NMR Spin-Echo Study of the Domain Wall Pinning in Cobalt Micropowders

The pinning force of domain walls was studied by the NMR two-pulse spin-echo method using the action of an additional magnetic video-pulse. It is shown that the pinning force value H-0 is inversely proportional to the duration tau(m) of the magnetic video-pulse. In addition, the area of the magnetic video-pulse A(m) = H-0 tau(m) turned out to be the constant for all threshold durations of the magnetic video-pulse. The dependence of the pinning force H-0 on the external magnetic field He is also studied. It is shown that up to 3 kOe, a linear dependence of H-0 on H-e is observed. This indicates that, as He increases, the domain walls are distributed over positions corresponding to the stronger pinning centers.