MAGNETIC-PROPERTIES AND DOMAIN-WALL MOTION IN SINGLE-CRYSTAL BAFE10.2SN0.74CO0.66O19

The magnetic properties of BaFe12O19 and BaFe10.2Sn0.74Co0.66O19 singl e crystals have been investigated in the temperature range (1.8 to 320 K) with a varying field from -5 to +5 T applied parallel and perpendi cular to the c axis. Low-temperature magnetic relaxation, which is asc ribed to the domain-wall motion, was performed between 1.8 and 15 K. T he relaxation of magnetization exhibits a linear dependence on logarit hmic time. The magnetic viscosity extracted from the relaxation data, decreases linearly as temperature goes down, which may correspond to t he thermal depinning of domain walls. Below 2.5 K, the viscosity begin s to deviate from the linear dependence on temperature, tending to be temperature independent. The near temperature independence of viscosit y suggests the existence of quantum tunneling of antiferromagnetic dom ain wall in this temperature range.