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

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 CoFe 2 O 4 and polymer. 1 The magnetic properties of the samples have also been studied by using SHE-SQUID at different temperatures ͑1.8 -300 K͒ with low and high applied magnetic field ͑Ϫ5 T to 5 T͒. The magnetic relaxation in two samples show a perfect logarithmic dependence on the time, i.e., M (t)ϭM (t 0 )[1ϪS ln(t/t 0 )], in accordance with the ZFC-FC results which indicate that there is wide energy distribution. The temperature independence of magnetic viscosity Sw[1/M (t 0 )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.