Nanocrystalline CoFe2O4 Research Articles

Low temperature magnetic relaxation and quantum tunneling in nanocrystalline particles (abstract)

We report measurements of the magnetic relaxation rate versus temperature for ferrofluid and magnetic-glass samples, which are formed by a modification of nanocomposite material consisting of nanocrystalline CoFe2O4 and polymer. The magnetic properties of the samples have also been studied by using SHE-SQUID at different temperatures (1.8–300 K) with low and high applied magnetic field (−5 T to 5 T). The magnetic relaxation in two samples show a perfect logarithmic dependence on the time, i.e., M(t)=M(t0)[1−S ln(t/t0)], in accordance with the ZFC-FC results which indicate that there is wide energy distribution. The temperature independence of magnetic viscosity S≡[1/M(t0)dM/d]ln t below several Kelvin for the two samples gives clear evidence of macroscopic quantum tunneling of magnetization, in accordance with current theories of quantum tunneling of magnetization.