Electron spin resonance and nuclear magnetic resonance of sodium macrostructures in strongly irradiated NaCl-K crystals: Manifestation of quasi-one-dimensional behavior of electrons.
We have performed electron spin resonance (ESR), nuclear magnetic resonance (NMR) and static magnetic susceptibility measurements on heavily irradiated NaCl-KBF 4 single crystals in the temperature range 4.2 < T < 350 K. In these samples, up to about 10% of the NaCl molecules are transformed into extremely small metallic Na particles and Cl 2 precipitates. At high temperatures a oneline ESR signal, i.e. common mode due to strong exchange interaction between conduction electrons and F-aggregate centres, is observed. We propose that the smooth decrease of the ESR spin susceptibility with decreasing temperature, which can be as large as 50%, is due to a metal-insulator transition, taking place at about 40 K. In the same temperature range, the linewidth increases by 18±2 G with decreasing temperature. This anomalous broadening is explained by a reduction of the exchange narrowing at low temperatures. NMR spinlattice relaxation on 23 Na shows a Korringa-type behaviour down to 10 K, which suggests that the conducting phase in heavily irradiated NaCl-KBF 4 behaves as a three-dimensional metal. SQUID experiments have revealed antiferromagnetic ordering at 40 K and a ferromagnetic phase below 20 K. The nature of the observed effects is discussed.
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ESR, NMR and static magnetic susceptibility measurements of heavily irradiated NaCl-K and NaCl-KBF 4 are reported. Up to 10% of the NaCl-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 160 K 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 metalinsulator 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.
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