Skyrmions in Antiferromagnets

Calculations of skyrmions in antiferromagnets (AFMs) are presented, and their properties compared with skyrmions in corresponding ferromagnets (FMs). The rates of skyrmion collapse and escape through the boundary of a track, as well as the binding to and collapse at a non-magnetic impurity is calculated as a function of applied magnetic field. In the absence of an applied magnetic field, the activation energy for skyrmion annihilation is the same. The pre-exponential factor in the Arrhenius rate law is, however, different because skyrmion dynamics is different in the two systems. An applied magnetic field has opposite effects on skyrmions in the two types of materials. In AFM the rate of collapse of skyrmions as well as the rate of escape through the edge of a magnetic strip decreases slightly with increasing field, while these rates increase strongly for a skyrmion in the corresponding FM when the field is directed antiparallel to the magnetization in the center of the skyrmion. A non-magnetic impurity is less likely to trap a skyrmion in AFM especially in the presence of a magnetic field. This, together with the established fact that a spin polarized current moves a skyrmion in an AFM in the direction of the current, while in a FM the skyrmion moves at an angle to the current, demonstrates that skyrmions in AFM have several advantageous properties over skyrmions in FM for memory and spintronic devices.