Effect of DNA Coating on Magnetic Relaxation in $\gamma$Fe$_{2}$O $_{3}$ Nanoparticles

In this paper, we compare the magnetic relaxation of DNA-coated gammaFe
₂
O
₃
with that of parent 7-nm gammaFe
₂
O
₃
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
=1.3times10
¹⁶
Hz, T
_a
= 2760 K(2960 K), and T
₀
= 40 K(20 K) for the uncoated (DNA-coated) gammaFe
₂
O
₃
. 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
_m
Delta log f) is determined to be 0.04(0.06) for the uncoated (coated) gammaFe
₂
O
₃
. These results show only minimal changes in the magnetic dynamics of gammaFe
₂
O
₃
upon DNA coating.