Skip to Main Content
In this paper, we compare the magnetic relaxation of DNA-coated gammaFe2O3 with that of parent 7-nm gammaFe2O3 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 TB (where chi' peaks) with frequency are analyzed using the relation: TB=T0+[Ta/ln(f0/f)] derived from Vogel-Fulcher relaxation, where Ta(T0) measures the effective energy barrier (interparticle interaction). The fit to the data yields f0=1.3times1016 Hz, Ta= 2760 K(2960 K), and T0= 40 K(20 K) for the uncoated (DNA-coated) gammaFe2O3. From the relative shift DeltaTm of Tm (the temperature where chi'' peaks) with change Delta log f in frequency, the parameter Phi=DeltaTm/(TmDelta log f) is determined to be 0.04(0.06) for the uncoated (coated) gammaFe2O3. These results show only minimal changes in the magnetic dynamics of gammaFe2O3 upon DNA coating.