Effect of DNA Coating on Magnetic Relaxation in γFe2O 3 Nanoparticles

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 T_B (where chi´ peaks) with frequency are analyzed using the relation: T_B=T₀+[T_a/ln(f₀/f)] derived from Vogel-Fulcher relaxation, where T_a(T₀) measures the effective energy barrier (interparticle interaction). The fit to the data yields f₀=1.3times10¹⁶ Hz, T_a= 2760 K(2960 K), and T₀= 40 K(20 K) for the uncoated (DNA-coated) gammaFe₂O₃. From the relative shift DeltaT_m of T_m (the temperature where chi´´ peaks) with change Delta log f in frequency, the parameter Phi=DeltaT_m/(T_mDelta 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.