The ground state of metallic nano-structures in heavily irradiated NaCl-KBF4

Abstract

ESR, NMR and static magnetic susceptibility measurements of heavily irradiated NaCl-K and NaCl-KBF 4 are reported. Up to 10% of the NaCI-molecules are transformed into metallic Na nanoparticles and Cl 2 precipitates. In addition, there are paramagnetic F- and F-aggregates, which are coupled by exchange interactions to the conduction electrons in the nanoparticles. Above 160K the NMR and ESR signals of NaCl-K and NaCl-KBF 4 show Pauli paramagnetism and the properties of the Na nanoparticles are similar to bulk sodium. A single ESR line is observed revealing exchange interaction between conduction electrons in the nano-particles and F-aggregates. The observed decrease of the ESR susceptibility with decreasing temperature is due to a metal-insulator transition. The conduction electrons are localized below 40 K and the above mentioned F-aggregate centers contribute significantly to the overall ESR signal. For NaCl-KBF 4 we observed that with decreasing temperature the ESR line shifts towards lower fields due to antiferromagnetic ordering and internal magnetic fields.