magnetization on both side of these energy scales, covering a range of temperatures $(0.1\char21{}100\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ and magnetic fields (${\ensuremath{\mu}}_{B}H∕{k}_{B}=0\char21{}5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$) for 22 samples and $x$ varying over two decades. Using very general Kondo physics arguments, and thus carrying out the data analysis with no preconceived model, we found a very robust and simple result: The magnetization is a sum of pure Kondo $({T}_{K}=3.35\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ and pure RKKY contributions, whatever the moment concentration is and this surprisingly up to the concentration where the RKKY couplings dominate fully and thus cannot be considered as a perturbation.