Superparamagnetic behaviour and T 1 , T 2 relaxivity of ZnFe 2 O 4 nanoparticles for magnetic resonance imaging.

In the present study, ZnFe2O4nanoparticles were synthesized by the chemical co-precipitation followed by calcinations at 473 and 673 K for 4 h. Particle sizes obtained were 4 and 6 nm for the calcination temperatures of 473 and 673 K, respectively. To study the origin of system’s low temperature spin dynamic behaviour, temperature dependence of susceptibilitywas investigated as a function of particle size and frequency. Slight increase in the grain size from 4 nm at 473 K to 6 nm at 673 K has led to a peak shift of temperature dependence of susceptibility measured at a constant frequency of 400 Hz. Temperature dependence ofat different frequencies also resulted in peak shift. Relaxation time dependence of peak temperature obeys a power law, which provides the fitting parameters within the range of superparamagnetic nature of the particles. Further, dependence of relaxation time and peak temperature obeys Vogel–Fulcher law rather than Néel–Brown equation demonstrating that the particles follow the behaviour of superparamagnetism of slightly interacting system. Spin–lattice,T1and spin–spin,T2relaxivity of proton of the water molecule in the presence of chitosan-coated superparamagnetic ZnFe2O4nanoparticle yields the values of 0.002 and 0.360 s−1 per ppm. [ABSTRACT FROM AUTHOR]