Abstract
Macroscopic resonant quantum tunneling of magnetization has been observed in antiferromagnetic ferritin particles. The dependence of magnetic viscosity on the applied magnetic field has been systematically investigated in the temperature range 1.8-10 K. The zero maximum in field dependence of viscosity and the maximum in the field dependent blocking temperature are interpreted to be due to the resonant spin tunneling between matching spin levels. (C) 1998 American Institute of Physics. [S0021-8979(98)53311-7].