Effect of DNA coating on magnetic relaxation in γFe2O3 nanoparticles

In this paper, we compare the magnetic relaxation of DNA-coated gamma Fe2O3 with that of parent 7-mn gamma Fe2O3 particles by measuring the temperature dependence of AC susceptibilities (chi ' and chi '') at frequency f = 0.1, 1, 10, 100, and 1000 Hz and electron magnetic resonance (EMR) at 9.28 GHz. Changes in the blocking temperature T-B (where chi ' peaks) with frequency are analyzed using the relation: T-B = T-0 + [T-a/ln(f(0)/f)] derived from Vogel-Fulcher relaxation, where T-a (T-0) measures the effective energy barrier (interparticle interaction). The fit to the data yields f(0) = 1.3 x 10(16) Hz, T-a = 2760 K(2960 K), and T-0 = 40 K(20 K) for the uncoated (DNA-coated) gamma Fe2O3. From the relative shift Delta T-m of T-m (the temperature where chi '' peaks) with change Delta log f in frequency, the parameter Phi = Delta T-m/(T-m Delta log f) is determined to be 0.04(0.06) for the uncoated (coated) gamma Fe2O3. These results show only minimal changes in the magnetic dynamics of gamma Fe2O3 upon DNA coating.