Temperature dependence of the spin relaxation time of Fe3O4 and hemozoin superparamagnetic nanocrystals

•We report a novel experimental and theoretical approach to evaluate the electron spin-lattice relaxation rates for superparamagnetic nanocrystals in solutions, applied to Fe3O4 and hemozoin.•We report a novel method to evaluate electric charge fluctuation rates in solutions.•We report a novel method to evaluate micro-viscosity of liquids, based on the known size of the diffusive species.

We report experimental temperature and concentration dependences of the natural spin relaxation time of superparamagnetic Fe3O4 and hemozoin nanocrystals. We recorded the 1H NMR spectrum of 0.5% benzene dissolved in CS2 in function of superparamagnetic particle concentration and temperature, interpreting the 7.261 ± 0.002 ppm benzene line broadening. Our model for the line broadening includes natural, hyperfine magnetic dipole-dipole, and contact hyperfine contributions. The latter arises due to exchange interaction between benzene molecules and suspended nanoparticles. Estimated frequency of fluctuation in the 1 cm3 sample volume is in the 107 Hz scale. Estimated natural electron spin-lattice relaxation frequencies of the superparamagnetic nanocrystals using frequency of fluctuations, and developed theoretical model applied to analysis of experimental data are in good agreement between each other. Thus the presently developed approach may be used to study fluctuations and natural spin-lattice relaxation frequencies in different media.

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