Probing spin-spin and spin-lattice relaxation through electron paramagnetic resonance study of nanoscale WO_3-x system

We show that nanoscale tungsten oxides, which are rich in oxygen deficiencies, could exhibit enhanced spin-spin relaxation over spin-lattice relaxation at low temperature. The morphological features were viewed through high resolution transmission electron microscopy. Whereas, participation of electron spin states originated from paramagnetic centers was revealed through electron paramagnetic resonance (EPR) spectra at low (~150 K) and high temperature (~298 K). Compared to bigger sized WO₃ particles (prepared at pH = 2), the smaller ones (prepared at pH = 5.5) were supposed to hold relatively large spin concentration owing to proportionately higher concentration of paramagnetic centers/ionized oxygen vacancies. For a given nanosystem, the dominance of spin-spin interaction over spin-lattice interaction was also ascertained at low temperature.